COVID-19 Case Age Distribution: Correction for Differential Testing by Age.

BACKGROUND: Despite expected initial universal susceptibility to a novel pandemic pathogen like SARS-CoV-2, the pandemic has been characterized by higher observed incidence in older persons and lower incidence in children and adolescents. OBJECTIVE: To determine whether differential testing by age group explains observed variation in incidence. DESIGN: Population-based cohort study. SETTING: Ontario, Canada. PARTICIPANTS: Persons diagnosed with SARS-CoV-2 and those tested for SARS-CoV-2. MEASUREMENTS: Test volumes from the Ontario Laboratories Information System, number of laboratory-confirmed SARS-CoV-2 cases from the Integrated Public Health Information System, and population figures from Statistics Canada. Demographic and temporal patterns in incidence, testing rates, and test positivity were explored using negative binomial regression models and standardization. Sources of variation in standardized ratios were identified and test-adjusted standardized infection ratios (SIRs) were estimated by metaregression. RESULTS: Observed disease incidence and testing rates were highest in the oldest age group and markedly lower in those younger than 20 years; no differences in incidence were seen by sex. After adjustment for testing frequency, SIRs were lowest in children and in adults aged 70 years or older and markedly higher in adolescents and in males aged 20 to 49 years compared with the overall population. Test-adjusted SIRs were highly correlated with standardized positivity ratios (Pearson correlation coefficient, 0.87 [95% CI, 0.68 to 0.95]; P < 0.001) and provided a case identification fraction similar to that estimated with serologic testing (26.7% vs. 17.2%). LIMITATIONS: The novel methodology requires external validation. Case and testing data were not linkable at the individual level. CONCLUSION: Adjustment for testing frequency provides a different picture of SARS-CoV-2 infection risk by age, suggesting that younger males are an underrecognized group at high risk for SARS-CoV-2 infection. PRIMARY FUNDING SOURCE: Canadian Institutes of Health Research.

Quantifying contact patterns in response to COVID-19 public health measures in Canada.

BACKGROUND: A variety of public health measures have been implemented during the COVID-19 pandemic in Canada to reduce contact between individuals. The objective of this study was to provide empirical contact pattern data to evaluate the impact of public health measures, the degree to which social contacts rebounded to normal levels, as well as direct public health efforts toward age- and location-specific settings. METHODS: Four population-based cross-sectional surveys were administered to members of a paid panel representative of Canadian adults by age, gender, official language, and region of residence during May (Survey 1), July (Survey 2), September (Survey 3), and December (Survey 4) 2020. A total of 4981 (Survey 1), 2493 (Survey 2), 2495 (Survey 3), and 2491 (Survey 4) respondents provided information about the age and setting for each direct contact made in a 24-h period. Contact matrices were constructed and contacts for those under the age of 18 years imputed. The next generation matrix approach was used to estimate the reproduction number (Rt) for each survey. Respondents with children under 18 years estimated the number of contacts their children made in school and extracurricular settings. RESULTS: Estimated Rt values were 0.49 (95% CI: 0.29-0.69) for May, 0.48 (95% CI: 0.29-0.68) for July, 1.06 (95% CI: 0.63-1.52) for September, and 0.81 (0.47-1.17) for December. The highest proportion of reported contacts occurred within the home (51.3% in May), in 'other' locations (49.2% in July) and at work (66.3 and 65.4% in September and December). Respondents with children reported an average of 22.7 (95% CI: 21.1-24.3) (September) and 19.0 (95% CI 17.7-20.4) (December) contacts at school per day per child in attendance. CONCLUSION: The skewed distribution of reported contacts toward workplace settings in September and December combined with the number of reported school-related contacts suggest that these settings represent important opportunities for transmission emphasizing the need to support and ensure infection control procedures in both workplaces and schools.

The Prevalence of Campylobacter in Live Cattle, Turkey, Chicken, and Swine in the United States and Canada: A Systematic Review and Meta-Analysis.

