Study: Hospital-based COVID-19 less serious after Omicron

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Hospital-acquired (nosocomial) COVID-19 transmission was associated with higher rates of 30-day mortality and more severe disease during the early phases of the pandemic, but the risk has lessened in the post-Omicron landscape, according to a new study from JAMA Network Open based on outcomes seen in Sweden during the past 3 years.

Outcomes of nosocomial SARS-CoV-2 infections are important metrics for hospital prevention and control measures, including masking, ventilation, and mandatory testing of patients. The authors of the study said up-to-date assessments of hospital-acquired COVID-19 infections is needed for the planning and implementation of infection prevention and control (IPC) measures.

In an editorial on the study, clinicians from Harvard University and Brigham and Women's Hospital in Boston said, "Hospital leaders face the dilemma of deciding whether hospitals and clinics can also revert to prepandemic practices or whether health care ought to be different."

The study looked at the incidence rate of nosocomial SARS-CoV-2 infections across all hospitals in Stockholm, Sweden, from March 1, 2020, to September 15, 2022, and the associated 30-day mortality rates, matching cases with non–COVID-19 hospitalized patients and outcomes.

The proportion of community-acquired, indeterminate, and nosocomial SARS-CoV-2 infections along with the incidence rate of nosocomial SARS-CoV-2 was estimated using data on all SARS-CoV-2 infections, the authors said.

A total of 438,640 SARS-CoV-2 infections were identified during the study period, of which 2,203 nosocomial SARS-CoV-2 infections among 2,193 patients were identified (a few patients were infected more than once). The overall incidence rate of nosocomial SARS-CoV-2 was 1.57 (95% confidence interval [CI], 1.51 to 1.64) per 1,000 patient-days.

The median age for nosocomial patients was 80 years, and 50.5% were women.

Death rate 3 times higher before vaccines

The 30-day mortality rate dropped significantly across the study period, from 34% for nosocomial admitted cases in the prevaccination period (95% CI, 31% to 38%) to 10% (95% CI, 8% to 12%), in the post-Omicron phase.

The excess 30-day mortality was almost 3 times higher in the COVID-19 group compared with the non–COVID-19 group in the prevaccination period, resulting in a roughly 20% absolute increased risk of death in patients who acquired nosocomial COVID-19, the authors said.

"During the Omicron variant wave, after an extensive vaccination campaign, nosocomial infections were not independently associated with excess mortality, suggesting that the role of IPC [infection prevention and control] measures may help prevent excess deaths with successful vaccination and/or less severe virus variants," the authors concluded.

 Nosocomial infections were not independently associated with excess mortality.

In the editorial, the authors write that the study findings suggest nosocomial transmission and mortality after the Omicron period seems to be no longer statistically significant.

"It is very difficult to imagine hospitals reverting to the full array of infection prevention measures they put in place at the height of the pandemic," they write. "We have reached a point at which we can be selective about both the measures we choose and when we implement them. Masking, admission testing, and visitor screening are likely the highest yield interventions."

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