Among patients admitted to the emergency department (ED), outcomes are more severe in those infected with the SAR-CoV-2 Omicron variant than in those infected with influenza or respiratory syncytial virus (RSV). These findings were published in Clinical Infectious Diseases.

This retrospective multicenter study was designed to compare outcomes of COVID-19 Omicron variant infection against those of seasonal influenza and RSV among patients admitted to the ED. Researchers sourced data for this analysis from patient who were tested for all 3 viruses at 1 of 6 acute care hospitals in Sweden between 2021 and 2022. The primary outcome was 30-day all-cause mortality; secondary outcomes included 90-day all-cause mortality, hospitalization, and intensive care unit (ICU) admission. Patients infected with Omicron also were compared against a prepandemic cohort of patients who were infected with influenza (n=5709) or RSV (n=995) between 2015 and 2019.

Among patients in the COVID-19 Omicron (n=4833), influenza (n=1099), and RSV (n=453) cohorts, the median ages were 70.0, 56.0, and 72.0 years; 50.9%, 43.1%, and 45.7% were men; and 9.5%, 10.7%, and 12.4% had obesity, respectively. The most common comorbidities among the entire study population were hypertension and cardiac or cerebrovascular disease.

The rate of 30-day all-cause mortality was 7.9% among patients with Omicron infection, 2.5% among those with influenza, and 6.0% among those with RSV. In the adjusted analysis, the risk of 30-day all-cause mortality was significantly higher among patients with Omicron infection when compared against those with influenza (adjusted odds ratio [aOR], 2.36; 95% CI, 1.60-3.62) and those with RSV (aOR, 1.42; 95% CI, 0.94-2.21).

Omicron infections were both more common and were associated with more severe outcomes compared with seasonal influenza and RSV infections, particularly among unvaccinated individuals.

In a subgroup of patients who were not vaccinated against COVID-19 infection, the 30-day all-cause mortality rate associated with Omicron infection increased to 8.4%. Moreover, the higher risk of 30-day mortality associated with Omicron infection was more pronounced in unvaccinated patients vs those with influenza (aOR, 5.51; 95% CI, 3.41-9.18) and those with RSV (aOR, 3.29; 95% CI, 2.01-5.56).

Further analysis showed that both 90-day all-cause mortality (aOR, 2.31; 95% CI, 1.65-3.30) ICU admission (aOR, 2.49; 95% CI, 1.34-4.63) were more likely with Omicron infection vs influenza. However, hospitalization was less likely with Omicron infection vs influenza (aOR, 0.90; 95% CI, 0.81-1.00). For patients infected with Omicron vs RSV, 90-day all-cause mortality was more likely (aOR, 1.27; 95% CI, 0.88-1.88), hospitalization was less likely (aOR, 0.68; 95% CI, 0.60-0.78), and the risk for ICU admission was similar (aOR, 1.04; 95% CI, 0.54.200).

Among unvaccinated patients, 90-day all-cause mortality risk was increased among those infected with Omicron vs influenza (aOR, 4.94; 95% CI, 3.17-7.88) or RSV (aOR, 2.72; 95% CI, 1.75-4.31). Unvaccinated patients infected with Omicron vs influenza also were more likely to require hospitalization (aOR, 1.30; 95% CI, 1.14-1.49) and ICU admission (aOR, 4.96; 95% CI, 2.56-9.60). However, in unvaccinated patients infected with Omicron vs those with RSV, ICU admission was more likely (aOR, 2.82; 95% CI, 1.39-5.73) but hospitalization risk was similar (aOR, 0.92; 95% CI, 0.79-1.08).

In the prepandemic cohort, the risk for 30-day all-cause mortality was significantly higher among patients infected with Omicron vs both influenza (aOR, 2.17; 95% CI, 1.80-2.62) and RSV (aOR, 1.49; 95% CI, 1.12-2.01).

Limitations of this study include the lack of data on influenza vaccination status and the possible influence of different treatment strategies on patient outcomes.

According to the researchers, “Omicron infections were both more common and were associated with more severe outcomes compared with seasonal influenza and RSV infections, particularly among unvaccinated individuals.”

This article originally appeared on Infectious Disease Advisor

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