INFECTION CONTROL & PREVENTION

Is there airborne spread of SARS-CoV-2? How is air ventilation relevant for the spread of SARS-CoV-2?

Answered in May 10, 2020 Newsletter

  • The primary mechanisms of SARS-CoV-2 transmission are through respiratory droplets and close contact.(1) Although some studies have detected SARS-CoV-2 RNA in air samples from hospitals with COVID-19 patients,(2,3,4) cell culture of SARS-CoV-2 (i.e.: ability to grow the virus) from those RNA-positive air samples has not been successful.(2) Collectively, current evidence does not support airborne transmission of SARS-CoV-2.

  • While patients with diseases which are airborne, such as measles and tuberculosis, are ideally placed in airborne-infection isolation rooms (AIIRs), this precaution is not necessary for diseases spread by droplets and thus not needed for cases of COVID-19.(5) The CDC recommends that ventilation systems be properly maintained and installed, and that COVID-19 suspected or positive patients requiring hospitalization be placed in single rooms with the door closed.

  • Shared Health Guidelines state that AIIRs are not required for all aerosol-generating medical procedures (AGMPs), although they are preferred for high risk procedures. In hospitalized patients with COVID-19, the risk of spreading infection during patient transfer to an AIIR must be weighed against the potential benefit.

  1. Interim Infection Prevention and Control Recommendations for Patients with Suspected or Confirmed Coronavirus Disease 2019 (COVID-19) in Healthcare Settings. Centers for Disease Control and Prevention. 2020 [cited 2020 May 6].

  2. Santarpia JL, Rivera DN, Herrera V, Morwitzer MJ, Creager H, Santarpia GW, et al. Transmission Potential of SARS-CoV-2 in Viral Shedding Observed at the University of Nebraska Medical Center. medRxiv [Preprint]. 2020 Jan.  

  3. Liu Y, Ning Z, Chen Y, Guo M, Liu Y, Gali NK, et al. Aerodynamic analysis of SARS-CoV-2 in two Wuhan hospitals. Nature. 2020. 

  4. Guo Z-D, Wang Z-Y, Zhang S-F, Li X, Li L, Li C, et al. Aerosol and surface distribution of severe acute respiratory syndrome coronavirus 2 in hospital wards, Wuhan, China, 2020. Emerg Infect Dis. 2020.  

  5. Transmission-Based Precautions. Centers for Disease Control and Prevention. 2016 [cited 2020 May 6].

Is Non-Invasive Ventilation (NIV – i.e.: CPAP and BiPAP) a risk for aerosolization of SARS-CoV-2 particles? How can this risk be mitigated?

Answered in May 10, 2020 Newsletter

  • To date, no study has assessed aerosolization of SARS-CoV-2 by NIV. NIV is associated with the production of large droplets >10µm which, due to their size, mostly fall to surfaces within a one-meter radius.(1) Exposure to air exhaled during NIV is greatest within a 1m radius of a patient.(2) Multiple factors affect the degree of air dispersion with NIV such as mask type, mask seal, pressure settings, and the application of filters to inspiratory and expiratory ports. NIV via helmets with tight air cushions results in negligible dispersion of exhaled air from patients.(3)

  • No study has shown that NIV causes dispersion of pathogens in the environment. Additionally, NIV has not been consistently found to be associated with increased risk for secondary infections in healthcare workers (HCW). However, a meta-analysis that included two studies from Toronto, identified caring for SARS patients on NIV was a risk factor for HCW infection.(4)

  • Local and international infection prevention and control guidelines treat NIV as an aerosol generating procedure. Thus, in patients with COVID-19 on NIV, a N95 respirator should be worn when providing care. Measures to reduce air dispersion from NIV should be considered. Ideally, NIV should be administered via a full-face, non-vented mask with an expiratory viral filter and good mask seal to minimise droplet dispersion. As another option, CPAP helmets have less air dispersion than standard CPAP masks.(5)

  • At home, both confirmed and suspected COVID-19 patients using NIV should be isolated in a separate room from other members of the household.(6)

 

 

 

  1. Simonds A, Hanak A, Chatwin M, Morrell M, Hall A. Evaluation of droplet dispersion during non-invasive ventilation, oxygen therapy, nebuliser treatment and chest physiotherapy in clinical practice: implications for management of pandemic influenza and other airborne infections. Health Technol Assess 2010;14(46 Article 2).  

  2. Hui DS, Chow BK, Ng SS, et al. Exhaled air dispersion distances during noninvasive ventilation via different Respironics face masks. Chest. 2009;136(4):998‐1005.  

  3. Hui DS, Chow BK, Lo T, et al. Exhaled air dispersion during noninvasive ventilation via helmets and a total facemask. Chest. 2015;147(5):1336‐1343.  

  4. Tran K, Cimon K, Severn M, Pessoa-Silva CL, Conly J. Aerosol generating procedures and risk of transmission of acute respiratory infections to healthcare workers: a systematic review. PloS one. 2012;7(4).  

  5. NHS. Guidance for the role and use of non-invasive respiratory support in adult patients with COVID- 19 (confirmed or suspected) [Internet]. 2020 [updated 2020 Apr 6; cited 2020 May 6].

  6. AHS. Care of the Adult Critically Ill COVID-19 Patient Annex D [Internet]. 2020 [updated 2020 Apr 15; cited 2020 May 6].

Which non-health care related workplaces are at risk for SARS-CoV-2 transmission and why?

Answered in May 10, 2020 Newsletter

  • The risk of SARS-CoV-2 transmission in the workplace is related to the current level of community spread. Workplaces that frequently come into contact with the public and/or have large numbers of employees are at higher risk. Early reported COVID-19 cases linked to occupational exposure in Singapore included employees in the retail and hospitality industry, construction workers and transport workers such as taxi and private hire drivers.(1)

  • To date, there have been seven SARS-CoV-2 outbreaks in meat processing plants across Canada. The outbreak at the Cargill meat packing plant in Alberta is the largest single-site outbreak in Canada, with 921 confirmed cases as of May 1, 2020.(2)

  • The Cargill COVID-19 outbreak highlights many of the challenges for workplace safety during the pandemic. Factors which are thought to have contributed to the outbreak include:(2)

    • Close workplace quarters and high worker density.

    • Delayed initiation of social distancing, physical barriers, and personal protective equipment (PPE).

