Clinical and epidemiological features of healthcare workers after a coronavirus disease 2019 cluster infection in Japan and the effects of Kampo formulas-Hochuekkito and Kakkonto: A retrospective cohort study.

It is expected that a low-toxicity natural compound like Kampo formulas would exhibit a preventive effect on COVID-19, in a global outbreak of coronavirus disease 2019 (COVID-19). Although the biological properties and safety of the representative Kampo, Hochuekkito (HET), and Kakkonto (KKT) have been confirmed in various animal model experiments and clinical studies, and in a few human studies to induce biological effects on various infectious diseases without significant toxicity, it is unclear whether HET and KKT are safe and effective for COVID-19 prevention. We summarized the clinical characteristics of HCWs and the preventive effects of HET and KKT. We performed a retrospective, single-center, cohort study that included 175 HCWs (aged 21-77 years) from a total number of 217 in a hospital with a history of COVID-19 cluster infection. In total, 175 HCWs were tested for severe acute respiratory coronavirus virus 2 (SARS-CoV-2) antibodies. We identified 27 patients (median age: 49 ± 10.7 years) who were diagnosed with COVID-19. The patients in the group that had a body mass index ≥ 25 had a high COVID-19 infection risk, while those in the group with a Kampo formula adherence rate ≥ 40% had a low COVID-19 risk. Patients in the group with an adherence rate ≥ 40%, as well as those in the current alcohol consumption group, were at a low risk of developing severe COVID-19. In conclusion, HET and KKT may have prevented the onset or worsening of COVID-19, which could be clinically used. Obesity might have increased the patients' susceptibility to COVID-19 and the disease severity.