The Canadian Pandemic Influenza Plan for the Health Sector, 2006
Dr. Theresa Tam and Karen Grimsrud, Co-Chairs
At the beginning of February I was surprised by Prime Minister Justin Trudeau’s assertions that it was safe to continue to fly to China, that we would only be testing those who self-reported symptoms, and that his plan for testing was science based. I was also surprised that Canada's Chief Public Health Officer Dr. Theresa Tam asserted that there was no risk from asymptomatic spreaders. It has come as no surprise to me that we have now closed our borders to China and most other countries, that we have stepped up our testing and begun contact tracing, and that studies have shown that asymptomatic spreading of COVID-19 is the norm.
I had six main reasons for objecting to Canada continuing passenger flights to China:
- First, we were the only country continuing to fly to China.
- Second, it was all over the news that by the time Wuhan was placed under quarantine over half the population of Wuhan had fled to other parts of China.
- Third, the virus had spread to many other parts of China, including most major cities, by February 1st
- Fourth, we were not testing people when they got on the planes in China for coronavirus, we were not testing the passengers when they disembarked from the planes, there were no penalties for breaking the quarantine, there no checks being made of the passengers to ensure that they were adhering to the quarantine, and there were no spot tests of the people coming from China. A few people arriving from China were advised to self-quarantine, but not everyone.
- Fifth, in November, 2014 during the Ebola crisis, Prime Minister Stephen Harper banned people from Ebola-stricken West Africa from traveling to Canada. As a consequence of his actions no Ebola case arose in Canada. The USA did not ban people from West Africa and confirmed a case of Ebola diagnosed in the United States in a man who traveled from West Africa to Dallas, Texas. That patient died. Earlier Saudi Arabia had announced a travel ban aimed at preventing Liberians, Sierra Leoneans and Guineans from visiting Islam's holy sites. No Ebola case arose in Saudi Arabia.
- Sixth, a ban works.
My main concern with Dr. Theresa Tam’s assertion that there was no risk from asymptomatic spreaders is that I have been aware of Typhoid Mary for over fifty-five years as she was often mentioned in side bars and fillers in newspapers when I was young. Typhoid Mary is the poster child for asymptomatic spreaders. Her real name was Mary Mallon. She was employed as a cook in various households and kitchens in the New York area over the period from 1907 to 1915. She was the first person in the United States identified as an asymptomatic carrier of typhoid fever and is believed to have infected 51 people, at least three of whom died. (Some estimates put the death total at fifty.) Eventually she was arrested and put in quarantine to stop her working and spreading the disease. Interestingly, Marineli et al. (2013) mention that “By the time she died New York health officials had identified more than 400 other healthy carriers of Salmonella typhi.”
Intriguingly there is a fair amount of information on diseases having been transmitted by asymptomatic carriers of diseases. In addition to typhoid, Wickipedia mentions C. difficile, influenzas, tuberculosis, and HIV. Transmission of diseases by asymptomatic carriers appears to be the norm, rather than the exception, for infectious diseases.
Dr. Theresa Tam stated that she followed and implemented The Canadian Pandemic Influenza Plan for the Health Sector , 2006 (“Canada’s Pandemic Plan”), of which she was the co-author. If she had followed the plan she should have noticed that “Transmission by asymptomatic persons is possible but it is more efficient when symptoms, such as coughing, are present and viral shedding is high (i.e. early in symptomatic period).” and that the “potential for asymptomatic infection and spread from asymptomatic individuals greatly limits the effectiveness and feasibility of most traditional public health control measures.”
In addition Health Canada distributed a publication in 2015 (updated in 2018) entitled ‘Canadian Pandemic Influenza Preparedness: Planning Guidance for the Health Sector” which mentions that “The pandemic virus will behave like seasonal influenza viruses in significant ways: ... Transmission is possible from asymptomatic persons but is greater when symptoms, such as coughing, are present and viral shedding is high (i.e., early in the symptomatic period).
