Public health investigation of COVID-19 cases hospitalized during the fifth wave in Montreal, Canada

Respiratory Diseases

During the fifth wave of the COVID-19 pandemic in Montreal, caused by the Omicron variant, the weekly incidence of COVID-19 cases and hospitalizations reached its highest. The objective of this study was to rapidly characterize hospitalizations and identify risk factors to prioritize interventions, including access to limited doses of Paxlovid™.
A matched case-control study using telephone interviews and hospital chart reviews was conducted. A sample of persons with PCR-confirmed COVID-19, hospitalized in Montreal, tested between December 20, 2021 and January 23, 2022 (identified from Quebec administrative hospitalizations database [Med-Echo]) were matched (1:1 ratio) to non-hospitalized persons with PCR-confirmed COVID-19, based on neighbourhood of residence, age group and sampling date. Descriptive analyses and multivariate conditional logistic regression analyses were performed.
The study included 390 matched pairs (n=780). Median duration of hospitalizations involving a COVID-19 admission (AD) and/or primary diagnosis (PD) (58%) was 10 days, compared to 5 days for persons hospitalized for other reasons with a concurrent COVID-19 diagnosis (36%). Immune system diseases (OR: 11.69 [1.35-101]), kidney diseases (OR: 11.05 [1.49-82.12]), shortness of breath (OR: 4.94 [2.04-11.93]) and loss of appetite (OR: 3.37 [1.12-10.10]) were risk factors for COVID-19 hospitalization. Heart problems, diabetes, and chronic neurological disorders were associated with a higher risk of shortness of breath. Among all factors associated with hospitalization, vaccination with two or three doses had the strongest, negative, association (OR: 0.02 [0.00-0.24]).
The difference in hospitalization duration highlights the importance of distinguishing hospitalizations with a COVID-19 AD or PD from hospitalizations with a concurrent COVID-19 diagnosis. Risk factors for hospitalization were consistent with provincial indications for Paxlovid™ treatment and with risk factors reported in the literature for previous variants. Vaccination remains a priority public health intervention as it was highly effective in preventing hospitalization during the COVID-19 fifth wave in Montreal.

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