Low-density asymptomatic parasitemia in southern Zambia does not lead to clinical malaria and is not associated with household transmission: results from a two-year cohort study.

Background: In low malaria transmission settings targeting elimination, the World Health Organization recommends a combination of mass (e.g., mass test-and-treat), targeted (e.g., chemoprophylaxis or treatment for travelers), and reactive (e.g., reactive drug administration) strategies. Most of these strategies would not identify and treat individuals with asymptomatic parasitemia. This study was conducted in a pre-elimination setting in Southern Province, Zambia to examine risk factors for asymptomatic parasitemia, its epidemiologic relationship to incident clinical malaria, and evidence of its contribution to ongoing transmission to inform policy on whether these parasitemic individuals need to be identified and treated to achieve malaria elimination. Methods: An intensive longitudinal cohort study of 197 households within the catchment area of a single health center was designed to capture all clinical malaria cases and episodes of asymptomatic parasitemia between 2018 and 2020. During monthly collections, all household members and overnight visitors were administered a questionnaire and a blood sample was collected to identify Results: Of the 1071 individuals enrolled in the cohort, 144 (13%) were positive by qPCR for Conclusion: Low-level parasitemia was prevalent despite few cases of clinical malaria in this low transmission setting. There was no evidence that low-level asymptomatic parasitemia led to clinical cases of malaria or transmission to other household members.