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OBJECTIVES:Malaria cross-sectional surveys are rarely conducted in very low transmission settings. This study aimed to determine the prevalence and risk factors of Plasmodium infection in a near-elimination setting in southern Thailand. METHODS:Two cross-sectional surveys were conducted in areas of active transmission in the Surat Thani province of Thailand in January and May 2019. PCR was used to detect Plasmodium infection. RESULTS:The prevalence of Plasmodium blood infection was 0.45% and 0.61% in January and May 2019, respectively. The major parasite species was Plasmodium falciparum in January and Plasmodium vivax in May. Unexpectedly, Plasmodium knowlesi infections were also detected. Most infections, including those of Plasmodium knowlesi, were asymptomatic. Being male and staying outdoors at night-time were the only significant identified risk factors. Of people infected in January 28.0% were positive in May for the same parasite species, suggesting persistent asymptomatic infections. CONCLUSIONS:Despite the very low incidence rate in Surat Thani, most malaria infections were asymptomatic. Outdoor mosquito biting at night-time is likely an important mode of malaria transmission. Unexpectedly, asymptomatic Plasmodium knowlesi infection was found, confirming previous reports of such infection in mainland Southeast Asia.

Original publication




Journal article


International journal of infectious diseases : IJID : official publication of the International Society for Infectious Diseases

Publication Date





445 - 451


Department of Clinical Tropical Medicine, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.


Humans, Plasmodium falciparum, Plasmodium knowlesi, Plasmodium vivax, Malaria, Prevalence, Risk Factors, Cross-Sectional Studies, Polymerase Chain Reaction, Adolescent, Adult, Child, Child, Preschool, Infant, Thailand, Female, Male, Young Adult, Asymptomatic Infections, Surveys and Questionnaires