In response to increasing levels of resistance to conventional monotherapies, such as chloroquine, amodiaquine and sulphadoxine-pyrimethamine, most countries in sub-Saharan Africa have introduced artemisinin-based combination therapy (ACT) for the treatment of uncomplicated malaria [1]. The change in drug policy, combined with aggressive vector control, coincides with a decrease in malaria transmission and subsequent decline in the proportion of fevers attributable to malaria [2]. Although the targeting of anti-malarials only to patients who need them has always been important, changes in drug policy and malaria epidemiology have increased the need for laboratory-based diagnosis of malaria as a means to prevent the emergence of ACT resistance and improve overall clinical management of febrile patients [3,4].

The World Health Organization (WHO) now recommends malaria case management based on parasite-based diagnosis in all cases [5]. Given the difficulty with implementing microscopy-based definitive diagnosis of malaria, malaria rapid diagnostic tests (RDTs) have been suggested as an alternative [6,7]. In line with WHO recommendations, the Malawi National Malaria Control Programme (NMCP) has developed new malaria treatment algorithms, which incorporate the use of RDTs for definitive diagnosis of malaria in patients aged ≥5 years who seek care in health facilities where malaria microscopy is not available.

In preparation for nationwide implementation of RDTs, the NMCP reviewed the commercially available RDTs regarding their target antigen, sensitivity, specificity, shelf-life, heat stability, cost and reliability of suppliers to choose an RDT for national use. Although data is available to inform this selection, much of it comes from field evaluations of a single product at a time with few studies providing head-to-head comparisons of more than one product under operational settings [8-13]. Since factors may vary across regions and countries, the Malawi NMCP requested locally-generated data to aid with the selection of an RDT for national use. Thus, four commercially available RDTs that were being considered as potential candidates for nationwide implementation were evaluated. The study objectives were to assess field sensitivity and specificity, identify factors that might affect RDT field performance, assess prescriber adherence to RDT test results, and explore operational issues regarding RDT implementation.

A total of 2,679 patients were recruited, but only 2,573 (96%) patients with complete RDT and expert microscopy results were included in the analysis. Demographic characteristics varied significantly between persons tested with the different RDTs (Table 1). Malaria prevalence varied significantly at the different RDT testing sites (p < 0.001); the prevalence of microscopically confirmed malaria increased from urban to semi-urban and to rural settings: 3%, 16% and 39% respectively. Overall reported self-treatment with anti-malarials was 12%, but this varied significantly among the different RDT testing sites with a range of 5% in Lilangwe and 29% in Chileka (p < 0.001).

Decreasing malaria transmission leading to a decline in the proportion of fevers attributable to malaria in sub-Saharan Africa and the use of relatively expensive first-line anti-malarials have increased the importance of accurate malaria diagnosis at all levels of the health system [2]. Malaria RDTs must have both high (> 95%) sensitivity and specificity in field settings. High sensitivity is necessary to ensure that true cases of malaria are detected and appropriately managed while high specificity is needed to avoid false positive results that would lead not only to unnecessary anti-malarial treatment but also a missed diagnosis of the true cause of non-malarial fever.

The sensitivity of the RDTs evaluated in this study are similar to the results of other published studies [8-12]. Surprisingly, all of the RDTs evaluated had relatively low specificity resulting in high false positive rates compared to most published studies [8-13]. Only a few studies have reported low specificity [19,20]. Both biological and operational factors that could have resulted in low specificity in this study were explored. HRP2 is known to persist in the blood stream for several weeks and some loss of specificity might be due to patients with circulating antigens, but not live parasites that would be detected by microscopy [20]. In this study, 12% of patients had self-treated with anti-malarials prior to presenting for care to the health facility and might have cleared their parasitaemia, but have residual circulating antigens. The analysis shows that even after adjusting for other factors, self-treatment was significantly associated with lower specificity.

