Prevalence of PCR Detectable Malaria Infection among Febrile Patients with a Negative Plasmodium falciparum Specific Rapid Diagnostic Test in Zanzibar

Abstract

Abstract. We screened for malaria in 594 blood samples from febrile patients who tested negative by a Plasmodium falciparum-specific histidine-rich protein-2-based rapid diagnostic test at 12 health facilities in Zanzibar districts North A and Micheweni, from May to August 2010. Screening was with microscopy, polymerase chain reaction (PCR) targeting the cytochrome b gene (cytbPCR) of the four major human malaria species, and quantitative PCR (qPCR). The prevalence of cytbPCR-detectable malaria infection was 2% (12 of 594), including 8 P. falciparum, 3 Plasmodium malariae, and 1 Plasmodium vivax infections. Microscopy identified 4 of 8 P. falciparum infections. Parasite density as estimated by microscopy or qPCR was 4,000 parasites/μL in 5 of 8 cytbPCR-detectable P. falciparum infections. The infections that were missed by the rapid diagnostic test represent a particular challenge in malaria elimination settings and highlight the need for more sensitive point-of-care diagnostic tools to improve case detection of all human malaria species in febrile patients.Zanzibar has been the site of a substantial recent effort to reduce the overall burden of malaria. With these efforts, the prevalence of parasitologically confirmed malaria infection among febrile children presenting at primary health care facilities in Zanzibar has decreased from~25% in 2003 1 to 2% in 2010 (Shakely and others, unpublished data). Historically, Plasmodium falciparum has played a dominant role in malarial illness in Zanzibar, and elsewhere in sub-Saharan Africa, causing well over 90% of episodes of the disease 2,3 ; the remaining reported malaria infections in Zanzibar in recent years have been caused by Plasmodium malariae. 2Malaria rapid diagnostic tests (RDTs) that detect parasite antigens have improved the availability of parasite-based diagnosis for rural clinics in Africa. 4 However, the RDT currently used in most of sub-Saharan Africa and in Zanzibar at the time of this study detects histidine-rich protein-2 (HRP2), which is specific to P. falciparum, and does not detect other species of malaria parasites. 5The availability of highly sensitive molecular techniques provides an opportunity to better characterize the species of Plasmodia causing malaria in regions of sub-Saharan Africa experiencing decreasing P. falciparum transmission. The aim of this study was to assess the prevalence of polymerase chain reaction (PCR)-detectable malaria infection among febrile patients with a negative P. falciparum-specific RDT in Zanzibar.Samples for this study were from an RDT effectiveness trial (Shakely and others, unpublished data) performed in 12 Zanzibar primary health care facilities, six each in North A and Micheweni districts over a 12-week period during the high transmission season from May to August 2010. Inclusion criteria in this study were: age 2 months, a measured axillary temperature 37.5 C or history of fever in the preceding 24 hours, and absence of any danger signs of severe disease. 6After obtaining informed written consent, dried b...

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