Rapid Tests Evaluated Where Malaria Over-Diagnosed

Microscopy is the most common form of malaria diagnosis, but concerns over its accuracy have prompted the incorporation of rapid diagnostic tests (RDTs) into many national malaria control programs.

The malaria RDTs, which require minimal training, have begun to be used for routine malaria testing in a number of African countries and have proved to have high sensitivity and specificity and some can differentiate between malaria species.

Scientists from Princeton University (NJ, USA) working with colleagues in southern Tanzania, directly compared microscopy and RDTs for the diagnosis of malaria over a three months period. Plasmodium falciparum is the only malaria species reported in this region. Between June to mid-August 2011, 400 patients participated in this study and were tested with both microscopy and RDTs.

The ICT Malaria Combo Cassette RDTs (ICT Diagnostics; Cape Town, South Africa) and blood slide microscopy were directly compared. ICT Malaria Combo Cassette Test is a rapid, in vitro diagnostic test for the detection of circulating P. falciparum histidine-rich protein 2 antigen (HRP-2). This antigen that is common to all five species of human malaria is an aldolase antigen.

The apparent prevalence of malaria was 78% based on microscopy whereas the true prevalence, calculated using RDTs as the gold standard, was estimated at 14% in a private dispensary. This discrepancy indicates that when using microscopy as the sole diagnostic test, malaria is being over-diagnosed by approximately a factor of five in this setting. At a public clinic, apparent malaria prevalence based on microscopy was 74%. If similar rates of over-diagnosis are assumed, 5,285 patients of the 6,769 patients positively diagnosed with malaria using microscopy were likely given unnecessary antimalarials, and their true cause of illness was not addressed. The introduction of RDTs to the public clinic would be highly cost-efficient, with an estimated net saving of over USD 96 per month.

The authors concluded that comparing RDTs with microscopy led to almost four out of five patients being over-diagnosed with malaria in this rural part of Tanzania. With estimated prevalence at 14%, RDT introduction is recommended given World Health Organization (Geneva, Switzerland) findings that RDTs are predicted to be cost-effective in prevalence areas of less than 20%. The use of RDTs in malaria diagnosis would not only reduce government spending but would prove beneficial to ensuring appropriate care and treatment of febrile illness. The study was published on May 10, 2013, in the Malaria Journal.

Related Links:
Princeton University
ICT Diagnostics
World Health Organization