Study Explores Secondary Bacterial Pneumonia Following Viral Infections

By Dirk Hoffman

Published May 31 in the journal Clinical Infectious Diseases, the paper is titled “Secondary Pneumococcal Disease in Veterans With Viral Respiratory Infections.”

The researchers conducted a retrospective analysis of 188,721 hospitalized patients in Veterans Affairs (VA) hospitals across the United States from 2015 to 2025.

“We know that people often get bacterial pneumonia — especially from a bacterium called Streptococcus pneumoniae — after having viral infections like the flu or RSV,” Hu says. “Our research wanted to find out if COVID-19 also increases the risk of this kind of pneumonia.”

The retrospective study design leveraged the VA’s internal Corporate Data Warehouse — a comprehensive national database that includes health records from VA hospitals across the country.

“This resource allows us to analyze large-scale patient data and explore complex clinical questions, including more nuanced patterns that might not be visible in smaller datasets,” Hu explains.

The researchers compared how often people developed bacterial pneumonia after having the flu, RSV, or COVID-19, helping them to see if COVID-19 leads to similar or different risks compared to these other respiratory viruses.

“We found that people who had the flu or RSV were more likely to develop a secondary bacterial infection caused by Streptococcus pneumoniae. However, this was not the case for people who had COVID-19,” Hu says.

“This may suggest that COVID-19 behaves differently from the flu and RSV when it comes to how it interacts with respiratory bacterial pathogens, and perhaps our immune system.”

Hu says the study offered important insights into how different viral infections affect the risk of secondary bacterial pneumonia.

“Since COVID-19 does not appear to increase this risk the way influenza and RSV do, health care providers may be able to reduce the use of empiric antibiotics in COVID-19 cases,” he says. “This supports more thoughtful treatment decisions as part of antibiotic stewardship — a critical strategy in our fight against antibiotic resistance.”

More broadly, the findings reinforce that COVID-19 is not just another respiratory virus, Hu says.

“It behaves differently and should be considered in its own category,” he adds. “A better understanding of these differences can improve how we diagnose and manage respiratory infections and help shape public health strategies.”

Kari A. Mergenhagen, PharmD, of the Department of Pharmacy in the Veterans Affairs Western New York Healthcare System, is co-senior author on the paper. She is also an adjunct assistant professor of pharmacy practice in UB’s School of Pharmacy and Pharmaceutical Sciences.

“As an infectious disease physician, I work closely with my pharmacy colleagues, both in clinical care and research,” Hu says. “Antibiotic stewardship is a key part of infectious disease management, and it requires a strong, multidisciplinary approach.”

“This study is a great example of that collaboration in action,” he adds. “Our combined expertise can lead to meaningful insights that improve patient care.”

Other co-authors on the study are from the Department of Pharmacy at the VA, and from the D’Youville University School of Pharmacy.