    • A vulnerable employee population consisting of many temporary foreign workers and recent immigrants. A large proportion of these employees carpool to work or live in multi-family households. 

    • Language barriers may have impacted communication of rapidly changing policies.

  

  1. Koh D. Occupational risks for COVID-19 infection. Occupational Medicine (Oxford, England). 2020 Mar;70(1):3.  

  2. Baum, K. B., Tait C., Grant T. How Cargill became the site of Canada’s largest single outbreak of COVID-19. The Globe and Mail [Internet]. 2020 May 2 [cited 2020 May 6].

What infection prevention and control measure can be instituted at non-health care workplaces to reduce transmission of SARS-CoV-2?

Answered in May 10, 2020 Newsletter

  • One key principle in occupational health is the hierarchy of controls.(1) The first priority is eliminating potential exposure to a hazard, followed by engineering controls (such as workplace structural design), administrative controls (such as workplace procedures), and lastly the use of PPE. The latter methods are less effective as they rely on many individuals’ education and adherence.

  • To avoid spreading SARS-CoV-2, it is recommended to work from home and to self-isolate if symptomatic. If working from home is not possible, other preventative measures should be implemented including the use of physical barriers, physical distancing measures, surface decontamination, and hand hygiene. In settings where physical distancing is challenging, the use of non-medical masks may be used. Studies have shown that cleaning high touch surfaces(2) and regular hand washing(3) reduce the risk of spreading infections within the workplace.

  • Unique measures now instituted at Cargill meat packing plan in Alberta include buses for transportation to the plant, access to translation services, and opening of an isolation centre to accommodate infected employees and close contacts.(4)

  1. Su CP, de Perio MA, Cummings KJ, McCague AB, Luckhaupt SE, Sweeney MH. Case investigations of infectious diseases occurring in workplaces, United States, 2006–2015. Emerging infectious diseases. 2019 Mar;25(3):397. 

  2. Zhang N, Li Y. Transmission of influenza A in a student office based on realistic person-to-person contact and surface touch behaviour. International journal of environmental research and public health. 2018 Aug;15(8):1699. 

  3. Stedman-Smith M, DuBois CL, Grey SF, Kingsbury DM, Shakya S, Scofield J, Slenkovich K. Outcomes of a pilot hand hygiene randomized cluster trial to reduce communicable infections among US office-based employees. Journal of occupational and environmental medicine. 2015 Apr;57(4):374. 

  4. Baum, K. B., Tait C., Grant T. How Cargill became the site of Canada’s largest single outbreak of COVID-19. The Globe and Mail [Internet]. 2020 May 2 [cited 2020 May 6].

Update on screening for SARS-CoV-2 in asymptomatic patients prior to surgeries. (Previously discussed on April 10, 2020.)

Answered in May 10, 2020 Newsletter

  • In a study in New York, 210 asymptomatic pregnant women were screened with RT-PCR for SARS-CoV-2 and 29 (13.7%) were positive, of which only 10% developed symptoms.(1) As discussed March 27th, PCR positivity does not equate to infectivity, so the value of screening is still not clear from this data. 

  • Manitoba guidelines continue to recommend, with the exception of emergency surgeries, that all patients are to isolate for 14 days prior to surgery. If the patient develops symptoms within this period, they are screened for COVID-19 via RT-PCR. If symptoms do not develop, the patient is asked the COVID-19 screening questions and cleared for surgery if screening questions are negative. 

  1. Sutton, Desmond, et al. "Universal screening for SARS-CoV-2 in women admitted for delivery." New England Journal of Medicine (2020).

What is the risk of SARS-CoV-2 transmission for dental healthcare personnel? What are the recommended infection prevention and control measures in dentistry?

Answered in May 1, 2020 Newsletter

Why is there risk?

  • Dental healthcare personnel (DHCP) are at high risk for acquiring and transmitting diseases such as COVID-19 due to their close contact with the nose and oral cavity of patients.

  • Many tools used in dental procedures generate bioaerosols. More specifically, ultrasonic scaler tips and high-speed handpieces with a burr cause the greatest emission of aerosols and splatter during dental procedures.(1)

  • The oral cavity, in particular, may put DHCP at high risk for infection with SARS-CoV-2, as the oral mucosa and tongue express ACE2 (the main receptor for SARS-CoV-2 entry).(2) In patients with COVID-19, saliva has relatively high levels of viral RNA, is a source of live virus particles and may facilitate transmission.(3,4)

 

What do we know about transmission?

  • There is no clinical data quantifying the risk of SARS-CoV-2 transmission during dental practice. However, early in the pandemic, a dental school in Wuhan reported 9 cases of COVID-19 among staff.(5) In response, they introduced stringent infection control measures and since then, no DHCP have been infected despite 169 staff members treating >700 patients for dental emergencies.

  • In the United States, no DHCP have been infected to date.(6)

 

What are Manitoba Guidelines for dental practice in the COVID-19 pandemic?

  • The Manitoba Dental Association (MDA) has released infection prevention and control (IP&C) guidelines for COVID-19 in dental settings. See guidelines released on April 30, 2020 for the full list of recommendations or their website for the latest updates. Key points are:

    • Strong recommendation that only emergent and urgent dental procedures should proceed with appropriate IP&C measures. Aerosol generating procedures should be reduced where possible.

    • Triage by phone: only asymptomatic patients with urgent or emergent dental conditions seen in person.

    • Patients with suspected or confirmed COVID-19: dental treatment should be provided in a hospital/facility with airborne precautions, not a regular dental operatory.

    • Reduce cross-contamination: strict hand hygiene, disinfect all surfaces and equipment and consider alternating operatory use to allow for time for proper air exchange between patients.

 

  • The Government of Manitoba has announced that dental offices are allowed to reopen as of May 4, 2020, with measures to ensure patient safety. Some added restrictions include the use of the self-screening tool prior to patients booking an appointment and maintaining physical distancing while in waiting rooms.  

  1. Szymańska J. Dental bioaerosol as an occupational hazard in a dentist’s workplace. Ann Agric Environ Med [Internet]. 2007;14, 203-207.

  2. Xu H, Zhong L, Deng J, Peng J, Dan H, Zeng X, et al. High expression of ACE2 receptor of 2019-nCoV on the epithelial cells of oral mucosa. Int J Oral Sci [Internet]. 2020;12(8).  

