Respiratory Viral Infections Research / Pneumonia and Respiratory Infections · Journal article

Trends in Respiratory Virus Positivity Across Urban and Rural Hospitals in Ontario over Three Seasons

Ijid Regions · September 1, 2026

Preliminary Why this matters to you Expert discussion

Early or partial results. Treat as a signal, not a conclusion.

AI Summary

This is a descriptive surveillance report documenting positivity rates and temporal shifts in 15 respiratory viruses across Ontario hospitals over three seasons (2022–2025). The data document that adenovirus and SARS-CoV-2 peaked earlier in 2024–2025 compared to prior years, while influenza A and RSV peaked later in 2024–2025, suggesting changes in transmission dynamics that warrant ongoing monitoring.

What was studied

Multicentre retrospective surveillance analysis. Patients tested for respiratory viruses at Ontario hospitals during three consecutive respiratory virus seasons; urban and rural hospitals included.. Ontario, Canada.

Key findings

Influenza A, RSV, and SARS-CoV-2 reached the highest positivity rates at 11.6%, 13%, and 11.7%, respectively. Adenovirus and SARS-CoV-2 peaked much earlier in 2024–2025 compared to previous years. Influenza A virus peaked later in 2024–2025 compared to 2023–2024.

Safety

Safety was not reported in the material analysed. Check the source before drawing any conclusion about harm.

Who this may help

Clinicians and public health professionals should note documented shifts in seasonal timing of major respiratory viruses in Ontario, particularly earlier peaks for adenovirus and SARS-CoV-2 in 2024–2025. This information may inform timing of diagnostic testing, infection control measures, and public health messaging, pending confirmation through prospective surveillance.

Plain-language summary

Retrospective surveillance analysis describing seasonal patterns and temporal shifts in respiratory virus positivity across Ontario hospitals, without a comparator group or formal hypothesis testing, representing descriptive epidemiology.

Study design

As stated by the source record.

MethodsMolecular testing data for 15 respiratory viruses were collected over three consecutive respiratory virus seasons. Hospital-level variability was assessed by calculating deviations from each hospital's peak week from the seasonal median peak week, summarized across years for each virus. The timing of the weekly peak in test positivity for each virus was analysed.

DesignMulticentre retrospective surveillance analysis

PopulationPatients tested for respiratory viruses at Ontario hospitals during three consecutive respiratory virus seasons; urban and rural hospitals included.

SettingOntario, Canada

Reported figures

Quoted from the source exactly as published.

Influenza A positivity rate11.6%

RSV positivity rate13%

SARS-CoV-2 positivity rate11.7%

Clinical bottom line

Caveats

Total sample size, number of hospitals, and denominator for positivity calculation not reported.
No comparison with pre-pandemic seasons; causality of timing shifts not established.
Hospital-level variability described qualitatively; quantitative measures of deviation not reported.
Urban versus rural differences mentioned in title but not analysed or reported in text.

Evidence assessment

Graded across the dimensions that decide whether you should act, each from what the source actually supports. There is no single score, and where a dimension was not assessed it says so.

Study design

moderate

Multicentre retrospective analysis of molecular testing data across three seasons.

Directness

moderate

Reports positivity rates and peak timing; does not assess clinical outcomes or interventions.

Consistency

limited

Describes shifts in peak timing; does not compare consistency across hospitals or report variability metrics.

Risk of bias

limited

Retrospective design; hospital-level selection and testing practices not reported.

Sample adequacy

insufficient

Total sample size, number of hospitals, and denominator for positivity rates not stated.

Source abstract

Background Respiratory viruses are a global health burden. While influenza has been a large focus of surveillance, non-influenza viruses remain understudied in Canada, leaving gaps in understanding their seasonal patterns and epidemiology. The COVID-19 pandemic further disrupted typical virus seasonality, highlighting the urgent need for expanded surveillance to track evolving trends. Methods A multicentre retrospective analysis of molecular testing data for 15 respiratory viruses was conducted on tests performed over three consecutive respiratory virus seasons. Hospital-level variability was assessed by calculating deviations from each hospital’s peak week from the seasonal median peak week, summarized across years for each virus. We analysed the timing of the weekly peak in test positivity for each virus. Results Each respiratory virus showed distinct yearly peak weeks, with influenza A, RSV, and SARS-CoV-2 reaching the highest positivity rates (11.6%, 13%, and 11.7%, respectively). Significant shifts in peak timing were observed for adenovirus, SARS-CoV-2, influenza A virus, parainfluenza virus, and RSV across the 2022-2025 seasons, with adenovirus and SARS-CoV-2 peaking much earlier in 2024-2025, compared to previous years. Influenza A virus peaked later and RSV also peaked later only in the 2024-2025 season compared to 2023-2024. Conclusions Overall, our results highlight shifts in respiratory virus transmission dynamics across Ontario hospitals. Ongoing surveillance will support targeted public health interventions and strategies for respiratory virus surges.

Follow from this

Taken from the source record, never inferred. Follow any of these and new work involving them reaches your briefing.

Andrew MendlowitzChristie VermeirenRobert W. KozakKevin C. KatzMia J. BiondiR. DengRespiratory Viral Infections ResearchPneumonia and Respiratory Infections