If she had done a bit of research Dr. Tam might also have located an article by Fraser et al. (2004) discussing factors that make an infectious disease outbreak controllable, in which they argue that “Direct estimation of the proportion of asymptomatic and presymptomatic infections is achievable by contact tracing and should be a priority during an outbreak of a novel infectious agent.” noting that “no confirmed cases of transmission from asymptomatic patients have been reported to date in detailed epidemiological analyses of clusters of SARS cases, which suggests that, for SARS, there is a period after symptoms develop during which people can be isolated before their infectiousness increases. Actions taken during this period to isolate or quarantine ill patients can effectively interrupt transmission.” This is a warning that tests should be conducted for asymptomatic and presymptomatic infections.Dr. Tam might also have noted a paper by Myoung-don Oh et al. (2018) analyzing the 2015 MERS coronavirus outbreak in Korea in which they mention that “the potential for transmission from asymptomatic rRT-PCR positive individuals is still unknown. Therefore, asymptomatic [persons who test] positive for MERS-CoV should be isolated and should not return to work until two consecutive respiratory-tract samples test negative.”
Another paper that Dr. Tam might have located without much trouble is a 2018 report by the World Health Organization providing guidance for asymptomatic persons who test positive for Middle East respiratory syndrome coronavirus (MERS-CoV). She should have noted the paper in part because Katherine Defalco, Public Health Agency of Canada, Ottawa, Canada contributed to the WHO’s report. In this report WHO state that the potential for transmission from asymptomatic positive MERS-CoV persons is currently unknown but still recommended that “asymptomatic RT-PCR positive persons should be isolated , followed up daily for development of any symptoms and tested at least weekly – or earlier, if symptoms develop – for MERS-CoV. The place of isolation (hospital or home) shall depend on the health - care system’s isolation bed capacity, its capacity to monitor asymptomatic RT- PCR positive persons daily outside a health-care setting, and the conditions of the household and its occupants.” WHO also recommended that “When providing home isolation of asymptomatic RT-PCR positive persons, the person and family should be provided with clear instructions on:
• adequate physical separation from potential householdor social contacts, especially those with risk conditions for severe MERS-CoV illness (e.g. separate room and toilet);
• having food in the room and avoid sharing food or being in the same room with others as much as possible;
• avoidance of visitors and travel; ...
WHO also cautioned that “sometimes it is difficult to classify a case as ‘asymptomatic’ because although the person may not have any symptoms at the time of testing, he or she may develop illness during the course of infection.”
In contrast to WHO’s recommendations for asymptomatic MERS-CoV coronavirus persons, Canada did no testing to find asymptomatic COVID-19 coronavirus carriers. Instead we were told that they posed no threat, and that it was only those that developed symptoms who required testing. As noted above, recent studies have shown that asymptomatic spreading of COVID-19 is the norm. More importantly, Lai et al. (2020) report that “the transmission of COVID-19 through asymptomatic carriers via person-to-person contact was observed in many reports” citing reports published on the web by Rothe on January 30, 2020; by Liu on February 12, 2020; by Yu on February 18; and by Bai on February 21, 2020. Surprisingly, despite these warnings no effort was made in Canada in February or March to test for asymptomatic carriers. In fact, we still don’t test for asymptomatic carriers.
There have been further reports of asymptomatic spreading. On March 23 Qian et al. reported a COVID-19 family cluster in China caused by a presymptomatic case. On April 1st Wei et al, reported on an investigation of all 243 cases of COVID-19 reported in Singapore during January 23–March 16 and identified seven clusters of cases in which presymptomatic transmission is the most likely explanation for the occurrence of secondary cases. Ten of the cases within these clusters were attributed to presymptomatic transmission and accounted for 6.4% of the 157 locally acquired cases reported as of March 16.
Dr. Tam was on the CBC News the other night reporting that only ten cases in Canada could be traced to origins in China. However, we only tested those who self-reported symptoms. As we never tested for asymptomatic spreaders , we will never know how many asymptomatic spreaders from China (or other countries) were in Canada. Further, we have only traced a fraction of those who have developed the disease, and will only know that many people contracted the disease while in Canada, without knowing the source for their disease. By April 29th Health Canada, for confirmed cases of COVID-19, was able to trace the travel history (location travelled to) of only 1,201 cases in Ontario out of 16,000 confirmed cases; and 1,032 cases in Quebec out of 28,000 confirmed cases. The vast majority of cases are allocated simply to community spread without knowing the source and with no way of knowing whether the source was an asymptomatic spreader.
