Overdiagnosis of Malaria Illness in an Endemic Setting: A Facility-Based Surveillance Study in Malawi

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  • 1 Center for Vaccine Development and Global Health, University of Maryland Baltimore, Baltimore, Maryland;
  • 2 Blantyre Malaria Project, College of Medicine, University of Malawi, Blantyre, Malawi;
  • 3 Malaria Alert Center, College of Medicine, University of Malawi, Blantyre, Malawi;
  • 4 Department of Global Health, Boston University School of Public Health, Boston, Massachusetts;
  • 5 Department of Osteopathic Medical Specialties, College of Osteopathic Medicine, Michigan State University, East Lansing, Michigan

In endemic settings where asymptomatic malaria infections are common, malaria infection can complicate fever diagnosis. Factors influencing fever misdiagnosis, including accuracy of malaria rapid diagnostic tests (mRDTs) and the malaria-attributable fraction of fevers (MAF), require further investigation. We conducted facility-based surveillance in Malawi, from January 2012 through December 2013 in settings of high perennial (Chikhwawa), high seasonal (Thoylo), and moderate seasonal (Ndirande) malaria transmission. Consecutive patients presenting to outpatient departments were screened; those with suspected malaria illness were tested by mRDT or routine thick-smear microscopy. Test positivity rates (TPRs), positive predictive value (PPVs) of mRDTs, and MAFs were calculated by site, age, and season. Of 41,471 patients, 10,052 (24.2%) tested positive for malaria. The TPR was significantly greater in Chikhwawa (29.9%; 95% CI, 28.6–30.0) compared with Thyolo (13.2%; 95% CI, 12.5–13.7) and Ndirande (13.1%; 95% CI, 12.2–14.4). The overall PPV was 77.8% (95% CI, 76.8–78.7); it was lowest among infants (69.9%; 95% CI, 65.5–74.2) and highest among school-age children (81.9%; 95% CI, 80.3–83.4). Malaria infection accounted for about 50% of fevers in children younger than 5 years old with microscopy-confirmed Plasmodium falciparum infection, and less than 20% of such fevers in school-age children. Outpatient settings in Malawi had a high burden of malaria illness, but also possible overdiagnosis of malaria illness. Interventions to reduce malaria transmission and rapid testing for other common febrile illness may improve diagnostic clarity among outpatients in malaria endemic settings.

Author Notes

Address correspondence to Miriam Laufer, 685 W Baltimore St., HSF1, Rm. 480, Baltimore, MD 21201. E-mail: mlaufer@som.umaryland.edu

Financial support: This work was supported by the NIH–National Institute of Allergy and Infectious Diseases (U19AI089683 and K24AI114996). We acknowledge the support of the University of Maryland Baltimore Institute for Clinical and Translational Research.

Authors’ addresses: Ingrid Peterson, Center for Vaccine Development and Global Health, University of Maryland Baltimore, Baltimore, MD, and Blantyre Malaria Project, College of Medicine, University of Malawi, Blantyre, Malawi, E-mail: idpet2@gmail.com. Atupele Kapito-Tembo, Andrew Bauleni, and Don P. Mathanga, Malaria Alert Center, College of Medicine, University of Malawi, Blantyre, Malawi, E-mails: atupelekapito@gmail.com, abauleni@mac.medcol.mw, and dmathang@mac.medcol.mw. Osward Nyirenda and Paul Pensulo, Blantyre Malaria Project, College of Medicine, University of Malawi, Blantyre, Malawi, E-mails: omnyirenda@gmail.com and paulpensulo@gmail.com. William Still, Lauren Cohee, and Miriam Laufer, Center for Vaccine Development and Global Health, University of Maryland Baltimore, Baltimore, MD, E-mails: wstill@umaryland.edu, lcohee@som.umaryland.edu, and mlaufer@som.umaryland.edu. Clarissa Valim, Department of Global Health, Boston University School of Public Health, Boston, MA, E-mail: clariss.valim@gmail.com. Terrie Taylor, Department of Osteopathic Medical Specialties, College of Osteopathic Medicine, Michigan State University, East Lansing, MI, E-mail: ttmalawi@msu.edu.

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