  3. Wyllie AL, Fournier J, Casanovas-Massana A, Campbell M, Tokuyama M, Vijayakumar P, Geng B, Muenker MC, Moore AJ, Vogels CB, Petrone ME. Saliva is more sensitive for SARS-CoV-2 detection in COVID-19 patients than nasopharyngeal swabs. medRxiv [preprint]. 2020 Jan 1.  

  4. To KK, Tsang OT, Yip CC, Chan KH, Wu TC, Chan JM, Leung WS, Chik TS, Choi CY, Kandamby DH, Lung DC. Consistent detection of 2019 novel coronavirus in saliva. Clinical Infectious Diseases. 2020 Feb 12.  

  5. Meng L, Hua F, Bian Z. Coronavirus Disease 2019 (COVID-19): Emerging and Future Challenges for Dental and Oral Medicine. J Dent Res [Internet]. 2020/03/12. 2020 May;99(5):481–7.  

  6. Interim Infection Prevention and Control Guidance for Dental Settings During the COVID-19 Response [Internet]. Centers for Disease Control and Prevention. 2020 [cited 2020 Apr 29].

Can SARS-CoV-2 be transmitted via food or food packing?

Answered in May 1, 2020 Newsletter

  • There is no evidence of SARS-CoV-2 transmission via food or food packaging to date.(1) Similarly, there were no SARS or MERS cases associated with food in previous outbreaks.(2)

  • While coronaviruses cannot replicate in food, food can act as a fomite, like any other surface, and it is important to practice proper hand hygiene in the preparation and handling of all food products. 

  1. CDC. Coronavirus Disease 2019 Frequently Asked Questions [Internet]. 2020 [cited 2020 Apr 28]. 

  2. Galanakis C. The Food Systems in the Era of the Coronavirus (COVID-19) Pandemic Crisis. Foods. 2020;9(4):523.

What updates are there about the surface stability of SARS-CoV-2? 

Answered in May 1, 2020 Newsletter

  • As we discussed on March 20, 2020, following the dispersion of concentrated aerosols of SARS-CoV-2, viable virus was recovered from plastics and stainless steel for up to 72 hours, and from cardboard and copper for up to 24 hours.(1) However, these experiments were conducted under ideal lab conditions, using a selected particle size and viral inoculum.(2) As such, they may not be reflective of real life conditions.

  • Other coronaviruses (e.g. SARS-CoV and MERS-CoV) persist on plastic in experimental conditions for 8 hours up to 9 days, depending on the viral strain and titer studied.(3) Furthermore, the capsid protein structure of SARS-CoV-2 may help it persist longer in bodily fluids and in the environment.(4)

  • Studies in natural environments like hospital wards have found SARS-CoV-2 RNA on numerous surfaces.(5,6) However, they have not reported on the presence or absence of live virus in these settings, nor the exact role of these fomites in transmission of the virus.

  • Fortunately, routine hospital cleaning with ethanol-based products effectively reduces surface contamination by SARS-CoV-2 and other coronaviruses.(3,6)

  1. Van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med. 2020 

  2. Schwartz KL, Kim J, Garber G. Stability and Viability of SARS-CoV-2. N Engl J Med. 2020;382.  

  3. Kampf G, Todt D, Pfaender S, Steinmann E. Persistence of coronaviruses on inanimate surfaces and their inactivation with biocidal agents. J Hosp Infect. 2020;104(3):246–51. 

  4. Goh GK, Dunker AK, Foster JA, Uversky VN. Shell disorder analysis predicts greater resilience of the SARS-CoV-2 (COVID-19) outside the body and in body fluids. Microbial Pathogenesis. 2020 Mar 31:104177.  

  5. Guo Z-D, Wang Z-Y, Zhang S-F, Li X, Li L, Li C, et al. Aerosol and surface distribution of severe acute respiratory syndrome coronavirus 2 in hospital wards, Wuhan, China. Emerg Infect Dis. 2020;26(7).  

  6. Ong SWX, Tan YK, Chia PY, Lee TH, Ng OT, Wong MSY, et al. Air, Surface Environmental, and Personal Protective Equipment Contamination by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) From a Symptomatic Patient. JAMA. 2020;323(16):1610–2.

Is there evidence for fecal-oral transmission of SARS-CoV-2?

Answered in May 1, 2020 Newsletter

  • Fecal-oral transmission has not been documented for SARS-CoV-2. However, gastrointestinal symptoms have been observed in some COVID-19 cases.(1) Fecal shedding of SARS-CoV-2 has been detected by RT-PCR (56% in one prospective study)(2) even in patients presenting with only respiratory symptoms.(2,3) Successful culturing of live virus from fecal samples has also been reported.(3)

  • The overall significance of fecal-oral transmission in the COVID-19 pandemic is still under investigation. Regardless, hand hygiene and surface decontamination protect against both fecal-oral and droplet routes of transmission.

  1. Guan WJ, Ni ZY, Hu Y, Liang WH, Ou CQ, He JX, Liu L, Shan H, Lei CL, Hui DS, Du B. Clinical characteristics of coronavirus disease 2019 in China. New England Journal of Medicine. 2020 Feb 28.  

  2. Wu Y, Guo C, Tang L, Hong Z, Zhou J, Dong X, Yin H, Xiao Q, Tang Y, Qu X, Kuang L. Prolonged presence of SARS-CoV-2 viral RNA in faecal samples. Lancet Gastroenterol Hepatol. 2020 May 1;5(5):434-5.  

  3. Amirian ES. Potential Fecal Transmission of SARS-CoV-2: Current Evidence and Implications for Public Health. International Journal of Infectious Diseases [preproof]. 2020 Apr 23.

When are people with SARS-CoV-2 infection no longer contagious? How has this been determined in viral respiratory illnesses prior to COVID-19?

Answered in April 24, 2020 Newsletter

  • Thus far, we do not have robust data to reliably determine when a patient infected with SARS-CoV-2 is no longer contagious. Studies of viral shedding and transmission in SARS-CoV-2 and other respiratory illnesses have provided some information, but many limitations remain.

  • Viral shedding can be measured by PCR or culture. PCR measures the presence of viral genetic material, but does not indicate whether this material is “viable” or infectious.(1) Viral culture can determine if a virus can replicate within cells, and the superiority of culture for determining the presence of infectious virus has been demonstrated in animal models of influenza.(2) However, it is a more complex and less sensitive method than PCR-based testing and results of either method do not necessarily correlate with whether a person can transmit virus or not. 