Christopher Brett
Ottawa
Added May 15 -17, 2020: There are other earlier papers that warn against asymptomatic spreading of coronavirus. For example, Dave Cavanagh (2003) reviewed attenuated vaccines and inactivated vaccines developed for a coronavirus that affects chickens to forecast the development of vaccines for use against the SARS coronavirus, and commented with respect to possible SARS vaccines that “Application of a SARS vaccine is perhaps best limited to a minimal number of targeted individuals who can be monitored, as some vaccinated persons might, if infected by SARS coronavirus, become asymptomatic excretors of virus, thereby posing a risk to non-vaccinated people.” and that “Coronaviruses can establish persistent infections, in at least a proportion of their hosts, resulting in chronic asymptomatic shedders, with subsequent problems for containment of the disease.”
Another early paper was by Che et al. (2006) who reported “An asymptomatic case of severe acute respiratory syndrome (SARS) occurred early in 2004, during a community outbreak of SARS in Guangzhou, China.”
Dr. Paul Auwaerter, M.D. of John Hopkins University has commented (last updated May 13) for COVID-19 that ‘Viral shedding by asymptomatic people may represent 25–50% of total infections.’ noting that “Why widespread and rapid transmission occurs is not completely certain, and is provoking changes in public health recommendations as well as anxieties. Asymptomatically infected people who shed and spread is a likely explanation.”
Timeline for Mentions of Aymptomatic and Presymptomatic Spreading
January 26, 2020
China's health minister Ma Xiaowei states that people can spread the Wuhan coronavirus before they become symptomatic. [Elizabeth Cohen, CNN, Sunday, January 26, 2020]
January 29, 2020
Theresa Tam appears before Canada’s Standing Committee on Health and states:
-“For other completely asymptomatic people, currently there's no evidence that we should be quarantining them.”
-“We do know that asymptomatic people are not the key driver of epidemics. That is very important to understand.”
- “I know that the World Health Organization is actively in China looking at the evidence. That is a very key piece of evidence that we are trying to ascertain. We do know something about coronaviruses, given that we've had other coronaviruses that cause anything from a mild illness through the common cold all the way to a more severe end of the spectrum such as SARS, the coronavirus and MERS, or Middle East respiratory syndrome coronavirus. Based on what we know about those coronaviruses, is it possible that an asymptomatic person could transmit the virus? Even if it's possible, it is, we believe, a rare event. It is not that type of transmission that drives the force of an epidemic.”
January 30, 2020
The Honorable Patty Hajdu (Liberal Member of Parliament ) tells Parliament: “Mr. Speaker, it is really important that we remember there is a difference between quarantine and isolation. If people are sick, they need to be in isolation to prevent the spread of illness, because the spread of illness is transmitted through droplets. Quarantine is used when there are people that are asymptomatic. Right now, what we know about the virus is that it cannot be transmitted while people are asymptomatic.”
January 30, 2020
German researchers (Rothe et al.) pre-release a report of a case of 2019-nCoV infection acquired outside Asia in which transmission appears to have occurred during the incubation period, entitled ‘Transmission of 2019-nCoV Infection from an Asymptomatic Contact in Germany.’
(Later published March 5, 2020 New England Journal of Medicine 2020; 382:970-971]
January 31, 2020
Dr. Anthony Fauci says a new study published Thursday night shows people can spread the Wuhan coronavirus before symptoms set in. In this report German researchers found that the virus was transmitted by people without symptoms in five instances in one cluster of people: from a parent to a daughter; from that daughter to two colleagues; and from one of those colleagues to two other coworkers. "There's no doubt after reading this paper that asymptomatic transmission is occurring," said Dr. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases. "This study lays the question to rest."[see Elizabeth Cohen and John Bonifield, CNN, Friday, January 31, 2020]
February 1, 2020
WHO issues Novel Coronavirus (2019 - nCoV) Situation Report 12 which states “The main driver of transmission, based on currently available data, is symptomatic cases . WHO is aware of possible transmission of 2019- nCoV from infected people before they developed symptoms. Detailed exposure histories are being taken to better understand the pre-clinical phase of infection and how transmission may have occurred in these few instances. Asymptomatic infection may be rare, and transmission from an asymptomatic person is very rare with other coronaviruses, as we have seen with Middle East Respiratory Syndrome coronavirus . Thus, transmission from asymptomatic cases is likely not a major driver of transmission. Persons who are symptomatic will spread the virus more readily through coughing and sneezing.