Campylobacter cause gastroenteritis in humans and may be shed in the feces of livestock and poultry species, including cattle, chicken, turkey, and swine. However, a synthesis of the prevalence on farms in the United States and Canada is currently lacking. Thus, our objective was to conduct a systematic review and meta-analysis to estimate the prevalence of Campylobacter coli, Campylobacter jejuni, and Campylobacter spp. on livestock and poultry farms operated under commercial conditions in the United States and Canada. The relevant literature was identified and examined for eligibility based on a priori inclusion and exclusion criteria. Relevant data were extracted, and a meta-analysis was performed. The data were transformed using the Freeman-Tukey arcsine transformation to stabilize the variance. A separate meta-analysis was performed for each animal species, level of sampling (individual versus pooled), and species of Campylobacter, for a total of 29 meta-analyses. C. jejuni and Campylobacter spp. were present in all livestock and poultry species of interest, whereas C. coli was found in all species of interest with the exception of chickens. Furthermore, substantial heterogeneity was observed in most meta-analyses. In an attempt to account for this, subgroup analyses were performed on potential moderators. However, with the exception of beef cattle, where studies in feedlot cattle reported a consistently higher prevalence compared with adult cattle on pasture, significant heterogeneity remained in the majority of meta-analyses after accounting for potential moderators. The results of this review can be used to inform future risk assessment, consumer and producer awareness, and resource allocation, and identify gaps for future research.

Diagnostic testing patterns for Streptococcus equi subsp. equi in Ontario horses during the years 2008 to 2018.

This retrospective study describes testing patterns and the incidence of Streptococcus equi subsp. equi in Ontario to assess the utility of laboratory data for surveillance purposes. Laboratory records for equine infectious disease test submissions were extracted from the Animal Health Laboratory (AHL) at the University of Guelph for the years 2008 to 2018. Yearly and seasonal trends in S. equi testing and the proportion of tests that returned positive results were assessed. The number of samples submitted for S. equi testing decreased over the 11-year period (odds ratio = 0.96, 95% confidence interval: 0.92 to 0.999; P = 0.04). A generalized linear model identified a significant seasonal effect for animals recognized as clinically ill, with the highest test positivity noted in the winter. Although this study identified important trends in the incidence of S. equi in Ontario, the variability in information accompanying test submissions made the data challenging to interpret, highlighting the need for more complete diagnostic submission data for S. equi.

Tendance des tests diagnostiques pour Streptococcus equi subsp. equi chez les chevaux de l'Ontario au cours des années 2008 à 2018. Cette étude rétrospective décrit les tendances des test et l'incidence de Streptococcus equi subsp. equi en Ontario pour évaluer l'utilité des données de laboratoire à des fins de surveillance. Les dossiers de laboratoire pour les soumissions de tests de maladies infectieuses équines ont été extraits des données du Animal Health Laboratory (AHL), University of Guelph pour les années 2008 à 2018. Les tendances annuelles et saisonnières des tests de S. equi et la proportion de tests qui ont donné des résultats positifs ont été évaluées. Le nombre d'échantillons soumis pour la recherche de S. equi a diminué au cours de la période de 11 ans (rapport de cotes = 0,96, intervalle de confiance à 95% : 0,92 à 0,999; P = 0,04). Un modèle linéaire généralisé a identifié un effet saisonnier significatif pour les animaux reconnus comme cliniquement malades, la positivité de test la plus élevée étant notée en hiver. Bien que cette étude ait identifié des tendances importantes dans l'incidence de S. equi en Ontario, la variabilité des informations accompagnant les soumissions a rendu les données difficiles à interpréter, soulignant le besoin de données plus complètes lors de soumission pour le diagnostic S. equi.(Traduit par Dr Serge Messier).

A within-host mathematical model of H9N2 avian influenza infection and type-I interferon response pathways in chickens.

