Epidemiology of indigenous Plasmodium knowlesi infection in Sarawak, 2011–2019

Objectives To characterise the state‐wide epidemiology of indigenous knowlesi malaria in Sarawak from 2011 to 2019. Methods Longitudinal retrospective study was conducted based on Sarawak knowlesi malaria surveillance data recorded from 2011–2019. Only indigenous cases were included and information extracted for analysis comprised age, sex, occupation, ethnicity, case severity, hospital admission and parasite density. Results Over the 9 years, 8473 indigenous knowlesi malaria cases were recorded. Age group 40–49 years, males, plantation workers and Iban communities recorded the highest percentage of cases in each demographic variable. Most of the cases were uncomplicated (n = 7292; 86.1%) and 89.6% (n = 7589) of the total cases were reported with ≤20 000 parasites/μl of blood. Age group and ethnic group are associated with the severity of knowlesi malaria in Sarawak. Multivariable logistic regression indicated that the age group 60+ years had the highest odds of developing severe knowlesi malaria compared with other age groups (AOR 2.48; 95% CI 1.22, 5.02; p = 0.012). Bidayuh patients were more likely to develop severe knowlesi malaria than Ibans, the largest ethnic group among knowlesi malaria patients (AOR 1.97; 95% CI 1.31, 2.97; p = 0.001). Conclusions Identification of risk groups is important for the implementation of prevention programs and treatments targeting at specific group to combat knowlesi malaria effectively.