February 5, 2020
Canada’s Standing Committee on Health – Mr. Don Davies (MP, NDP), states “The World Health Organization's February 1 situation report on the novel coronavirus stated, “WHO is aware of possible transmission of 2019-nCoV from infected people before they developed symptoms.” An early study on asymptomatic transmission of the virus published last week in the New England Journal of Medicine also appeared to confirm that asymptomatic transmission is possible.” and asks Dr. Tam “How does the existence of asymptomatic transmission change your approach to containing this virus, if at all?”
Theresa Tam replied (2020-02-05 16:18): “ We are aware of a very small number of case reports in which it's suspected that asymptomatic transmission may have occurred, but these have not been verified. In fact, with regard to the New England Journal study, there's now been a publication to say that it was incorrect and that this person was, in fact, symptomatic and had been taking some medication that suppressed his fever, for example. That's a very important fact to verify and correct. I'm very happy that German scientists and WHO have verified that.
We have heard other potential reports, which have not been substantiated. What we know is that it could possibly happen, but we think it would be rare and very unlikely that asymptomatic persons would be the key driver of an actual outbreak or epidemic.”
February 5, 2020
Canada’s Standing Committee on Health –
Ms. Jenny Kwan (MP, Vancouver East, NDP): “The Minister of Health said in the House last week that those who are asymptomatic cannot spread the virus. I'm glad to hear the additional information from WHO. It seems to verify that, at least to that extent.... However, the Minister of Health in China has been reported as saying that it can spread asymptomatically. My question, then, is this. Have we contacted China directly to ask this question for clarification? As was acknowledged last week by the panel, China has the foremost knowledge about the virus. Can we not contact China directly to verify that information? It seems to me that it is a critical question that we should have a definitive answer on.”
March 30, 2020
Dr. Theresa Tam: "Putting a mask on an asymptomatic person is not beneficial, obviously, if you're not infected,"
March 31, 2020
Evan Dyer CBC News Posted: Mar 31, 2020: “Dr. K.K. Cheng, director of the Institute of Applied Health Research at the University of Birmingham in the U.K., said that Tam's advice makes a dangerous assumption — that an asymptomatic person is not a spreader. "The important thing about this coronavirus is that some patients start to shed virus, and become infectious, even before they have symptoms," he said. "In public health, a principle is we try to limit the source of harmful exposures rather than do mitigation, if we can.”“
April 2, 2020
The World Health Organization releases Coronavirus disease 2019 (COVID-19) Situation Report – 73, which comments on Pre-symptomatic and Asymptomatic transmission.
Pre-symptomatic transmission: The incubation period for COVID -19, which is the time between exposure to the virus (becoming infected) and symptom onset, is on average 5 - 6 days, however can be up to 14 days. During this period, also known as the “pre- symptomatic” period, some infected persons can be contagious. Therefore, transmission from a pre-symptomatic case can occur before symptom onset. In a small number of case reports and studies, pre-symptomatic transmission has been documented through contact tracing efforts and enhanced investigation of clusters of confirmed cases. [12 - 17] This is supported by data suggesting that some people can test positive for COVID-19 from 1 - 3 days before they develop symptoms. [6,16] Thus, it is possible that people infected with COVID-19 could transmit the virus before significant symptoms develop. It is important to recognize that pre-symptomatic transmission still requires the virus to be spread via infectious droplets or through touching contaminated surfaces.