Chickens infected with avian influenza virus (AIV) transmit the virus via respiratory and cloacal shedding. While previous mathematical models have shown that the innate immune response is necessary for the early suppression of virus production in infected respiratory cells, the different pathways by which the innate immune response can affect cloacal viral shedding have not been studied in chickens. The present study aims to evaluate the sensitivity of H9N2 low pathogenic AIV shedding in chicken gastrointestinal cells to different type-I interferon (IFN) response pathways, and to determine the impact of a cellular eclipse phase (latent period) on the time to peak virus shedding using a mathematical model describing within host viral kinetics. Our model results demonstrate that a mechanistic model that incorporates 1) the intracellular antiviral effects of type-I IFN on virus production, 2) destruction of infected cells by type-I IFN activated Natural Killer cells, and 3) an eclipse phase is most consistent with experimental cloacal virus shedding data. These results provide a potential mechanistic explanation for the delay to peak cloacal virus shedding observed in experimental studies conducted in chickens, as well as an improved understanding of the primary type-I IFN pathways involved in the control of cloacal virus shedding, which may lead to the development of more targeted vaccine candidates.

Mathematical modelling of COVID-19 transmission and mitigation strategies in the population of Ontario, Canada.

BACKGROUND: Physical-distancing interventions are being used in Canada to slow the spread of severe acute respiratory syndrome coronavirus 2, but it is not clear how effective they will be. We evaluated how different nonpharmaceutical interventions could be used to control the coronavirus disease 2019 (COVID-19) pandemic and reduce the burden on the health care system. METHODS: We used an age-structured compartmental model of COVID-19 transmission in the population of Ontario, Canada. We compared a base case with limited testing, isolation and quarantine to scenarios with the following: enhanced case finding, restrictive physical-distancing measures, or a combination of enhanced case finding and less restrictive physical distancing. Interventions were either implemented for fixed durations or dynamically cycled on and off, based on projected occupancy of intensive care unit (ICU) beds. We present medians and credible intervals from 100 replicates per scenario using a 2-year time horizon. RESULTS: We estimated that 56% (95% credible interval 42%-63%) of the Ontario population would be infected over the course of the epidemic in the base case. At the epidemic peak, we projected 107 000 (95% credible interval 60 760-149 000) cases in hospital (non-ICU) and 55 500 (95% credible interval 32 700-75 200) cases in ICU. For fixed-duration scenarios, all interventions were projected to delay and reduce the height of the epidemic peak relative to the base case, with restrictive physical distancing estimated to have the greatest effect. Longer duration interventions were more effective. Dynamic interventions were projected to reduce the proportion of the population infected at the end of the 2-year period and could reduce the median number of cases in ICU below current estimates of Ontario's ICU capacity. INTERPRETATION: Without substantial physical distancing or a combination of moderate physical distancing with enhanced case finding, we project that ICU resources would be overwhelmed. Dynamic physical distancing could maintain health-system capacity and also allow periodic psychological and economic respite for populations.

Descriptive network analysis of a Standardbred horse training facility contact network: Implications for disease transmission.

Infectious respiratory disease is a common cause of morbidity among racehorses. Quantification of contact patterns in training facilities could help inform disease prevention strategies. The study objectives were to: i) describe the contact network among horses, locations, and humans at a Standardbred horse training facility in Ontario; ii) describe the characteristics of highly influential individuals; and iii) investigate how management changes alter the network metrics and discuss the potential implications for disease transmission. Proximity loggers detected contacts among horses, staff, and locations (n = 144). Network metrics and node centrality measures were described for a 2-mode and horse-only contact network. The 2-mode network density was 0.16. and the median node degree was 20 [interquartile range (IQR) = 12 to 27]. Yearlings and floating staff were most influential in the network suggesting biosecurity programs should emphasize reducing contacts in these groups. Removing highly influential staff or co-housing of age groups resulted in changes to network diameter and density.