  • For some illnesses, such as influenza A, levels of viral shedding measured by PCR decrease predictably in relation to the resolution of clinical illness.(3) However, in a study investigating transmission among household contacts, the infectious period of the virus did not correlate well with viral shedding measured by PCR.(4)  Furthermore, even closely related influenza A and B have different periods of viral shedding relative to symptoms, so it is difficult to make generalizations among different viral respiratory illnesses. Additionally, patient age and immune status have an effect on duration of viral shedding.(5)

  1. De Serres G, Rouleau I, Hamelin ME, Quach C, Skowronski D, Flamand L, et al. Contagious period for pandemic (H1N1) 2009. Emerg Infect Dis [Internet]. 2010 May;16(5):783–8. 

  2. Inagaki K, Song MS, Crumpton JC, DeBeauchamp J, Jeevan T, Tuomanen EI, Webby RJ, Hakim H. Correlation between the interval of influenza virus infectivity and results of diagnostic assays in a ferret model. The Journal of infectious diseases. 2016 Feb 1;213(3):407-10. 

  3. Ip DKM, Lau LLH, Chan KH, Fang VJ, Leung GM, Peiris MJS, et al. The Dynamic Relationship between Clinical Symptomatology and Viral Shedding in Naturally Acquired Seasonal and Pandemic Influenza Virus Infections. Clin Infect Dis [Internet]. 2016;62(4):431–7. 

  4. Tsang TK, Fang VJ, Chan K-H, Ip DKM, Leung GM, Peiris JSM, et al. Individual Correlates of Infectivity of Influenza A Virus Infections in Households. PLoS One [Internet]. 2016 May 6;11(5):e0154418. 

  5. Piralla A, Zecca M, Comoli P, Girello A, Maccario R, Baldanti F. Persistent rhinovirus infection in pediatric hematopoietic stem cell transplant recipients with impaired cellular immunity. Journal of Clinical Virology. 2015 Jun 1;67:38-42.

What can epidemiologic data tell us about the infective period of COVID-19?

Answered in April 24, 2020 Newsletter

  • The viral shedding and transmission patterns of SARS-CoV-2 appear more similar to those of influenza, compared to SARS-CoV or MERS. With SARS-CoV-2 infection, viral load and contagiousness seem to peak around symptom onset.(1,2)

  • A retrospective study of transmission pairs of COVID-19 estimated that the infectious period starts 2.3 days prior to symptom onset, peaks around the time of symptom onset, and declines within 7 days.(2) One caveat is that the measured period of infectivity in this study may have been influenced by hospitalization and self-isolation procedures.

  1. Cowling BJ, Leung GM. Epidemiological research priorities for public health control of the ongoing global novel coronavirus (2019-nCoV) outbreak. Euro Surveill [Internet]. 2020/02/11. 2020 Feb;25(6):2000110.

  2. He X, Lau EH, Wu P, Deng X, Wang J, Hao X, Lau YC, Wong JY, Guan Y, Tan X, Mo X. Temporal dynamics in viral shedding and transmissibility of COVID-19. Nature Medicine. 2020 Apr 15:1-4.

What do we know about the infective period of SARS-CoV-2 infection from studies of viral shedding?

Answered in April 24, 2020 Newsletter

  • Based on multiple studies, SARS-CoV-2 detection by PCR tends to peak around the time of symptom onset but can stay positive at a low level for extended periods. One study showed viral shedding in hospitalized patients measured by PCR lasting a median of 20 days, with a maximum of 37 days in one patient.(1) Similarly, PCR detection persisted for up to 28 days post symptom onset in a small prospective case series of German patients with mild COVID-19 disease.(2) However, virus isolation by culture was successful only up to 8 days post symptom onset, and only in those with higher RNA copy levels measured by PCR.

  • To date, there has not been a study of live viral isolation in severe COVID-19 cases. However, it has been observed that severe cases of COVID-19 have higher viral loads and a longer period of viral shedding measured by PCR compared to mild or moderate cases.(3,4)

  1. Zhou, F. et al. Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study. The Lancet. 2020 March 9. 

  2. Wölfel R, Corman VM, Guggemos W, Seilmaier M, Zange S, Müller MA, Niemeyer D, Jones TC, Vollmar P, Rothe C, Hoelscher M. Virological assessment of hospitalized patients with COVID-2019. Nature. 2020 Apr 1:1-0. 

  3. Liu Y, Yan LM, Wan L, Xiang TX, Le A, Liu JM, Peiris M, Poon LL, Zhang W. Viral dynamics in mild and severe cases of COVID-19. The Lancet Infectious Diseases. 2020 Mar 19. 

  4. Xu K, Chen Y, Yuan J, Yi P, Ding C, Wu W, Li Y, Ni Q, Zou R, Li X, Xu M. Factors associated with prolonged viral RNA shedding in patients with COVID-19. Clinical Infectious Diseases. 2020 Apr 9.

How are different jurisdictions approaching the issue of discontinuing precautions and allowing for return to work after SARS-CoV-2 infection?

Answered in April 24, 2020 Newsletter

  • The decision to discontinue self-isolation and precautions for positive cases who have experienced symptom resolution has been made in different jurisdictions by either a test-based strategy (two negative specimens by PCR collected ≥24 hours apart) or a non-test-based strategy (based on the number of days since symptom onset and resolution).(1,2)

  • Several centers have adopted more complex hybrid approaches, accounting for potential differences in risk of transmission on account of immune compromise, age, or occupation.(3)

  • Without a clear understanding of infectivity, there is no universal strategy for discontinuing precautions or instituting back-to-work policies. Decisions need to incorporate local testing capacity, workforce demands, unique patient circumstances, and evolving evidence. Further, specific cases may demand a more cautious approach, including healthcare workers, immunocompromised patients, and patients who are being transferred to high-risk settings such as long-term care homes.

  • Even after isolation precautions are discontinued, affected individuals should continue to adhere to practices such as physical distancing, hand hygiene, and wearing a face mask when appropriate.

  • Current Guidelines in Manitoba: For hospitalized patients, isolation precautions are discontinued in consultation with the Infection Prevention and Control service.

  1. Centers for Disease Control and Prevention. Coronavirus Disease 2019 Ending Home Isolation [Internet]. 2020 [cited 2020 Apr 22].

  2. Centers for Disease Control and Prevention. Coronavirus Disease 2019 Discharging Hospitalized Patients [Internet]. 2020 [cited 2020 Apr 22].

