Low quality of routine microscopy for malaria at different levels of the health system in Dar es Salaam.

Judith Kahama-Maro,Christian Lengeler,Blaise Genton,Deo Mtasiwa,Valerie D'Acremont

doi:10.1186/1475-2875-10-332

Abstract

BackgroundLaboratory capacity to confirm malaria cases in Tanzania is low and presumptive treatment of malaria is being practiced widely. In malaria endemic areas WHO now recommends systematic laboratory testing when suspecting malaria. Currently, the use of Rapid Diagnostic Tests (RDTs) is recommended for the diagnosis of malaria in lower level peripheral facilities, but not in health centres and hospitals. In this study, the following parameters were evaluated: (1) the quality of routine microscopy, and (2) the effects of RDT implementation on the positivity rate of malaria test results at three levels of the health system in Dar es Salaam, Tanzania.MethodsDuring a baseline cross-sectional survey, routine blood slides were randomly picked from 12 urban public health facilities in Dar es Salaam, Tanzania. Sensitivity and specificity of routine slides were assessed against expert microscopy. In March 2007, following training of health workers, RDTs were introduced in nine public health facilities (three hospitals, three health centres and three dispensaries) in a near-to-programmatic way, while three control health facilities continued using microscopy. The monthly malaria positivity rates (PR) recorded in health statistics registers were collected before (routine microscopy) and after (routine RDTs) the intervention in all facilities.ResultsAt baseline, 53% of blood slides were reported as positive by the routine laboratories, whereas only 2% were positive by expert microscopy. Sensitivity of routine microscopy was 71.4% and specificity was 47.3%. Positive and negative predictive values were 2.8% and 98.7%, respectively. Median parasitaemia was only three parasites per 200 white blood cells (WBC) by routine microscopy compared to 1226 parasites per 200 WBC by expert microscopy. Before RDT implementation, the mean test positivity rates using routine microscopy were 43% in hospitals, 62% in health centres and 58% in dispensaries. After RDT implementation, mean positivity rates using routine RDTs were 6%, 7% and 8%, respectively. The sensitivity and specificity of RDTs using expert microscopy as reference were 97.0% and 96.8%. The positivity rate of routine microscopy remained the same in the three control facilities: 71% before versus 72% after. Two cross-sectional health facility surveys confirmed that the parasite rate in febrile patients was low in Dar es Salaam during both the rainy season (13.6%) and the dry season (3.3%).ConclusionsThe quality of routine microscopy was poor in all health facilities, regardless of their level. Over-diagnosis was massive, with many false positive results reported as very low parasitaemia (1 to 5 parasites per 200 WBC). RDTs should replace microscopy as first-line diagnostic tool for malaria in all settings, especially in hospitals where the potential for saving lives is greatest.

Highlights

Laboratory capacity to confirm malaria cases in Tanzania is low and presumptive treatment of malaria is being practiced widely
Of these 346 slides, results of expert microscopy were missing for two slides and the routine results for nine slides could not be obtained because the patients did not return to the clinicians to complete the consultation process
Of the remaining 335 slides, 178 (53.1%) slides were reported positive by health facility routine microscopy but only 7 (2.1%) were positive by expert microscopy

Summary

Introduction

Laboratory capacity to confirm malaria cases in Tanzania is low and presumptive treatment of malaria is being practiced widely. The use of Rapid Diagnostic Tests (RDTs) is recommended for the diagnosis of malaria in lower level peripheral facilities, but not in health centres and hospitals. In Tanzania, malaria was until recently the leading cause of attendance in health facilities, with an estimated 16 million cases annually and 70,000 deaths [2]. Of all the malaria cases reported annually only 12-20% are confirmed parasitologically [3] This is a common finding in the majority of African countries where the proportion of cases that have a confirmed diagnosis is usually less than 20% [1]. It has been common practice to base diagnosis of malaria mainly on clinical signs and symptoms in health facilities across Africa due to the scarcity of laboratory facilities [5,6]. A recent survey conducted in Tanzania to assess health services provision in health facilities revealed that laboratory capacity to diagnose malaria was available in only 33% of health facilities, mostly in hospitals, and less in government than private health facilities [7]

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