Analyse descriptive du réseau de contacts d'un centre d'entraînement de chevaux Standardbred : Implications pour la transmission de maladies. Les maladies respiratoires infectieuses sont une cause commune de morbidité parmi les chevaux de course. Une quantification des patrons de contact dans les centres d'entraînement pourrait aider à avoir des stratégies appropriées de prévention des maladies. Les objectifs de la présente étude étaient de : i) décrire le réseau des contacts entre les chevaux, les localisations et les humains à un centre d'entraînement pour chevaux Stadardbred en Ontario; ii) décrire les caractéristiques d'individus très influents; iii) examiner comment les changements de gestion altèrent le réseau des systèmes de mesure et discuter les implications potentielles pour la transmission des maladies. Des enregistreurs de proximité détectèrent les contacts parmi les chevaux, le personnel et les localisations (n = 144). Les systèmes de mesure et les mesures de centralité des noeuds furent décrits pour un réseau à 2 modes et un réseau de contact entre chevaux uniquement. La densité du réseau à 2 modes était de 0,16 et le degré médian du noeud était 20 [écart interquartile (IQR) = 12 à 27]. Les yearlings et le personnel occasionnel étaient les plus influents dans le réseau suggérant que les programmes de biosécurité devraient mettre l'emphase sur une réduction des contacts dans ces groupes. Le retrait de personnel très influent ou cohabitation de groupes d'âge a résulté en des changements dans le diamètre et la densité du réseau.(Traduit par Dr Serge Messier).

A case-crossover analysis of the impact of weather on primary cases of Middle East respiratory syndrome.

BACKGROUND: Middle East respiratory syndrome coronavirus (MERS-CoV) is endemic in dromedary camels in the Arabian Peninsula, and zoonotic transmission to people is a sporadic event. In the absence of epidemiological data on the reservoir species, patterns of zoonotic transmission have largely been approximated from primary human cases. This study aimed to identify meteorological factors that may increase the risk of primary MERS infections in humans. METHODS: A case-crossover design was used to identify associations between primary MERS cases and preceding weather conditions within the 2-week incubation period in Saudi Arabia using univariable conditional logistic regression. Cases with symptom onset between January 2015 - December 2017 were obtained from a publicly available line list of human MERS cases maintained by the World Health Organization. The complete case dataset (N = 1191) was reduced to approximate the cases most likely to represent spillover transmission from camels (N = 446). Data from meteorological stations closest to the largest city in each province were used to calculate the daily mean, minimum, and maximum temperature (οC), relative humidity (%), wind speed (m/s), and visibility (m). Weather variables were categorized according to strata; temperature and humidity into tertiles, and visibility and wind speed into halves. RESULTS: Lowest temperature (Odds Ratio = 1.27; 95% Confidence Interval = 1.04-1.56) and humidity (OR = 1.35; 95% CI = 1.10-1.65) were associated with increased cases 8-10 days later. High visibility was associated with an increased number of cases 7 days later (OR = 1.26; 95% CI = 1.01-1.57), while wind speed also showed statistically significant associations with cases 5-6 days later. CONCLUSIONS: Results suggest that primary MERS human cases in Saudi Arabia are more likely to occur when conditions are relatively cold and dry. This is similar to seasonal patterns that have been described for other respiratory diseases in temperate climates. It was hypothesized that low visibility would be positively associated with primary cases of MERS, however the opposite relationship was seen. This may reflect behavioural changes in different weather conditions. This analysis provides key initial evidence of an environmental component contributing to the development of primary MERS-CoV infections.

Times from Infection to Disease-Induced Death and their Influence on Final Population Sizes After Epidemic Outbreaks.

For epidemic models, it is shown that fatal infectious diseases cannot drive the host population into extinction if the incidence function is upper density-dependent. This finding holds even if a latency period is included and the time from infection to disease-induced death has an arbitrary length distribution. However, if the incidence function is also lower density-dependent, very infectious diseases can lead to a drastic decline of the host population. Further, the final population size after an epidemic outbreak can possibly be substantially affected by the infection-age distribution of the initial infectives if the life expectations of infected individuals are an unbounded function of infection age (time since infection). This is the case for lognormal distributions, which fit data from infection experiments involving tiger salamander larvae and ranavirus better than gamma distributions and Weibull distributions.

Modeling livestock population structure: a geospatial database for Ontario swine farms.

