








key: cord-325598-gy809ee0
authors: Lyne, Cloutier; Natacha, Merindol; Geneviève, Pépin; Caroline, Marcoux-Huard; Pier-Alexandre, Vasil; Claudia, Houle; Shweta, Todkar; Marie-Claude, Lehoux; Nathalie, Houle; Hugo, Germain; Alexis, Danylo
title: Asymptomatic carriers of COVID-19 in a confined adult community population in Quebec: a cross-sectional study
date: 2020-08-21
journal: Am J Infect Control
DOI: 10.1016/j.ajic.2020.08.015
sha: 
doc_id: 325598
cord_uid: gy809ee0

Several countries have undertaken social distancing measures to stop SARS-CoV-2’ spread. Asymptomatic carriers’ prevalence is unknown and would provide essential information on hidden viral circulation. In our cross-sectional study, 1.82% of 330 asymptomatic confined individuals living in the community carried SARS-CoV-2 despite no contact with declared cases, raising concerns about unnoticed transmission.

Cloutier, Lyne 1 ; Merindol, Natacha 2,3 ; Pépin, Geneviève 4 ; Marcoux-Huard, Caroline 5 ; Vasil, Pier-Alexandre 5 ; Houle, Claudia 6, 7 ; Todkar, Shweta 1 ; Lehoux, Marie-Claude 3 ; Houle, Nathalie 1 ; Germain, Hugo 2,3 ; Danylo, Alexis 6  SARS-CoV-2 may spread asymptomatically in a population under social distancing restrictions.

As of August 9 th , nearly 20 million individuals contracted COVID-19 and about 720,000 died [1] . The United States counts for one fourth of these cases. SARS-CoV-2 transmission occurs principally through respiratory droplets or direct contact [2] . Viral load peaks before or at the time of symptoms onset, raising the possibility that presymptomatic people significantly contribute to viral spread [3, 4] . Other individuals remain asymptomatic despite viral detection, suggesting that they may participate in transmission [5] [6] [7] .

Studies conducted on individuals from the same households have convincingly shown that pre-symptomatic or asymptomatic SARS-CoV-2 carriers might transmit to their family members [8] [9] [10] . In a long-term care facility, 23 (30.3%) residents carried the virus, including 13 asymptomatic of the 76 that were tested [11] . An investigation on the Diamond Princess cruise ship in Japan identified 17.9% of SARS-CoV-2 infected cases as asymptomatic [12] . All these reports were carried out in a specific context of strong contacts between individuals.

Very few studies have assessed the proportion of asymptomatic individuals in the reality of a community that followed social distancing measures. In an isolated city of Italy, screening three thousand individuals lead to the identification of 88 carriers, including 50-75% of asymptomatic individuals [13, 14] . Nishiura Our cross-sectional study was held between April 14 th and 17 th , 2020 in the Mauricie region, Québec, Canada. We aimed to identify the proportion of asymptomatic carriers in a confined community of adults. The term confinement is used herein to reflect social restrictions instructed by Quebec's government, progressively implemented starting on March 11 th (Figure 1 ). On April 17 th , the last day of this study, 723 positive cases were identified for a total of 17,521 with a prevalence of 0.204% and an incidence of 0.008% in the Quebec's Province.

A total of 2250 employees between 18 and 69 years old from the Université du Québec Table 1 ). We (Table 1 ).

Our study identified 1,82% of asymptomatic carriers in a confined community. Their presence could be explained by 3 scenarios. First, they could be in fact presymptomatic individuals, as viral load peaks at the time of, or before symptoms onset [12, 19] . Our study was not designed to assess this possibility if symptoms developed later than 24 hours post-test. Second, following symptomatic infection, some cases experience prolonged viral nucleic acids detection by rRT-PCR [20] . Consequently, some individuals could be post-symptomatic cases with residual viral shedding that were not screened at the beginning of the pandemic.

The third possibility is true asymptomatic infection. The rate of this kind of infection is unknown. Pre-symptomatic people significantly contribute to viral spread, but we do not know if true asymptomatic and late post-symptomatic participate in transmission at this point. All positive cases had high C t values, which most probably reflects low viral shedding, although data are sparse on correlation between C t values and contagiousness.

1,82% of asymptomatic carriers is high when compared to the 0,204% prevalence.

However, there were 18.03% of carriers among the thousands of screened symptomatic individuals in the Province, ten times more than in our asymptomatic cohort. Our sample size is relatively small. At the time we designed our study, supplies in lab materials and staff availability were problematic, we chose a convenience sample size. Rates of asymptomatic carriers could be different in high-density urban area and in population with different socio-economic characteristics.

Despite its limitations, this is the first methodically designed study that evaluates the rate of asymptomatic carriers in a confined population. Six SARS-CoV-2 asymptomatic carriers that agreed with social distancing measures is a significant number and could suggest that prevalence is underestimated. This could represent ~100,000 asymptomatic carriers at the scale of the adult population of Quebec's Province at the time of this study. Interestingly, a preliminary analysis of the seroprevalence on 7,691 blood donors from Québec reported a similar rate of positivity [21] . Our results raise concerns about the possibility of viral spread through asymptomatic transmission, specifically in the context of an apprehended resurgence of SARS-CoV-2 infections following deconfinement. Since public health focuses on symptomatic cases, it is urgent to determine if asymptomatic cases contribute to transmission and to elucidate the dynamics of SARS-CoV-2 in distinct populations.

Seegene graciously offered lab test kits. The company was not involved in the study design nor in the data analysis. Internal research funds from UQTR. No external funding Legend: In the province of Quebec, the first case was declared on February 27 th . On March 11 th , travelers were isolated at home for 14 days upon return, gathering of more than 250 people were forbidden. On March 13 th , the health emergency state was declared. On March 14 th , non-essential visits to hospitals and long-term care facilities were prohibited. Between March 15 th and April 5 th , borders, public places, daycares, schools, businesses, non-essential services were closed, social distancing measures were implemented, gatherings of more than 5 individuals and travels between regions were prohibited. This study was conducted between April 14 th (612 positive cases on that day for a total of 14 860, a prevalence of 0,173% and an incidence of 0,007%) to April 17 th (723 positive cases for a total of 17521; a prevalence of 0,204% and an incidence of 0,008%) (data has been extracted from public health resources [22] ).

Graphical abstract. Asymptomatic frequency estimate during lockdown. * according to public data during the time of the study. Legend: Attitudes towards measures of social distancing and confinement were analysed through a Likert scale ranging from 1 to 7; 1 being complete agreement. Results presented in Table 1 show that very little variation in the scores, e.g. all participants being very much in agreement with the measures issued by the government during the two periods. The vast majority also stated that they were abiding by those rules. All differences noted between groups and within groups were not statistically significant.

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The research team wishes to acknowledge the Université du Québec à Trois-Rivières (UQTR) for providing human, financial and structural resources for the project and the Centre Intégré Universitaire de Santé et de Services Sociaux de la Mauricie et du Centre-Du-Québec (CIUSSS MCQ) for providing testing resources. We also thank participants and all volunteer nurses and personnel that worked at the clinic.