  3. European Centre for Disease Control and Prevention. Guidance for discharge and ending isolation in the context of widespread community transmission of COVID-19-first update Scope of this document. 2020 [cited 2020 Apr 22].

What personal protective equipment (PPE) is appropriate for home healthcare workers in the setting of COVID-19?

Answered in April 24, 2020 Newsletter

  • Patients requiring care at home may be predisposed to infectious disease acquisition and adverse outcomes due to factors such as age and comorbidities.(1) Home healthcare workers (HCWs) have been implicated in the spread of infections such as MRSA to their patients.(2) Conversely, home HCWs face unique challenges, such as a lack of control over the care environment, which can limit infection prevention by environmental/engineering strategies. This places greater importance on individual use of PPE.(3,4) 

  • Unfortunately, no data has been published on this issue in COVID-19. However, because of the potential for asymptomatic spread of COVID-19, all home visits should be considered a potential risk to both the patient and HCW.

  • Shared Health Guidelines in Manitoba state that a medical mask and eye protection should be used by HCWs for all home visits. Gloves and gowns are only required for confirmed or suspected COVID-19 clients and where they are required per routine practice.

  1. Smith PW, Hewlett, AL. Epidemiology and Prevention of Infections in Home Healthcare. In: Mayhall CG. Hospital epidemiology and infection control. 4th edition. Philadelphia, PA. Lippincott Williams & Wilkins; 2012 Feb 20.

  2. Lescure F-X, Locher G, Eveillard M, Biendo M, Agt SV, Loup GL, et al. Community-Acquired Infection With Healthcare-Associated Methicillin-Resistant Staphylococcus aureus: The Role of Home Nursing Care. Infection Control & Hospital Epidemiology. Cambridge University Press; 2006;27(11):1213–8.

  3. Ward D. Implementing infection prevention and control precautions in the community. Br J Community Nurs. 2017;22(3):116–8.

  4. Elmashae RBY, Grinshpun SA, Reponen T, Yermakov M, Riddle R. Performance of two respiratory protective devices used by home-attending health care workers (a pilot study). J Occup Environ Hyg. 2017;14(9):D145–9.

What is the efficacy of eye protection in preventing transmission of SARS-CoV-2?

Answered in April 17, 2020 Newsletter

  • Some patients with COVID-19 have developed conjunctivitis, although their route of acquisition is unknown.(1)

  • The eyes can be a portal of entry for respiratory viruses. A study of intubations during the 2003 SARS outbreak found that inadequate eye protection was a significant risk factor for healthcare worker acquired infection.(2) In a laboratory setting, it has been shown that eye protection can prevent transocular acquisition of aerosolized viruses.(3) Outside of aerosol generating procedures, the benefit of eye protection has not been established as clearly, but it is a reasonable precaution.

  • Bottom Line: Eye protection is recommended (i.e. goggles, face shield, or mask with visor) in combination with other appropriate PPE when providing routine care to patients with COVID-19 patients and is critically important during aerosol generating procedures (see Manitoba PPE guidelines).

  1. Wu P, Duan F, Luo C, Liu Q, Qu X, Liang L, Wu K. Characteristics of ocular findings of patients with coronavirus disease 2019 (COVID-19) in Hubei province, China. JAMA ophthalmology. 2020 Mar 31. 

  2. Raboud J, Shigayeva A, McGeer A, Bontovics E, Chapman M, Gravel D, Henry B, Lapinsky S, Loeb M, McDonald LC, Ofner M. Risk factors for SARS transmission from patients requiring intubation: a multicentre investigation in Toronto, Canada. PLoS One. 2010;5(5). 

  3. Bischoff WE, Reid T, Russell GB, Peters TR. Transocular entry of seasonal influenza–attenuated virus aerosols and the efficacy of N95 respirators, surgical masks, and eye protection in humans. Journal of Infectious Diseases. 2011 Jul 15;204(2):193-9.

Does N95 fit testing matter?

Answered in April 17, 2020 Newsletter

  • Yes! The protection provided by N95 respirators is increased when proper fit testing is instituted.(1) Studies of different N95 mask types in different populations report wide variations in the percentage of tested people with effective protection (the pass rate). Mask are certified based on their filtering, but not based on fit, and when several models are trialled the pass rate for any model is often under 50%.2,3 However, when workplaces choose a model based on experience in their population, the pass rates are generally very high (>85%), and only a limited number of alternative options are needed.(2) Thus, the likelihood of protection from using a hospital’s chosen model is likely much higher than an off-the-shelf alternative.

  • Unfortunately, user-seal checks have low accuracy in predicting protection.(3)

  • A substantial benefit of mask fit testing programs is that training and practice in proper donning of N95 respirators leads to significantly more people being protected by a particular mask type.(4) See video on donning training for 3M: 1870 mask, one of the N95 respirators available in Manitoba facilities.

  • Bottom line: Shared Health recommends only using the respirator make, model, and size for which fit testing has been completed.

  1. Centers for Disease Control and Prevention. Laboratory performance evaluation of N95 filtering facepiece respirators, 1996. MMWR Morb Mortal Wkly Rep. 1998 Dec;47(48):1045–9.

  2. Shaffer, Ronald E., and Larry L. Janssen. Selecting models for a respiratory protection program: what can we learn from the scientific literature?. American journal of infection control. 43.2 (2015): 127-132.

  3. Lam SC, Lee JKL, Yau SY, Charm CYC. Sensitivity and specificity of the user-seal-check in determining the fit of N95 respirators. J Hosp Infect. 2011 Mar;77(3):252–6.

  4. Lee MC, Takaya S, Long R, Jofee AM. Respirator-fit testing: does it ensure the protection of healthcare workers against respirable particles carrying pathogens? Infection Control and Hospital Epidemiology. 2008. Dec; 29 (12). 1149-56.

Update on evidence related to masks. Originally answered in March 27 Newsletter

 

Answered in April 17, 2020 Newsletter

Which mask/respirator is better for COVID-19 patient care?

  • To date, there is no evidence to suggest that surgical masks are inferior to N95 respirators in protecting healthcare workers from infection during non-aerosolizing patient interactions.(1) This supports the current guideline that N95 respirators should be worn during aerosol-generating medical procedures and surgical masks for all other patient care.

 

Are there any updates on the decontamination of N95 respirators?

