April 18, 2026
2 min read
Key takeaways:
- Influenza may contribute more to winter deaths than records indicate, a study found.
- Researchers said the findings demonstrate a need for enhanced surveillance.
MUNICH — Winter deaths associated with influenza may be significantly undercounted, a team of Spanish researchers found.
The researchers conducted an observational study of 857 patients who died during four influenza seasons in Spain. Among them, 11% tested positive for influenza after death, but only 17% of those cases had been diagnosed while they were alive, and influenza was named as the cause of death in just 1.4% of cases.
Data derived from Argente L, et al. Abstract O0014. Presented at: ESCMID Global; April 17-21, 2026; Munich.
These gaps, according to the researchers, suggest that influenza may contribute more to winter mortality than records show.
“The results of this pilot study were very surprising,” Jesús Castilla, MD, PhD, of the Public Health Institute of Navarra in Pamplona, Spain, told Healio. “The impact of respiratory viral infections on mortality may be higher than previously thought.”
In their study, Castilla and colleagues obtained postmortem swabs within 24 hours of death and conducted PCR testing for a broad panel of respiratory viruses. The study included four influenza seasons spanning 2016-2017 through 2019-2020 in the Navarre region of Spain. Influenza was not the only undercounted respiratory illness. According to the researchers, rhinovirus, human coronavirus and respiratory syncytial virus infections were also missed while patients were alive.
Castilla said the findings likely reflect an undercounting of influenza deaths in other parts of the world.
“The number of deaths with a confirmed diagnosis of influenza and other respiratory virus infection is very low as compared with such excess mortality. Therefore, it seems that the results may be valid for other countries and regions,” he said.
The researchers noted that, among older people and those with underlying conditions, influenza symptoms are often less pronounced or masked by existing illness, potentially causing the undercounting of influenza deaths.
To expand on this research, Castilla said he and his team have launched a similar study but with a larger cohort.
“We’ve continued this study and have increased the number of deceased people recruited,” he said, while adding that such a study is “challenging” because it requires collaboration of a laboratory, a funeral company and a team of epidemiologists.
For more information:
Jesús Castilla, MD, PhD, can be reached at jcastilc@navarra.es.
Perspective
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Amesh A. Adalja, MD
Disclosures: Adalja reports no relevant financial disclosures.
Sources/Disclosures
Source:
Argente L, et al. Abstract O0014. Presented at: ESCMID Global; April 17-21, 2026; Munich.
References:
Disclosures:
The authors report no relevant financial disclosures.
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