BACKGROUND: Infectious diseases in farmed animals have economic, social, and health consequences. Foreign animal diseases (FAD) of swine are of significant concern. Mathematical and simulation models are often used to simulate FAD outbreaks and best practices for control. However, simulation outcomes are sensitive to the population structure used. Within Canada, access to individual swine farm population data with which to parameterize models is a challenge because of privacy concerns. Our objective was to develop a methodology to model the farmed swine population in Ontario, Canada that could represent the existing population structure and improve the efficacy of simulation models. RESULTS: We developed a swine population model based on the factors such as facilities supporting farm infrastructure, land availability, zoning and local regulations, and natural geographic barriers that could affect swine farming in Ontario. Assigned farm locations were equal to the swine farm density described in the 2011 Canadian Census of Agriculture. Farms were then randomly assigned to farm types proportional to the existing swine herd types. We compared the swine population models with a known database of swine farm locations in Ontario and found that the modeled population was representative of farm locations with a high accuracy (AUC: 0.91, Standard deviation: 0.02) suggesting that our algorithm generated a reasonable approximation of farm locations in Ontario. CONCLUSION: In the absence of a readily accessible dataset providing details of the relative locations of swine farms in Ontario, development of a model livestock population that captures key characteristics of the true population structure while protecting privacy concerns is an important methodological advancement. This methodology will be useful for individuals interested in modeling the spread of pathogens between farms across a landscape and using these models to evaluate disease control strategies.

Do fatal infectious diseases eradicate host species?

In simple SI epidemic and endemic models, three classes of incidence functions are identified for their potential to be associated with host extinction: weakly upper density-dependent incidences are never associated with host extinction. Power incidences that depend on the number of susceptibles and infectives by powers strictly between 0 and 1 are associated with initial-constellation-dependent host extinction for all parameter values. Homogeneous incidences, of which frequency-dependent incidence is a very particular case, and power incidences are associated with global host extinction for certain parameter constellations and with host survival for others. Laboratory infection experiments with salamander larvae are equally well fitted by power incidences and certain upper density-dependent incidences such as the negative binomial incidence and do not rule out homogeneous incidences such as an asymmetric frequency-dependent incidence either.

A longitudinal study describing horse demographics and movements during a competition season in Ontario, Canada.

The objective of this study was to describe the demographics and movement patterns of a sample of horses in Ontario, Canada. A convenience sample of 222 owners completed an initial questionnaire to provide demographic information for 570 horses. These horses were enrolled in a longitudinal study to document their movements from May to November 2015 using a monthly questionnaire. The median age of the participating horses was 11 years (IQR: 8 to 16 years). The primary discipline of participating horses included competitive disciplines (63.3%), leisure (33.3%), and racing (3.2%). During the 7-month period, there were 3001 unidirectional movements of horses between facilities. Reasons for travel on/off a facility included attending a competition (38.7%), leisure activities (18.8%), and training (7.5%). The demographic and movement data presented in this study provide insight into the characteristics of a subset of horses in Ontario, and may contribute to outbreak preparedness in the population.

Étude longitudinale décrivant les données démographiques des chevaux et leurs mouvements durant une saison compétitive en Ontario, au Canada. L'objectif de cette étude consistait à décrire les données démographiques et les mouvements d'un échantillon de chevaux en Ontario, au Canada. Un échantillon utile était composé de 222 propriétaires qui ont rempli un premier questionnaire afin de fournir des données démographiques pour 570 chevaux. Ces chevaux étaient inscrits dans une étude longitudinale afin de documenter leurs mouvements de mai à novembre 2015 à l'aide d'un questionnaire mensuel. L'âge médian des chevaux participants était de 11 ans (IQR : 8 à 16 ans). La discipline primaire des chevaux participants comprenait des disciplines de compétition (63,3 %), d'agrément (33,3 %) et de course (3,2 %). Durant la période de 7 mois, il y a eu 3001 déplacements unidirectionnels de chevaux entre les installations. Les raisons des déplacements à l'aller ou au départ d'une installation incluaient une compétition (38,7 %), des activités d'agrément (18,8 %) et l'entraînement (7,5 %). Les données sur la démographie et les mouvements dans cette étude ont fourni des renseignements sur les caractéristiques d'un sous-groupe de chevaux en Ontario et pourront contribuer à la préparation aux éclosions au sein de la population.(Traduit par Isabelle Vallières).