  • This is an active area of ongoing research. One method, the Battelle Decontamination System, has been authorized in the USA as an emergency measure to decontaminate N95 respirators via vapour phase hydrogen peroxide (VPHP).(1) The 480 minute decontamination process maintains adequate fit and filtration of the tested N95 brand for up to 20 cycles.(2) Research at the University of Manitoba has similarly shown that the structural and functional integrity of N95s is maintained for up to 10 cycles of decontamination with VPHP or autoclaving.(3)

  • No effective methods of N95 decontamination that can be employed at home have been published. 

 

Are there any updates on the efficacy of cloth masks?

  • Cloth masks are now recommended in public to prevent the spread of virus from asymptomatic carriers. No clinical data is available on the effectiveness of this approach, but evidence from experimental settings suggest it may reduce viral transmission, if used together with hand hygiene and physical distancing.(1)

  • The filtering efficiency of cloth masks depends on fabric composition, particles to which the mask is exposed, and seal.(2) Washing and drying have been shown to decrease filtering efficiency(3) and thus, cloth masks should be replaced after multiple uses.

  • The CDC has provided tutorials on making homemade masks using cotton fabric.

Which mask/respirator is better for COVID-19 patient care?

  1. Bartoszko JJ, Farooqi MAM, Alhazzani W, et al. Medical Masks vs N95 Respirators for Preventing COVID-19 in Health Care Workers A Systematic Review and Meta-Analysis of Randomized Trials. Influenza and Other Respiratory Viruses. 2020 Apr 4

 

Are there any updates on the decontamination of N95 respirators?

  1. CDC. COVID-19 Decontamination & Reuse of Filtering Facepiece Respirators [Internet]. 2020 [cited 2020 Apr 14].

  2. Batelle. Final Report for the Bioquell Hydrogen Peroxide Vapor (HPV) Decontamination for Reuse of N95 Respirators [Internet]. Columbus; 2016.

  3. Kumar A, Kasloff S, Leung A, Cutts T, Strong J, Hills K, et al. N95 Mask Decontamination using Standard Hospital Sterilization Technologies. medRxiv [preprint]. [posted 2020 April 8; cited 2020 April 15].

Are there any updates on the efficacy of cloth masks?

  1. Leung NH, Chu DK, Shiu EY, Chan KH, McDevitt JJ, Hau BJ, Yen HL, Li Y, Ip DK, Peiris JM, Seto WH. Respiratory virus shedding in exhaled breath and efficacy of face masks. Nature Medicine. 2020 Apr 3:1-5.

  2. Davies A, Thompson K-A, Giri K, Kafatos G, Walker J, Bennett A. Testing the efficacy of homemade masks: Would they protect in an influenza pandemic? Disaster Med Public Health Prep. 2013;7(4):413–8.

  3. Neupane​ BB, Mainali S, Sharma A, Giri B. Optical microscopic study of surface morphology and filtering efficiency of face masks. PeerJ. 2019;7:e7142.

What have we learned from the COVID-19 outbreak in King County, Washington? Why are long term care facilities prone to COVID-19 outbreaks?
 

Answered in April 10, 2020 Newsletter

  • As discussed earlier (March 27th edition) long-term care facilities (LTCFs) are particularly at risk for COVID-19 outbreaks.(1,2)

  • During a COVID-19 outbreak in King County, Washington, USA, the index patient resided in a LTCF. 16 days after their diagnosis, 30% of residents in that facility tested positive for SARS-CoV-2, ~50% of whom were asymptomatic at time of testing.(3) The virus then spread to other facilities, resulting in a total of 167 positive cases.4 LTCF residents with confirmed COVID-19 had a hospitalization rate of 54.5% and fatality of 33.7%. In comparison, fatality rates were 6.2% among visitors, and 0% among health care workers.(4)

  • Some patients in this outbreak presented with few or atypical symptoms (e.g. malaise and nausea).(3)  Physicians must have a high index of suspicion in this population, and consider LTCF residence as a potential exposure. Rapid case identification can prompt infection control measures that limit further spread.   

  • An epidemiological investigation(4) identified factors that likely contributed to this outbreak:

    • Delayed recognition because COVID-19 was not suspected, was difficult to identify based on clinical features, and limited availability of testing.

    • Transfers of patients between facilities and staff working in multiple facilities.

    • Challenges to implementing infection control practices: inadequate supplies of PPE, poor familiarity with PPE, and poor adherence to PPE recommendations.

    • Some staff worked while symptomatic

  1. Lansbury LE, Brown CS, Nguyen-Van-Tam JS. Influenza in long-term care facilities. Influenza Other Respir Viruses [Internet]. 2017 09 [cited 2020 Apr 8];11(5):356-66.

  2. World Health Organization. Infection prevention and control guidance for long-term care facilities in the context of COVID-19: Interim guidance [Internet]. World Health Organization; 2020 Mar 21 [cited 2020 Apr 8].

  3. Kimball A, Hatfield KM, Arons M, James A, Taylor J, Spicer K, et al. Asymptomatic and Presymptomatic SARS-CoV-2 Infections in Residents of a Long-Term Care Skilled Nursing Facility —. MMWR Morb Mortal Wkly Rep. 2020;69(13):377–81.

  4. McMichael TM, Currie DW, Clark S, Pogosjans S, Kay M, Schwartz NG, et al. Epidemiology of Covid-19 in a Long-Term Care Facility in King County, Washington. N Engl J Med. 2020;1–7.

  5. Shared Health Manitoba (CA). COVID-19 highlights: Long term care [Internet]. Winnipeg MB: Shared Health Manitoba; 2020 Mar 27  [cited 2020 Apr 8].

Are surgical procedures in asymptomatic patients a risk for transmission of COVID-19? Can infection control measures limit this? How useful is screening or other measures to reduce transmission of COVID-19 in this setting?

