Impact of 2018 Japan Floods on Asthma Prescriptions: A Longitudinal Analysis

Background The impact of flood disasters on adult asthma is poorly understood. Objective To investigate the impact of the 2018 Japan Floods on new prescriptions of asthma controller medications and treatments for asthma exacerbations in adults. Methods This retrospective longitudinal analysis utilised data from the National Database of Health Insurance Claims for residents of regions severely affected by the 2018 Japan Floods, covering 1 year before and 1 year after the disaster. New asthma controller prescriptions were compared between officially certified disaster victims and non-victims without controller use in the preceding year. Among prior controller users, prescriptions for short-acting β 2 -agonists and oral corticosteroids were compared between groups. Results Among 5,000,129 participants, 31,235 were disaster victims. Victims had a higher incidence of new asthma controller prescriptions than non-victims (adjusted hazard ratio, 1.47; 95% confidence interval, 1.38–1.57). The increase was observed across all age groups and was greater in younger and middle-aged adults. Difference-in-differences analysis showed increased short-acting β 2 -agonist prescriptions at 3, 5, 7, and 11 months and increased oral corticosteroid prescriptions at 5 months among victims. Conclusion Victims of the 2018 Japan Floods had increased prescriptions for new-onset and exacerbated asthma, suggesting an association between flood disasters and increased adult asthma-related healthcare needs.