Epidemiological Changes in Acute Febrile Diseases after the COVID-19 Pandemic in Thailand.

Acute undifferentiated febrile illnesses (AUFIs) are short-duration infectious diseases with nonspecific symptoms. In Thailand, common AUFIs include dengue, malaria, leptospirosis, scrub typhus, and typhoid fever. This study aimed to determine the case numbers of AUFI etiologies in Thailand before coronavirus disease 2019 (COVID-19) (phase 1 from January 2018 to February 2020) and during the COVID-19 pandemic with preventive measures (phase 2 from March 2020 to April 2022), and the loosening of the preventive measures (phase 3 from May 2022 to December 2022). We used Thailand's national database from 2018 to 2022 to determine the case numbers of AUFIs and geographic heat maps to identify endemic areas in Thailand. The case numbers of malaria, dengue, leptospirosis, typhoid, and scrub typhus significantly decreased during phase 2 (preventive measures) (P = 0.02), and cases of malaria and leptospirosis increased during phase 3 (loosened preventive measures) (P = 0.01). In 2022, malaria and leptospirosis increased by 39% and 48%, respectively, compared with the previous year. Malaria increased in western Thailand along the border between Thailand and Myanmar, where malaria preventive measures were insufficient, whereas leptospirosis increased in northern Thailand. The epidemiology of acute febrile diseases changes significantly depending on the global epidemic of infectious diseases such as COVID-19 and the implementation of preventive measures, such as face masks, hand hygiene, social distancing, and stay-at-home and lockdown measures.