Epidemiologic trends and clinical outcomes of imported malaria in a tertiary care hospital, Bangkok, Thailand: A retrospective analysis (2013-2022).

Background: Despite a significant declined in malaria incidence in Thailand, the rising global travel has resulted in an increase of imported malaria cases, posing a threat to the goal of malaria elimination. This study aims to understand the epidemiological trends and clinical outcomes of imported malaria cases in Thailand.

Methods: Medical records of all imported malaria cases admitted from 1 January 2013 to 31 December 2022 at the Hospital for Tropical Diseases, Thailand, were retrospectively examined. Demographic data, travel details, severity of illness, and clinical outcomes were described. Logistic regression was performed to identify factors associated with severe disease outcomes.

Results: In total, 335 cases of imported malaria were identified, with 33 % classified as transnational malaria and 67 % as border malaria. Transnational malaria cases (79 % P. falciparum) were mostly acquired from Sub-Saharan Africa for business or visiting friends and relatives (VFRs). Border malaria cases (81 % P. vivax) involved unskilled labourers and were acquired from land-border countries. The proportion of imported malaria in business travelers increased from 13 % to 50 % over the ten years. Risk factors for severe imported malaria included male gender, age 40 and older, infection with P. falciparum, and acquired malaria from Africa.

Conclusions: Understanding unique demographic and socioeconomic characteristics in both border and transnational cases is crucial for effective malaria prevention. The increasing imported malaria among business travelers highlight the need for targeted prevention in this high-risk group.