Analysis of the Incidence and Severity of Cellulitis During the COVID-19 Pandemic in Japan

During the COVID-19 pandemic, a decline in various infectious disease cases was observed. However, changes in dermatological infectious diseases, particularly cellulitis, and the potential impact of delayed consultations on severe cases have not been fully explored. To investigate changes in the number of cellulitis patients and severe cases during the COVID-19 pandemic. We employed a difference-in-differences (DID) design using a de-identified claims database from 242 acute-care hospitals across Japan to compare the pre-pandemic period (January 1, 2015, to December 31, 2019) with the pandemic period (January 1, 2020, to December 31, 2020). The national state of emergency, declared by the Japanese government in April 2020 in response to COVID-19, was treated as an exogenous shock. The study analyzed outpatient, inpatient, and total cases, sepsis and bacteremia complications, ambulance transport rates, length of hospital stay, and inpatient comorbidities. A total of 28 673 cellulitis cases were analyzed (24 256 from 2015 to 2019; 4417 in 2020). Severity indicators included hospitalization (8.2%), sepsis (4.1%), bacteremia (1.7%), and ambulance transport (17.0%). In the DID analysis, a significant decrease was observed in total cellulitis cases (incidence rate ratio [IRR]: 0.91; 95% confidence interval [CI]: 0.85-0.97), outpatient cases (IRR: 0.92; 95% CI: 0.86-0.98), and inpatient cases (IRR: 0.81; 95% CI: 0.66-0.99). No significant differences were found in sepsis (IRR: 0.53; 95% CI: 0.26-1.10), bacteremia (IRR: 0.73; 95% CI: 0.19-2.86), ambulance transport (IRR: 0.81; 95% CI: 0.50-1.29), or length of hospital stay (IRR: 0.83; 95% CI: 0.66-1.03). During the pandemic, the number of cellulitis cases treated in Japanese acute-care hospitals decreased without a significant rise in severe cases, suggesting the possibility that avoidance of medical consultations may not have worsened outcomes. Pandemic-related behavioral changes may have contributed to the reduced incidence.