High Levels of Asymptomatic and Subpatent Plasmodium falciparum Parasite Carriage at Health Facilities in an Area of Heterogeneous Malaria Transmission Intensity in the Kenyan Highlands

Gillian H. Stresman Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Kenya Medical Research Institute, Centre for Global Health Research, Centers for Disease Control and Prevention/Kenya Medical Research Institute, Kisumu, Kenya; Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland; Department of Medical Microbiology, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Radboud University, Nijmegen Medical Centre, Nijmegen, The Netherlands

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Jennifer C. Stevenson Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Kenya Medical Research Institute, Centre for Global Health Research, Centers for Disease Control and Prevention/Kenya Medical Research Institute, Kisumu, Kenya; Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland; Department of Medical Microbiology, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Radboud University, Nijmegen Medical Centre, Nijmegen, The Netherlands

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Nnenna Ngwu Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Kenya Medical Research Institute, Centre for Global Health Research, Centers for Disease Control and Prevention/Kenya Medical Research Institute, Kisumu, Kenya; Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland; Department of Medical Microbiology, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Radboud University, Nijmegen Medical Centre, Nijmegen, The Netherlands

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Elizabeth Marube Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Kenya Medical Research Institute, Centre for Global Health Research, Centers for Disease Control and Prevention/Kenya Medical Research Institute, Kisumu, Kenya; Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland; Department of Medical Microbiology, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Radboud University, Nijmegen Medical Centre, Nijmegen, The Netherlands

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Chrispin Owaga Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Kenya Medical Research Institute, Centre for Global Health Research, Centers for Disease Control and Prevention/Kenya Medical Research Institute, Kisumu, Kenya; Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland; Department of Medical Microbiology, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Radboud University, Nijmegen Medical Centre, Nijmegen, The Netherlands

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Chris Drakeley Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Kenya Medical Research Institute, Centre for Global Health Research, Centers for Disease Control and Prevention/Kenya Medical Research Institute, Kisumu, Kenya; Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland; Department of Medical Microbiology, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Radboud University, Nijmegen Medical Centre, Nijmegen, The Netherlands

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Teun Bousema Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Kenya Medical Research Institute, Centre for Global Health Research, Centers for Disease Control and Prevention/Kenya Medical Research Institute, Kisumu, Kenya; Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland; Department of Medical Microbiology, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Radboud University, Nijmegen Medical Centre, Nijmegen, The Netherlands

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Jonathan Cox Department of Immunology and Infection, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Department of Disease Control, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Kenya Medical Research Institute, Centre for Global Health Research, Centers for Disease Control and Prevention/Kenya Medical Research Institute, Kisumu, Kenya; Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland; Department of Medical Microbiology, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, United Kingdom; Radboud University, Nijmegen Medical Centre, Nijmegen, The Netherlands

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In endemic settings, health facility surveys provide a convenient approach to estimating malaria transmission intensity. Typically, testing for malaria at facilities is performed on symptomatic attendees, but asymptomatic infections comprise a considerable proportion of the parasite reservoir. We sampled individuals attending five health facilities in the western Kenyan highlands. Malaria prevalence by rapid diagnostic test (RDT) was 8.6–32.9% in the health facilities. Of all polymerase chain reaction-positive participants, 46.4% (95% confidence interval [95% CI] = 42.6–50.2%) of participants had infections that were RDT-negative and asymptomatic, and 55.9% of those infections consisted of multiple parasite clones as assessed by merozoite surface protein-2 genotyping. Subpatent infections were more common in individuals reporting the use of non-artemisinin–based antimalarials in the 2 weeks preceding the survey (odds ratio = 2.49, 95% CI = 1.04–5.92) compared with individuals not reporting previous use of antimalarials. We observed a large and genetically complex pool of subpatent parasitemia in the Kenya highlands that must be considered in malaria interventions.

Author Notes

* Address correspondence to Gillian H. Stresman, Department of Immunology and Infection, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom. E-mail: Gillian.Stresman@lshtm.ac.uk

Financial support: This research was funded by the Bill and Melinda Gates Foundation as part of Malaria Transmission Consortium Grant 45114. C.D. is supported by Wellcome Trust Grant 091924. T.B. is supported by Grand Challenge Grant OPP1024438 from the Bill and Melinda Gates Foundation.

Authors' addresses: Gillian H. Stresman and Chris Drakeley, Department of Immunology and Infection, London School of Hygiene and Tropical Medicine, London, United Kingdom, E-mails: Gillian.Stresman@lshtm.ac.uk and Chris.Drakeley@lshtm.ac.uk. Jennifer C. Stevenson, Johns Hopkins Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, E-mail: jennyc.stevenson@macharesearch.org. Nnenna Ngwu, St. Georges Healthcare National Health Service (NHS) Trust, London, United Kingdom, E-mail: nsongwu@gmail.com. Elizabeth Marube, Kenya Medical Research Institute, Centre for Global Health Research, Kisumu, Kenya, E-mail: Emarube@kemricdc.org. Chrispin Owaga, Safe Water and AIDS Project, Kisumu, Kenya, E-mail: cowage@gmail.com. Teun Bousema, Department of Immunology and Infection, London School of Hygiene and Tropical Medicine, London, United Kingdom, and Radboud University, Nijmegen Medical Centre, Nijmegen, The Netherlands, E-mail: Teun.Bousema@lshtm.ac.uk. Jonathan Cox, Department of Disease Control, London School of Hygiene and Tropical Medicine, London, United Kingdom, E-mail: Jonathan.Cox@lshtm.ac.uk.

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