Abstract
BackgroundThe use of malaria rapid diagnostic tests (RDTs) has been widely advocated to improve Plasmodium falciparum diagnosis, especially in settings where quality microscopy is not available. RDTs based on the detection of histidine-rich protein 2 (HRP-2) can remain positive for several weeks after an infection is cured, due to the persistence of HRP-2 antigens. As a result, test specificity may vary between age groups with different prevalence of P. falciparum infection.MethodsA community-based cross-sectional survey, carried out in southern Tanzania in July and August 2004, evaluated the performance of the Paracheck Pf in comparison with microscopy (number of P. falciparum parasites/200 leucocytes). A sample of 598 individuals living in an area of intense malaria transmission had demographic data collected before an RDT was performed. HRP-2 test sensitivity, specificity, positive and negative predictive values were calculated and compared between distinct age groups, using microscopy as "gold standard".ResultsThe overall malaria prevalence was 34.3% according to microscopy and 57.2% according to the HRP-2 test. The HRP-2 test had a sensitivity of 96.1%, a specificity of 63.1%, a positive predictive value of 57.6% and a negative predictive value of 96.9%. The test sensitivity was higher (ranging from 98% to 100%) amongst people less than 25 years of age, but decreased to 81.3% in older adults. The HRP-2 test specificity varied between age groups, ranging from 25% among children of five to nine years of age, to 73% among adults aged 25 or more. The test positive predictive value increased with malaria prevalence, while the negative predictive value was consistently high across age groups.ConclusionsThese results suggest that the performance of HRP-2 tests in areas of intense malaria transmission varies by age and the prevalence of P. falciparum infection. The particularly low specificity among children will lead to the over-estimation of malaria infection prevalence in this group.
Highlights
The use of malaria rapid diagnostic tests (RDTs) has been widely advocated to improve Plasmodium falciparum diagnosis, especially in settings where quality microscopy is not available
Baseline characteristics of the sample and P. falciparum infection prevalence Sampled individuals were distributed across two divisions (Litehu and Namikupa) of Tandahimba District
34.3% [95% CI 26.5-42.0%] of the study sample was infected with P. falciparum and no significant differences were found between genders or across divisions (Table 3)
Summary
The use of malaria rapid diagnostic tests (RDTs) has been widely advocated to improve Plasmodium falciparum diagnosis, especially in settings where quality microscopy is not available. Rapid diagnostic tests (RDTs) for malaria were developed in the early 1990’s, and welcomed with great enthusiasm as a tool to improve malaria diagnosis, especially in remote areas of Africa where access to microscopy is often limited due to the lack of resources and skilled technicians. In such settings, malaria diagnosis frequently relies on clinical criteria, which have a low specificity, by asexual forms and young gametocytes of P. falciparum. Many studies have demonstrated that the sensitivity of HRP-2 based tests declines sharply when the parasite density falls below 100 to 500 parasites/μL [6,8,9,13,14,15]
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