Background Community infections of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have increased rapidly since the emergence of the Omicron strain. During the eighth and ninth pandemic waves—when movement restrictions in the community were eased—the all-case registration system was changed, and the actual status of infection became uncertain. Methods We conducted regular rapid antigen tests (R-RAT) once or twice a week to examine the actual state of coronavirus disease (COVID-19) diagnosis among healthcare employees. Results Overall, 320 (1.42/day) and 299 (1.76/day) employees were infected in the eighth and ninth pandemic waves. During both periods, 59/263 doctors (22.4%), 335/806 nurses (41.6%), 92/194 administrative employees (47.4%), and 129/218 clinical laboratory technicians (59.2%) were infected. In the eighth wave, 56 of 195 employees were infected through close contact; in the ninth wave, 26 of 62 employees were infected. No significant difference was observed in the number of vaccinations between infected and non-infected employees. The positivity rate of R-RAT was 0.41% and 0.45% in the eighth and ninth waves. R-RAT detected infection in 212 and 229 employees during the eighth and ninth waves, respectively; the ratio of R-RAT-detected positive employees to those who reported infection was significantly higher during the ninth wave (odds ratio: 1.67, 95% confidence interval: 1.17–2.37, p

In Kawasaki disease (KD), convulsions are rare and mostly attributed to latent and coexisting encephalitis/encephalopathy due to KD itself. Therefore, we retrospectively investigated concomitant viral infections in patients with KD. Between January 2012 and December 2020, among 523 patients with KD, 7 (1.53%), 1 (0.19%), 6 and 1 (1.15% and 0.19%) were positive for adenovirus (AdV-Ag), respiratory syncytial virus (RSV-Ag), and influenza A or B (Flu A-Ag or Flu B-Ag) antigens, respectively. Among them, two were positive for both AdV-Ag and FluA-Ag. Seven patients with KD (1.3%) presented febrile convulsions, and only one was diagnosed with encephalitis/encephalopathy. Between January 2021 and August 2022, 57 patients with KD were newly diagnosed among whom FilmArray® respiratory panel (FARP) was applied on 24 patients, and 14 (58.3%) were positive for at least one virus. During the same period, 32 out of 45 patients (71.1%) with febrile convulsions examined using the FARP were positive for at least one virus. The trend of viruses in patients with KD and febrile convulsion reflected the regional epidemic viral infection. Respiratory virus detected at a much higher rate using the FARP suggests that most convulsions in patients with KD might be related to concomitant viral infection. The possible involvement and association of concomitant respiratory viral infections in patients with KD with prognosis or encephalopathy/encephalitis remain to be investigated.