Understanding the early dynamics of the 2014 porcine epidemic diarrhea virus (PEDV) outbreak in Ontario using the incidence decay and exponential adjustment (IDEA) model.

BACKGROUND: The United States swine industry was first confronted with porcine epidemic diarrhea virus (PEDV) in 2013. In young pigs, the virus is highly pathogenic and the associated morbidity and mortality has a significant negative impact on the swine industry. We have applied the IDEA model to better understand the 2014 PEDV outbreak in Ontario, Canada. Using our simple, 2-parameter IDEA model, we have evaluated the early epidemic dynamics of PEDV on Ontario swine farms. RESULTS: We estimated the best-fit R0 and control parameter (d) for the between farm transmission component of the outbreak by fitting the model to publically available cumulative incidence data. We used maximum likelihood to compare model fit estimates for different combinations of the R0 and d parameters. Using our initial findings from the iterative fitting procedure, we projected the time course of the epidemic using only a subset of the early epidemic data. The IDEA model projections showed excellent agreement with the observed data based on a 7-day generation time estimate. The best-fit estimate for R0 was 1.87 (95% CI: 1.52 - 2.34) and for the control parameter (d) was 0.059 (95% CI: 0.022 - 0.117). Using data from the first three generations of the outbreak, our iterative fitting procedure suggests that R0 and d had stabilized sufficiently to project the time course of the outbreak with reasonable accuracy. CONCLUSIONS: The emergence and spread of PEDV represents an important agricultural emergency. The virus presents a significant ongoing threat to the Canadian swine industry. Developing an understanding of the important epidemiological characteristics and disease transmission dynamics of a novel pathogen such as PEDV is critical for helping to guide the implementation of effective, efficient, and economically feasible disease control and prevention strategies that are able to help decrease the impact of an outbreak.

Descriptive and network analyses of the equine contact network at an equestrian show in Ontario, Canada and implications for disease spread.

BACKGROUND: Identifying the contact structure within a population of horses attending a competition is an important element towards understanding the potential for the spread of equine pathogens as the horses subsequently travel from location to location. However, there is limited information in Ontario, Canada to quantify contact patterns of horses. The objective of this study was to describe the network of potential contacts associated with an equestrian show to determine how this network structure may influence potential disease transmission. RESULTS: This was a descriptive study of horses attending an equestrian show in southern Ontario, Canada on July 6 and 7, 2014. Horse show participants completed a questionnaire about their horse, travel patterns, and infection control practices. Questionnaire responses were received from horse owners of 79.7% (55/69) of the horses attending the show. Owners reported that horses attending the show were vaccinated for diseases such as rabies, equine influenza, and equine herpesvirus. Owners demonstrated high compliance with most infection control practices by reporting reduced opportunities for direct and indirect contact while away from home. The two-mode undirected network consisted of 820 nodes (41 locations and 779 horses). Eight percent of nodes in the network represented horses attending the show, 87% of nodes represented horses not attending the show, but boarded at individual home facilities, and 5% represented locations. The median degree of a horse in the network was 33 (range: 1-105). CONCLUSIONS: Developing disease management strategies without the explicit consideration of horses boarded at individual home facilities would underestimate the connectivity of horses in the population. The results of this study provides information that can be used by equestrian show organizers to configure event management in such a way that can limit the extent of potential disease spread.

Stochastic agent-based modeling of tuberculosis in Canadian Indigenous communities.

