Articles

<i><b>Background:</b></i> COVID-19-related pneumonia was initially rare, though influenza-related pneumonia is well known as a severe complication of influenza. However, COVID-19-related pneumonia may be increasing since the omicron variant of COVID-19 appeared. <i><b>Methods:</b></i> The clinical differences between COVID-19-related and influenza-related pneumonia patients were retrospectively investigated in patients hospitalized from January 2022 to December 2023. <i><b>Results:</b></i><i><b> </b></i>COVID-19-related and influenza-related pneumonias were found in 46 of 285 (15.8%) and 6 of 12 (50.0%) patients, respectively (p<0.001). Their mean ages were 75.5 (45-93) years and 53.8 (19-73) years in COVID-19-related and influenza-related pneumonia cases, respectively (p=0.002). Aspiration pneumonia was more common in COVID-19-related pneumonia (28/46=60.9%) than in influenza-related pneumonia patients, and it was treated by sulbactam/ampicillin (31/46=67.4%). The influenza-related pneumonia patients were more often infected in the work place (2/6=33.3%) and not vaccinated (4/6=66.7%), compared with COVID-19-related patients. Death occurred in 7 of 46 (15.2%) COVID-19 patients, but none of 6 influenza-infected patients died. <i><b>Conclusions:</b></i> These data suggest that COVID-19-related pneumonia presented as aspiration pneumonia in older patients, although influenza-related pneumonia was more common in younger and non-vaccinated patients and might be associated with immune mechanisms during the omicron variant surge era.

The initial omicron (B.1.1.529) severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) subvariants, BA.1 and BA.2 (BA.1/2), were progressively displaced by BA.5 in Japan, which showed not only higher transmittivity and less pathogenicity, but also differences in antibiotic use according to the difference in the clinical course of BA.5 compared with BA.1/2 infections. BA.5 patients received more antibiotics, especially ampicillin/sulbactam, although ceftriaxone and meropenem were used significantly in the BA.1/2 period. These data suggest an increased incidence of aspiration pneumonia in elderly patients in the BA.5 period, and we should consider changing the management tactics for COVID-19.