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Background  Rapid diagnostic tests (RDTs) detecting histidine-rich protein 2 ( Pf HRP2) antigen are used to identify individuals with  Plasmodium falciparum  infection even in low transmission settings seeking to achieve elimination. However, these RDTs lack sensitivity to detect low-density infections, produce false negatives for  P. falciparum  strains lacking  pfhrp2  gene and do not detect species other than  P. falciparum .    Methods  Results of a  Pf HRP2-based RDT and  Plasmodium  nested PCR were compared in a region of declining malaria transmission in southern Zambia using samples from community-based, cross-sectional surveys from 2008 to 2012. Participants were tested with a  Pf HRP2-based RDT and a finger prick blood sample was spotted onto filter paper for PCR analysis and used to prepare blood smears for microscopy. Species-specific, real-time, quantitative PCR (q-PCR) was performed on samples that tested positive either by microscopy, RDT or nested PCR.    Results  Of 3,292 total participants enrolled, 12 (0.4%) tested positive by microscopy and 42 (1.3%) by RDT. Of 3,213 (98%) samples tested by nested PCR, 57 (1.8%) were positive, resulting in 87 participants positive by at least one of the three tests. Of these, 61 tested positive for  P. falciparum  by q-PCR with copy numbers ≤ 2 x 10 3  copies/μL, 5 were positive for both  P. falciparum  and  Plasmodium malariae  and 2 were positive for  P. malariae  alone. RDT detected 32 (53%) of  P. falciparum  positives, failing to detect three of the dual infections with  P. malariae . Among 2,975 participants enrolled during a low transmission period between 2009 and 2012, sensitivity of the  Pf HRP2-based RDT compared to nested PCR was only 17%, with specificity of >99%. The  pfhrp  gene was detected in 80% of  P. falciparum  positives; however, comparison of copy number between RDT negative and RDT positive samples suggested that RDT negatives resulted from low parasitaemia and not  pfhrp2  gene deletion.    Conclusions  Low-density  P. falciparum  infections not identified by currently used  Pf HRP2-based RDTs and the inability to detect non- falciparum  malaria will hinder progress to further reduce malaria in low transmission settings of Zambia. More sensitive and specific diagnostic tests will likely be necessary to identify parasite reservoirs and achieve malaria elimination.    Electronic supplementary material  The online version of this article (doi:10.1186/s12936-015-0544-3) contains supplementary material, which is available to authorized users.

malaria journal

Comparison of a PfHRP2-based rapid diagnostic test and PCR for malaria in a low prevalence setting in rural southern Zambia: implications for elimination