BACKGROUND: In Canada, active tuberculosis (TB) disease rates remain disproportionately higher among the Indigenous population, especially among the Inuit in the north. We used mathematical modeling to evaluate how interventions might enhance existing TB control efforts in a region of Nunavut. METHODS: We developed a stochastic, agent-based model of TB transmission that captured the unique household and community structure. Evaluated interventions included: (i) rapid treatment of active cases; (ii) rapid contact tracing; (iii) expanded screening programs for latent TB infection (LTBI); and (iv) reduced household density. The outcomes of interest were incident TB infections and total diagnosed active TB disease over a 10- year time period. RESULTS: Model-projected incidence in the absence of additional interventions was highly variable (range: 33-369 cases) over 10 years. Compared to the 'no additional intervention' scenario, reducing the time between onset of active TB disease and initiation of treatment reduced both the number of new TB infections (47% reduction, relative risk of TB = 0.53) and diagnoses of active TB disease (19% reduction, relative risk of TB = 0.81). Expanding general population screening was also projected to reduce the burden of TB, although these findings were sensitive to assumptions around the relative amount of transmission occurring outside of households. Other potential interventions examined in the model (school-based screening, rapid contact tracing, and reduced household density) were found to have limited effectiveness. CONCLUSIONS: In a region of northern Canada experiencing a significant TB burden, more rapid treatment initiation in active TB cases was the most impactful intervention evaluated. Mathematical modeling can provide guidance for allocation of limited resources in a way that minimizes disease transmission and protects population health.

Modélisation mathématique de la transmission de la COVID-19 et stratégies d'atténuation des risques dans la population ontarienne au Canada.

CONTEXTE: Au Canada, on utilise des interventions d'éloignement physique pour ralentir la propagation du SRAS-CoV-2 (coronavirus du syndrome respiratoire aigu sévère 2), mais on ignore au juste quelle en sera l'efficacité. Nous avons évalué comment différentes interventions non pharmacologiques pouvaient être utilisées pour maîtriser la pandémie de COVID-19 (maladie à coronavirus 2019) et alléger le fardeau qu'elle impose au système de santé. MÉTHODES: Nous avons utilisé un modèle à compartiments structuré selon l'âge pour faire une analyse de la transmission de la COVID-19 dans la population de l'Ontario, au Canada. Nous avons comparé un scénario de référence, soit dépistage limité, isolement et quarantaine, à des scénarios incluant dépistage accru, mesures strictes d'éloignement physique, ou combinaison de dépistage accru et d'éloignement physique moins strict. Les interventions étaient appliquées soit pendant des durées fixes, soit selon un cycle dynamique en fonction de l'occupation projetée des lits dans les unités de soins intensifs (USI). Nous présentons les médianes et les intervalles de crédibilité tirés de 100 expériences répliquées par scénario sur un horizon temporel de 2 ans. RÉSULTATS: Selon le scénario de référence, nous avons estimé que 56 % (intervalle de crédibilité de 95 %, 42 %­63 %) de la population ontarienne contractait l'infection pendant l'épidémie. Au moment du sommet épidémique, nous avons projeté 107 000 (intervalle de crédibilité de 95 %, 60 760­149 000) hospitalisations (soins standards) et 55 500 (intervalle de crédibilité de 95 %, 32 700­75 200) hospitalisations dans les USI. Pour les scénarios à durée fixe, selon les projections, toutes les interventions retardaient et réduisaient la hauteur du sommet épidémique par rapport au scénario de référence, et ce sont les mesures d'éloignement physique strict qui exerçaient le plus d'effet; de même, les interventions de durée plus longue étaient plus efficaces. Selon les projections, les interventions dynamiques réduisaient la proportion de la population atteinte à la fin de la période de 2 ans et pouvaient ramener le nombre médian de cas dans les USI en deçà des estimations actuelles de leur capacité en Ontario. INTERPRÉTATION: Sans éloignement physique substantiel ou une combinaison d'éloignement physique modéré et de dépistage accru, nous projetons que les ressources des USI pourraient être insuffisantes. L'éloignement physique dynamique maintiendrait la capacité du système de santé en plus de donner un répit psychologique et économique périodique aux populations.