Hospital-acquired (or ‘nosocomial’) SARS-CoV-2 infection continues to pose significant harm to patients, despite a decrease in morbidity and mortality rates observed since the pre-Omicron period, as per the recent research findings published in the Annals of Internal Medicine. This retrospective study, conducted from December 2020 to April 2023, involved a cohort of hospitalized adults across five acute care hospitals in Massachusetts.
The researchers captured data from two distinct periods: the pre-Omicron (December 1, 2020-December 14, 2021) and the Omicron period (December 15, 2021-April 30, 2023). The study used the Hospital Day 5 and onwards SARS-CoV-2 positive diagnostic data of patients who had previously tested negative at admission and on Hospital Day 3. These patients were then matched using detailed criteria with controls (patients without infection) in a 1:2 ratio.
Primary outcomes assessed included overall hospital mortality and the median time from patient matching to discharge. Various statistical methods including Poisson, quantile and weighted Cox regression models were applied. The analysis ultimately included 230 patients with hospital-onset infections and their 460 counterparts in the pre-Omicron period, as well as 865 patients with such infections and their 1730 counterparts during the Omicron period.
Notably, in both observed periods, there was a significant statistical rise in in-hospital mortality rates and an extended median time to hospital discharge among patients with nosocomial SARS-CoV-2 compared to their non-infected counterparts. The risk of Intensive Care Unit (ICU) admission and the requirement for high-flow oxygen were also significantly increased among the infected during the pre-Omicron period.
Interestingly, while the risk for ICU admission remained elevated among patients during the Omicron period, the need for high-flow oxygen seemed to lessen, and the requirement for mechanical ventilation increased. The persistence of the association between hospital-onset SARS-CoV-2 infection and the extended hospital stay was highlighted in the subgroup analysis.
However, the study recognized limitations including its potentially low generalizability as it was restricted to Massachusetts. Misclassification bias and residual confounding were other possible limitations. Despite these, the overarching conclusion suggested that the increased frequency and persistent morbidity implicated with hospital-onset SARS-CoV-2 infections during the Omicron era necessitate the implementation of stricter measures for the prevention of nosocomial infections, especially in elevated community SARS-CoV-2 rates scenario, by healthcare institutions.