Journal Article

Impact of COVID-19 pandemic on Legionella testing and infection rates in Ontario

Zhang, Pauline, Sullivan, Ashleigh, Li, Ye, Murphy, Allana, Leibson, Keren, Bi, Yingli, Gubbay, Jonathan B., Peci, Adriana, Majury, Anna

2025

Overview

Background The disruption of healthcare systems during the COVID-19 pandemic had widespread effects on patient care, including interruption of scheduled visits and diagnostic testing. Many diseases were under-investigated due to the focus on the SARS-CoV-2 virus and the redeployment of resources to the pandemic response. This study aimed to assess Legionella trends in Ontario during the COVID-19 pandemic years, by comparing the demographics of individuals tested for Legionella prior to pandemic (2018 and 2019) to those during the pandemic (2020, 2021 and 2022). Additionally, for individuals who underwent Legionella testing, testing for additional respiratory pathogens was examined in the context of Legionella co-detection. Methods Two Poisson regression models were constructed to compare testing rate and positivity rate during the pre-pandemic years with the pandemic years, adjusted for age, sex, year, and Ontario population. Results Relative to the pre-pandemic years, the testing rates significantly decreased by 8% in 2020, decreased by 8% in 2021 and increased by 14% in 2022. The positivity rate for Legionella decreased by 13% only in 2020 but did not reach significance for the other two years. Individuals older than 50 years of age and males remained the population with highest positivity rate of Legionella infection across all years. Co-detection of Legionella with SARS-CoV-2 or seasonal respiratory viruses was rare but present during the pandemic. Conclusions Legionella  testing rates decreased by 8% in 2020 and 8% in 2021 and increased by 14% in 2022, which was associated with a decrease in positivity rate only in 2020, at 13%, but not in the other two years. Maintaining vigilance for Legionella  testing in future pandemics may support timely diagnosis and treatment, leading to improved patient outcomes. Co-detection of Legionella with SARS-CoV-2 or seasonal respiratory viruses was rare but present during the pandemic. Accordingly, Legionella testing remains essential among high-risk groups, such as the elderly with co-morbidities, critically ill patients, or those with severe or unresponsive pneumonia. Such an approach can aid in differential diagnosis, prompt appropriate treatment, and improve patient outcomes.

• Publisher: BioMed Central,BioMed Central Ltd,Springer Nature B.V,BMC
• Subject: Adolescent / Adult / Age / Aged / Biostatistics / Care and treatment / Child / Child, Preschool / Co-infection / Control / COVID-19 / COVID-19 - epidemiology / COVID-19 pandemic / Demographics / Diagnosis / Differential diagnosis / Disease / Environmental Health / Epidemics / Epidemiology / Female / Health services / Humans / Influenza / Investigations / Laboratories / Legionella / Legionella - isolation & purification / Legionella positivity rates / Legionella testing / Legionellosis / Legionellosis - diagnosis / Legionellosis - epidemiology / Legionnaires' disease / Male / Medicine / Medicine & Public Health / Middle Aged / Ontario / Ontario - epidemiology / Pandemics / Pathogens / Patients / Pneumonia / Population / Public Health / Regression analysis / Regression models / Respiratory diseases / Respiratory syncytial virus / Respiratory viruses / Risk factors / Risk groups / SARS-CoV-2 / Severe acute respiratory syndrome coronavirus 2 / Surveillance / Vaccine / Vigilance / Viral diseases / Viruses / Young Adult