Prevalence of influenza and other respiratory viral infections in deceased persons: a population-based observational study over four influenza seasons.

OBJECTIVE

Excess mortality during periods of respiratory virus circulation is very high compared with the number of reported deaths because of these infections. We aimed to estimate the prevalence of infection by influenza and other respiratory viruses in deceased persons during four influenza seasons.

METHODS

Deceased persons, regardless the cause, were swabbed postmortem and tested by PCR for respiratory viruses in the 2016/2017 to 2019/2020 seasons in Navarre, Spain. Postmortem results were compared with the diagnoses from clinical PCR testing.

RESULTS

Of 857 deceased persons with a valid test result, 312 (36.4%) were positive for respiratory viruses: 98 rhinovirus (11.4%), 94 influenza (11.0%), 61 human coronavirus (7.1%), 59 respiratory syncytial virus (6.9%), 14 parainfluenza (1.6%), eight adenovirus (0.9%), six metapneumovirus (0.7%), four bocavirus (0.5%), one enterovirus (0.1%), and one SARS-CoV-2 (0.1%). The prevalence of any respiratory virus remained high throughout the seasons (78/263, 29.7% to 27/57, 47.4%). Among people who tested positive for influenza postmortem, only 41.5% (39/94) had been hospitalized and 17.0% (16/94) had a positive test result for influenza within 30 days before death. The prevalence of influenza postmortem (94/857, 11.0%) contrasted with the prevalence of premortem diagnosis of influenza (23/857, 2.7%) and only 1.4% (12/857) of deaths recorded with influenza as the cause of death.

CONCLUSIONS

Respiratory viral infections were frequently detected in winter deaths, but most of them were not laboratory confirmed before death. The impact of influenza infection on mortality could be higher than the number of persons who are reported as dying from influenza or who die with a confirmed diagnosis of this infection.