Asymptomatic transmission: An asymptomatic laboratory - confirmed case is a person infected with COVID - 19 who does not develop symptoms. Asymptomatic transmission refers to transmission of the virus from a person, who does not develop symptoms . There are few reports of laboratory - confirmed cases who are truly asymptomatic, and to date, there has been no documented asymptomatic trans mission. This does not exclude the possibility that it may occur. Asymptomatic cases have been reported as part of contact tracing efforts in some countries. WHO regularly monitors all emerging evidence about this critical topic and will provide an upda te as more information becomes available
April 3, 2020
Karina Roman CBC News: Mounting evidence of COVID-19 'silent spreaders' contradicts government's earlier messages: “[A] growing body of research indicates [Dr. Theresa Tam and Health Minister Patty Hajdu] were wrong. In fact, people don't have to appear ill at all to infect others. Jeffrey Shaman, a professor of environmental health sciences at Columbia University in New York, says he is frustrated when people deny that asymptomatic spread can happen. "We have so much evidence that that is going on," he said. "It's ridiculous." It remains unclear if understanding the threat earlier might have affected policy. Had the threat been fully realized, different decisions might have been made regarding travel restrictions, quarantines and physical distancing. Shaman and other researchers argue that even two months ago, officials like Tam and Hajdu should have been more open to the possibility of asymptomatic transmission, considering by that point there was a flurry of research being undertaken by scientists racing to understand how the virus was spreading so fast and far. Many of those researchers suspected asymptomatic transmission.”
Thursday, April 23, 2020
Standing Committee on Procedure and House Affairs
Hon. Kirsty Duncan: Is asymptomatic spread of COVID-19 possible, yes or no?
Dr. Barbara Raymond: Yes, it is possible. We do not know the degree to which it is driving the epidemic, but we do believe it to be possible. In addition to that, pre-symptomatic spread, through people who are infectious before they are aware that they are ill, is also a significant concern
++++++++++++++++++
Cavanagh, Dave, 2003
Severe Acute Respiratory Syndrome Vaccine Development: Experiences of Vaccination Against Avian Infectious Bronchitis Coronavirus. Avian Pathol . 2003 Dec;32(6):567-82.
doi: 10.1080/03079450310001621198. https://pubmed.ncbi.nlm.nih.gov/14676007/
https://www.tandfonline.com/doi/full/10.1080/03079450310001621198
Paul G. Auwaerter, M.D., Updated: May 13, 2020
Coronavirus COVID-19 (SARS-CoV-2). Johns Hopkins ABX Guide,
https://www.hopkinsguides.com/hopkins/view/Johns_Hopkins_ABX_Guide/540747/all/Coronavirus_COVID_19__SARS_CoV_2_
Xiao-yan Che, Biao Di, Guo-ping Zhao, Ya-di Wang, Li-wen Qiu, Wei Hao, Ming Wang, Peng-zhe Qin, Yu-fei Liu, Kwok-hong Chan et al., 2006
A Patient with Asymptomatic Severe Acute Respiratory Syndrome (SARS) and Antigenemia from the 2003–2004 Community Outbreak of SARS in Guangzhou, China. Clinical Infectious Diseases, Volume 43, Issue 1, 1 July 2006, Pages e1–e5, https://doi.org/10.1086/504943
https://academic.oup.com/cid/article/43/1/e1/310697
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References and Suggested Reading
Anonymous, 2003
Learning from SARS - Renewal of Public Health in Canada. A report of the National Advisory Committee on SARS and Public Health October 2003. 234 pages https://www.phac-aspc.gc.ca/publicat/sars-sras/pdf/sars-e.pdf
Anonymous, 2015
Canadian Pandemic Influenza Preparedness: Planning Guidance for the Health Sector. Health Canada, 60 pages
https://www.phac-aspc.gc.ca/cpip-pclcpi/assets/pdf/report-rapport-2015-eng.pdf
Anonymous, 2018
Canadian Pandemic Influenza Preparedness: Planning Guidance for the Health Sector. Health Canada, 64 pages
https://www.canada.ca/content/dam/phac-aspc/migration/phac-aspc/cpip-pclcpi/assets/pdf/report-rapport-02-2018-eng.pdf
Anonymous, 2020a
Asymptomatic carrier
https://en.wikipedia.org/wiki/Asymptomatic_carrier
Anonymous, 2020b
Mary Mallon
https://en.wikipedia.org/wiki/Mary_Mallon
Anonymous, 2020c
Subclinical infection
https://en.wikipedia.org/wiki/Subclinical_infection#List_of_subclinical_infections
Y. Bai, L. Yao, T. Wei, F. Tian, D.Y. Jih, L. Chen, et al., 2020 Feb 21
Presumed asymptomatic carrier transmission of COVID-19
J Am Med Assoc (2020 Feb 21), 10.1001/jama.2020.2565
Filio Marineli, Gregory Tsoucalas, Marianna Karamanou, and George Androutsos, 2013
Mary Mallon (1869-1938) and the history of typhoid fever. Ann Gastroenterol. 2013; 26(2): 132–134. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3959940/
Fraser C, Riley S, Anderson R et al. 2004
Factors that make an infectious disease outbreak controllable. Proc Natl Acad Sci USA 2004;101(16):6146–51.