However, even after adjusting for self-treatment with anti-malarials in the past two weeks, two other factors that do not have a plausible biological explanation were independently associated with low specificity: being a patient 5-15 years of age and having the test performed by a community health worker. It is unclear why specificity was lower in patients 5-15 years of age. However, it is possible that health workers interpreting RDTs were more likely to err on the side of caution and interpret questionable test results as positive resulting in reduced specificity. In particular, the specificity was significantly lower when the RDT was performed by a community health worker compared to a laboratory technician. This demonstrates that despite their relative ease of use, the accuracy of RDT results is affected by the cadre of the person performing them. This finding has important implications for training and decisions about which cadre of staff are selected for performing the tests. Access to malaria diagnosis in rural areas is essential for promoting rational clinical care and community health workers have been shown to reliably perform RDTs in other settings [21]. However it is vital that health workers base their clinical decisions on accurate diagnostic test results. Training, certification and supervision of community health workers on RDT use, should therefore be rigorous enough to ensure the reliability and validity RDT test results in field settings. In addition, the specificity is also relatively low (54%) for routine microscopy at the health facilities in this study. The low specificity of both RDTs and microscopy is concerning because it can potentially misguide clinicians, compromise the cost effectiveness of RDTs, and might contribute to the emergence of drug resistance [22-25]. More research needs to be done to further explore this phenomenon, especially in light of upcoming plans to implement RDTs in health facilities in Malawi. This evaluation highlights critical areas for operational research, including who should perform RDTs and how to monitor RDT performance in health facilities.

Over-diagnosis of malaria, involving provision of anti-malarial drugs to patients without evidence of parasitaemia is well documented, and this study documents the magnitude of this problem in Blantyre, Malawi [26-30]. In Malawi, for a considerable period of time, all fevers have been assumed to be malaria. Health education messages have stressed the importance of treating malaria and few diagnostic facilities have been available to support other diagnoses. It is unsurprising, therefore, that over half of all negative test results in this study were disregarded. Nonetheless, this observation serves to highlight that roll out of RDTs should be accompanied by comprehensive package for health workers. This should include not only in-service training emphasizing the need to target malaria treatment to patients with laboratory-confirmed parasitaemia, but also provide alternative treatment for patients with negative malaria diagnostics tests results who have another cause for their febrile illness. Improvement of overall management of febrile patients in remote areas will have to promote use of diagnostic tools for both malaria and other febrile illnesses [31]. Although difficult to interpret since most health workers in routine practice will not have access to both microscopy and RDT results, health workers rarely treated patients with anti-malarials when both microscopy and RDT were negative. Further research into why health workers disregard malaria diagnostic test results is needed given the substantial resources that will be put into RDT scale-up.

Different cadres of health care workers (clinical officers, medical assistants, nurses, community health workers) were involved in the study for both patient recruitment and treatment. The staff mix in the study sites was not uniform. In general health workers in facilities with microscopy were higher ranking than those in remote facilities without microscopy. Abilities to competently manage febrile patients in the sites were, therefore, inherently different. This may have affected degree of adherence to study procedures, RDT manufacturer's instructions, the quality of information collected and ultimately the performance of the RDT tests. In particular, a key limitation of the study was the confounding of RDT type and the health worker cadre who was performing the test (community health worker versus laboratory technician). Although, it was attempted to assess the importance of these two factors on RDT performance by using different multivariable models, it was not possible to fully assess the effects of the test versus the test operator in a single unified model.

Although this was a pilot study used to help guide policy development in Malawi regarding the choice of RDT, other factors such as heat stability, lot-to-lot variation, and ease of use, which would influence the eventual choice of RDT for national policy were not tested. Neither was an evaluation of other practical considerations for country programmes, such as the relative cost of different RDTs and manufacturing capacity of suppliers carried out. Although over 2,500 patients were assessed, the results of this study are meant to be supplementary to other more detailed evaluations, such as the World Health Organization report entitled "Malaria Rapid Diagnostic Test Performance Results of WHO product testing of malaria RDTs: Round 2 (2009)" [6,7].

This evaluation was designed to provide local data for decision making by the Malawi National Malaria Control Programme regarding the scale-up of RDTs in Malawi. The results of this evaluation, combined with other published data and the World Health Organization product testing of malaria RDTs, have been used to help select RDTs for national scale-up [6]. This pilot exercise has highlighted some key issues that need further exploration as Malawi proceeds with RDT scale-up. The low specificity of both RDTs and routine microscopy needs to be further delineated. In addition, operational research on strategies to monitor RDT performance and develop a robust quality assurance system is needed. Lastly, the question of variable RDT performance by different cadres of health workers has to be addressed. Malawi is embarking on rapid scale-up of RDTs in health facilities with the goal of universal diagnosis of all persons more than five years of age. Close monitoring will be needed to ensure that RDTs truly improve malaria case management.

The authors declare that they have no competing interests.

JC participated in the design of the study, supervised data collection, participated in data analysis and drafted the manuscript. JS performed the statistical analysis and reviewed drafted manuscript. BM participated in study design and supervised laboratory work. CC participated in study design. VE supervised data collection and supported drafting of manuscript. MS supported drafting of both analysis plan and the manuscript. JS and DA participated in health worker training, supervised data collection and reviewed manuscript. DM designed the study and supported drafting of manuscript. All authors read and approved the final manuscript.