Answered in April 10, 2020 Newsletter

  • Periprocedural transmission of SARS-CoV-2 to healthcare workers has likely occurred following C-section or lower-limb surgeries performed on COVID-19 positive patients from Wuhan, China who underwent spinal anaesthesia.(1) Further, it is known that patients without symptoms contribute to viral spread and can have viral loads similar to those with symptoms.(2)

  • Stringent and multi-faceted infection prevention and control measures can prevent perioperative viral transmission, even during high-risk procedures. Institutions that were able to protect all of their OR staff from contracting infections from infected surgical patients during the SARS epidemic attributed their success to: 1) enhanced personal protection (e.g. positive air-powered respirator for high-risk procedure or patient), 2) OR/ICU reorganization (e.g. geographic segregation, negative-pressure rooms, and minimizing staff involved), 3) minimizing intraoperative exposure to aerosolized secretions (e.g. surgical technique, reduced suction use), and 4) safe equipment disposal/decontamination.(3)

  • The choice of institutional strategies must take into account the local disease prevalence, testing capacity, and institutional capacity to implement preventative measures perioperatively:

    • Screening asymptomatic patients: CT scans and PCR tests will identify some patients without symptoms. However, currently no evidence confirms either their reliability in the setting of high disease prevalence, or their efficiency in the setting of low prevalence, when used for this purpose.

    • Universal use of enhanced infection and control measures: Routine implementation of comprehensive measures is resource-intensive and not feasible in all institutions.

    • Deferral of non-emergent surgery: Evidence from modeling studies suggests this may be effective. Additionally, observational data has raised the concern that asymptomatic SARS-CoV-2 positive patients who undergo surgery may develop worse COVID-19 related outcomes.(4,5)

  • Current guidelines for COVID-19 screening prior to essential surgeries in Manitoba can be found on the Shared Health website at under Resources for Specialty Areas – Surgery/Procedures. If possible, patients requiring non-emergent surgery should first undergo 14 days of self-isolation. If surgical patients are symptomatic, they are screened for COVID-19 using RT-PCR.

  1. Zhong Q, Liu YY, Luo Q, et al. Spinal anaesthesia for patients with coronavirus disease 2019 and possible transmission rates in anaesthetists: retrospective, single-centre, observational cohort study. [Internet] 2020 03 [cited 2020 Apr 8].

  2. Zou L, Ruan F, Huang M, Liang L, Huang H, Hong Z, et al. SARS-CoV-2 Viral Load in Upper Respiratory Specimens of Infected Patients. N Engl J Med. 2020;382(12):1177-1179.

  3. Tay JK, Khoo MLC, Loh WS. Surgical Considerations for Tracheostomy during the COVID-19 Pandemic: Lessons Learned from the Severe Acute Respiratory Syndrome Outbreak. JAMA Otolaryngology - Head and Neck Surgery. 2020.

  4. Zhang Y, Cheng SR. Estimating Preventable COVID19 Infections Related to Elective Outpatient Surgery in Washington State: A Quantitative Model. medRxiv. [preprint] 2020 Jan 1.

  5. Lei S, Jiang F, Su W, Chen C, Chen J, Mei W, Zhan LY, Jia Y, Zhang L, Liu D, Xia ZY. Clinical characteristics and outcomes of patients undergoing surgeries during the incubation period of COVID-19 infection. EClinicalMedicine. 2020 Apr 5:100331.

What strategies can be adopted to minimize the risk of secondary infections with respiratory viruses in household contacts?

Answered in April 3, 2020 Newsletter

  • Isolation of the index case within a separate room from other household members, keeping the room well-ventilated (open window, if possible, with a fan), flushing with the toilet lid closed, use of own personal products, and frequent hand washing have all been shown to reduce the risk of secondary household infection. Disinfection of shared surfaces may further reduce the risk. These interventions are most effective if implemented as soon as possible.(1,2)

  • Care of the index case should be provided by a single household caregiver to reduce household spread. If possible, choose a caregiver who is younger and does not have medical comorbidities.

  • Evidence is conflicting for the benefit of face masks worn by isolated cases or household contacts. Although some health agencies recommend the use of masks in this setting, other interventions should be prioritized given the current mask shortage. If you are going to wear a mask at home, be aware that mask changes and frequent adjustments may actually put you at increased risk, and hand washing around these moments is essential.(2)

  1. Zhang D, Liu W, Yang P, Zhang Y, Li X, Germ KE, Tang S, Sun W, Wang Q. Factors associated with household transmission of pandemic (H1N1) 2009 among self-quarantined patients in Beijing, China. PloS one. 2013;8(10).

  2. Wilson-Clark SD, Deeks SL, Gournis E, Hay K, Bondy S, Kennedy E, Johnson I, Rea E, Kuschak T, Green D, Abbas Z. Household transmission of SARS, 2003. Cmaj. 2006 Nov 7;175(10):1219-23.

What measures can healthcare workers undertake to minimize any risk of transmitting the infection to members of their household?

Answered in April 3 2020 Newsletter

  • Viral contamination of healthcare workers’ personal protective equipment (PPE), clothing, and skin can occur while caring for individuals with acute viral infections.(1) Doffing of PPE is one mechanism for viral transfer to skin and clothing.(2)

  • While the effectiveness of interventions (e.g. changing clothes or showering after a hospital shift) has not been investigated, some of these precautions were adopted during the SARS outbreak and may have contributed to lower rates of secondary infections in household contacts of healthcare workers.

  • In light of this, it is a reasonable precaution to develop a post-work routine that includes changing clothes before leaving work and showering upon arriving home.

  • Shared Health recommends changing clothes before going home, dedicating a pair of shoes for work only, and following normal laundry practices. (Shared Health MB Guidelines). 

  1. Phan L, Sweeney D, Maita D, Moritz D, Bleasdale S, Jones R. Respiratory viruses on personal protective equipment and bodies of healthcare workers. Infect Control Hosp Epidemiol. 2019;40(12):1356-1360.

  2. Casanova L, Alfano-Sobsey E, Rutala W, Weber D, Sobsey M. Virus transfer from personal protective equipment to healthcare employees’ skin and clothing. Emerging Infectious Diseases 2008;14(8):1291-1293.

What respirator should be used to care for patients with COVID-19? 

Answered in March 27, 2020 Newsletter

  • Procedure masks (“surgical face masks"), are effective for preventing diseases spread via droplets(1). Procedure masks are used for non-aerosol generating activities pertaining to the assessment and care of those affected by COVID-19. N95 respirators should be used ONLY during activities where aerosols are generated (click this link for list: AGMPs).

  • NOTE: Current Manitoba infection control guidelines suggest using enhanced droplet and contact precautions when caring for a patient with confirmed or suspected COVID-19; which includes gloves, a gown, and eye protection in addition to a face mask. 

 

  1. Long Y, Hu T, Liu L, Chen R, Guo Q, Yang L, Cheng Y, Huang J, Du L. Effectiveness of N95 respirators versus surgical masks against influenza: A systematic review and meta‐analysis. Journal of Evidence‐Based Medicine. 2020 Mar 13. 