https://www.pnas.org/content/101/16/6146
Lai, Chih-Cheng; Liu, Yen Hung; Wang, Cheng-Yi; Wang, Ya-Hui; Hsueh, Shun-Chung; Yen, Muh-Yen; Ko, Wen-Chien; Hsueh, Po-Ren (2020-03-04).
Asymptomatic carrier state, acute respiratory disease, and pneumonia due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2): Facts and myths". Journal of Microbiology, Immunology and Infection. doi:10.1016/j.jmii.2020.02.012. ISSN 1684-1182.
Y.C. Liu, C.H. Liao, C.F. Chang, C.C. Chou, Y.R. Lin , 2020 Feb 12
A locally transmitted case of SARS-CoV-2 infection in Taiwan.
New England J Med (2020 Feb 12), 10.1056/NEJMc2001573
Myoung-don Oh, Wan Beom Park, Sang-Won Park, Pyoeng Gyun Choe, Ji Hwan Bang, Kyoung-Ho Song, Eu Suk Kim, Hong Bin Kim, and Nam Joong Kim, 2018
Middle East respiratory syndrome: what we learned from the 2015 outbreak in the Republic of Korea. Korean J Intern Med. 2018 Mar; 33(2): 233–246.
Published online 2018 Feb 27. doi: 10.3904/kjim.2018.031
Qian G, Yang N, Ma AHY, et al. Epub March 23, 2020
A COVID-19 Transmission within a family cluster by presymptomatic infectors in China. Clin Infect Dis 2020. https://www.ncbi.nlm.nih.gov/pubmed/32201889
C. Rothe, M. Schunk, P. Sothmann, G. Bretzel, G. Froeschl, C. Wallrauch, et al. (2020 Jan 30)
Transmission of 2019-nCoV infection from an asymptomatic contact in Germany
N Engl J Med, 10.1056/NEJMc2001468
Theresa Tam and Karen Grimsrud, Co-Chairs, 2006
The Canadian Pandemic Influenza Plan for the Health Sector. Public Health Agency of Canada.
550 pages. https://www.longwoods.com/articles/images/Canada_Pandemic_Influenza.pdf
W. E. Wei; , Z. Li; C. J. Chiew, S. E. Yong, M. P. Toh, V. J. Lee, 2020, April 10& April 1
Presymptomatic Transmission of SARS-CoV-2 — Singapore, January 23–March 16, 2020
Morbidity and Mortality Weekly Report (MMWR), 69(14);411–415. On April 1, 2020, this report was posted online as an MMWR Early Release.
https://www.cdc.gov/mmwr/volumes/69/wr/mm6914e1.htm
World Health Organization, 2018
Management of asymptomatic persons who are RT-PCR positive for Middle East respiratory syndrome coronavirus (MERS-CoV): Interim guidance . 3 January 2018
WHO/MERS/IPC/15.2 Rev.1 Geneva:
http://apps.who.int/iris/bitstream/10665/180973/1/WHO_MERS_IPC_15.2_eng.pdf?ua=1&ua=1
P. Yu, J. Zhu, Z. Zhang, Y. Han, L. Huang, 2020 Feb 18
A familial cluster of infection associated with the 2019 novel coronavirus indicating potential person-to-person transmission during the incubation period
J Infect Dis (2020 Feb 18), 10.1093/infdis/jiaa077
Peter Zimonjic, Rosemary Barton, Philip Ling, 2020
'Was it perfect? No': Theresa Tam discusses Canada's early pandemic response. 'Could we have done more at the time? You can retrospectively say yes,' Canada's top doctor says CBC News Posted: Apr 27, 2020 5:29 PM ET | Last Updated: April 28
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