Recently, it has been reported that respiratory viruses are often detected in bacterial pneumonia patients; however, there are no reports on aspiration pneumonia. The purpose of the study was to investigate the frequency and clinical background of respiratory virus infection in aspiration pneumonia.

Patients with a clinical diagnosis of lower respiratory tract infection from emergency department visits at Chubu Hospital, Okinawa, Japan, between February 2020 and January 2021 were retrospectively included. The residual swab specimens at the time of their visits were used to perform polymerase chain reaction test to investigate respiratory virus infections.

Respiratory viral infections were observed in 28 of 59 patients with aspiration pneumonia, 59 of 118 patients with non-aspiration pneumonia, and 17 of 32 patients with acute bronchitis, with rhinovirus being the most frequently detected virus species in all groups. SARS-CoV-2 was also included in 2, 5, and 3 cases, respectively. Compared to its non-aspiration pneumonia, aspiration pneumonia had a higher proportion of pure viral infections and a lower positive sputum culture rate. It also had a lower rate of infiltrate on chest X-ray. The prevalence of neurological disease or psychiatric disease and welfare-facility utilization were over 80% as background for aspiration pneumonia. In each group, there was no apparent difference in clinical findings based on the presence or absence of respiratory virus infection.

In conclusion, a significant number of respiratory virus infections were included in clinically diagnosed aspiration pneumonia patients. Differentiating respiratory virus infection from aspiration pneumonia was difficult.