  2. Advice on the use of masks in the community, during home care and in healthcare settings in the context of the novel coronavirus (COVID-19) outbreak [Internet]. World Health Organization. 2020 [cited 2020 Mar 25]. 

In the setting of a shortage of N95 respirators, can respiratory protection be used over extended periods of time?

Can they be re-used and/or sterilized?

Answered in March 27, 2020 Newsletter

  • Viral particles can persist on the surface of used procedure masks and N95 respirators. Removing a mask or respirator is a particularly high risk time for contaminating your hands.(1) However, the risk of re-aerosolizing particles from a mask to subsequent patients is low.

  • With repeated removal and reapplication, the fit and protection provided by an N95 respirator decreases. Masks and respirators that are obviously soiled are likely no longer effective.

  • At present, there is no well-studied and reliable method available to decontaminate standard surgical masks or respirators.

Key Points:

  1. Extending the use of a mask or respirator is preferred over repeated reuse, ie: it is preferable to leave the mask on for a longer period of time rather than removing and reusing it repeatedly.

  2. If a mask is visibly soiled it should be discarded.

  3.  Review proper technique for donning and doffing PPE – there is a high risk for health care workers to become exposed during this process.

  4. Review: https://professionals.wrha.mb.ca/old/extranet/ipc/ppe-videos.php

  5. If you inadvertently touch your mask or need to adjust it - properly clean your hands before and afterwards.

  1. Brady, T.M., Strauch, A.L., Almaguer, C.M., (...), Yorio, P.L., Fisher, E.M. Transfer of bacteriophage MS2 and fluorescein from N95 filtering facepiece respirators to hands: Measuring fomite potential. Journal of Occupational and Environmental Hygiene. 14(11), pp. 898-906. 

  2. Bergman MS, Viscusi DJ, Zhuang Z, Palmiero AJ, Powell JB, Shaffer RE. Impact of multiple consecutive donnings on filtering facepiece respirator fit. Am J Infect Control [Internet]. 2012;40(4):375–80. 

  3. Fisher EM, Shaffer RE. Considerations for recommending extended use and limited reuse of filtering facepiece respirators in health care settings. Vol. 11, Journal of Occupational and Environmental Hygiene.2014. 

  4. Recommended Guidance for Extended Use and Limited Reuse of N95 Filtering Facepiece Respirators in Healthcare Settings [Internet]. The National Institute for Occupational Safety and Health. 2018 [cited 2020 Mar 25].

  5. Strategies for Optimizing the Supply of Facemasks [Internet]. Centers for Disease Control and Prevention. 2020 [cited 2020 Mar 25].

  6. Mills D, Harnish DA, Lawrence C, Sandoval-Powers M, Heimbuch BK. Ultraviolet germicidal irradiation of influenza-contaminated N95 filtering facepiece respirators. Am J Infect Control [Internet]. 2018;46(7):e49–55. 

  7. Lore MB, Heimbuch BK, Brown TL, Wander JD, Hinrichs SH. Effectiveness of three decontamination treatments against influenza virus applied to filtering facepiece respirators. Ann Occup Hyg. 2012;56(1):92–101.

Are cloth masks safe to use? Are they as effective as medical masks in preventing infection?

Answered in March 27, 2020 Newsletter

  • Cloth masks have minimal to no protective benefits and only marginally prevent outward aerosol transmission. Compared to medical face masks, their use is associated with significantly higher rates of infection.(1)

  • Cloth masks should only be considered as a last resort, when no medical masks are available.

  1. Macintyre CR, Seale H, Dung TC, Hien NT, Nga PT, Chughtai AA, et al. A cluster randomised trial of cloth masks compared with medical masks in healthcare workers. BMJ Open. 2015;5(4):e006577. 

  2. Shakya KM, Noyes A, Kallin R, Peltier RE. Evaluating the efficacy of cloth facemasks in reducing particulate matter exposure. J Expo Sci Environ Epidemiol. 2017;27(3):352–7. 

  3. Davies A, Thompson K-A, Giri K, Kafatos G, Walker J, Bennett A. Testing the Efficacy of Homemade Masks: Would They Protect in an Influenza Pandemic? Disaster Med Public Health Prep. 2013;7(4):413–8.

  4. van der Sande M, Teunis P, Sabel R. Professional and Home-Made Face Masks Reduce Exposure to Respiratory Infections among the General Population. PLoS One. 2008;3(7):e2618.

What is the viability of coronavirus (SARS-COV-2) on surfaces?

Answered in March 21, 2020 Newsletter

  • As with other pathogens, viable viral particles can persist on surfaces such as stainless steel and plastics. Surface viability is lower on cardboard and copper.(1)

  • The exact persistence time depends on amount of virus, atmospheric conditions, and the surface.

  • Although surface contamination was a known contributor of nosocomial spread, earlier data of other similar coronaviruses suggests routine cleaning procedures and surface disinfectants are effective.(2,3)

  • Currently at our health care facilities, there is enhanced attention to housekeeping practices to ensure the safest possible environment for patients, staff and visitors.

 

Take home points:

  • (1) Follow all posted instructions for infection prevention and control (hand hygiene, personal protective equipment).

  • (2) When in doubt: wash your hands

1. van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, et al. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med [Internet]. 2020 Mar 17 [cited 2020 Mar 19];NEJMc2004973.

2. Chen Y-C, Huang L-M, Chan C-C, Su C-P, Chang S-C, Chang Y-Y, et al. SARS in Hospital Emergency Room. Emerg Infect Dis [Internet]. 2004 May 1 [cited 2020 Mar 19];10(5):782–8.

3. Kampf G, Todt D, Pfaender S, Steinmann E. Persistence of coronaviruses on inanimate surfaces and its inactivation with biocidal agents. Journal of Hospital Infection. 2020 Feb 6.

4. Lauer SA, Grantz KH, Bi Q, Jones FK, Zheng Q, Meredith HR, et al. The Incubation Period of Coronavirus Disease 2019 (COVID-19) From Publicly Reported Confirmed Cases: Estimation and Application. Ann Intern Med [Internet]. 2020 Mar 10 [cited 2020 Mar 19].

5. WHO. Considerations for quarantine of individuals in the context of containment for coronavirus disease (COVID-19) [Internet]. [cited 2020 Mar 19].