|Malaria Diagnosis: New Perspectives (WHO - OMS, 2000, 57 p.)|
|5. DIAGNOSTIC PRACTICES|
People with little or no previous exposure to malaria, who therefore often have no immunity, may become rapidly and severely ill upon infection and need prompt diagnosis and therapy. Moreover, travellers and other newly infected persons may find themselves in situations in which reliable health care is not available. In such circumstances RDTs for malaria may have a useful role, as demonstrated in the examples below.
· Complex emergencies, such as those caused by conflicts or environmental catastrophes, create conditions that may facilitate the introduction and spread of malaria. These include: the displacement of non-immune populations into malaria-endemic areas; environmental changes that allow breeding of malaria vectors; concurrent health problems such as malnutrition; and the unavailability, at least initially, of food, sanitation and basic health care to address general health problems, including the diagnosis and treatment of malaria. In many complex emergencies, malaria may cause up to 40-50% of all illness; if a risk exists, an assessment should be made of malarias share as a cause of mortality and morbidity. The assessment should also include the parasite species involved and the efficacy of anti-malarial treatments. This information can be applied to facilitate targeted prevention and treatment strategies. Microscopic diagnosis being rarely possible in acute emergencies, RDTs can at least initially play a crucial role, for example, in monitoring the accuracy of clinical diagnosis, rapidly assessing malaria prevalence or the response to antimalarial drugs.
· Malaria epidemics may occur in complex emergencies, but can also result from environmental changes and population migration (44). Such epidemics constitute an increasing problem, and their early detection and prevention constitutes one of the four basic technical elements of the Global Malaria Control Strategy (1). In epidemic situations where pre-existing health services can provide microscopy, this diagnostic approach should be adopted to support clinical diagnosis. In areas where such services are unavailable, the use of RDTs to confirm the epidemic in its early stages can be especially useful. This was exemplified during a recent malaria epidemic in Kisii and Gucha districts of Kenya, where random sampling with RDTs was used to assess P. falciparum infection rates prior to targeted interventions to control the epidemic (Allan R, personal communication, 1999).
· Malaria in returning travellers is a diagnostic challenge in which RDTs, if used correctly, might prove useful. Over 12 000 annual cases have recently been reported in Europe, where case fatality rates among patients with P. falciparum malaria can reach 3.6% (45). In non-endemic countries, the prompt and accurate detection of malaria in febrile returning travellers is critical. These individuals are often non-immune and a delay in diagnosis can prove fatal. Unfortunately, health personnel in non-endemic countries frequently lack experience in the microscopic diagnosis of malaria, or there can be appreciable delays in obtaining results. Such problems could be alleviated by the use of RDTs. Studies on returning febrile travellers, comparing the results obtained with RDTs to those obtained with expert microscopy or PCR, found that both sensitivity and specificity were in general above 90%. These initial findings are encouraging and indicate that RDTs could be used in a supporting role to identify rapidly P. falciparum infections when prompt microscopic diagnosis is problematic in the home country. Nevertheless, all patients with initially negative RDT results should be monitored, and RDTs should not be considered as a replacement for expert microscopy. Of greatest concern is the fact that, in non-immune individuals, symptomatic malaria can occur at parasite densities that are below the detection threshold of currently available RDTs.
· Stand-by emergency self-treatment in travellers constitutes another application of RDTs that has been proposed by certain groups. In this approach, the traveller is expected to self-diagnose and treat a possible malaria attack when medical attention is not available within 24 hours of the onset of symptoms. RDT kits are marketed in several European countries for self-use by travellers, and some also contain antimalarial drugs for self-treatment. Under such conditions, the utilization of such devices has been shown to be technically problematic. Healthy volunteers at a travel clinic in Switzerland were able to learn how to perform the test. especially if the standard written instructions of the manufacturers were supplemented with verbal information; but their interpretation of prepared tests showing a range of possible test results was unsatisfactory, with an unacceptably high rate of false-negative interpretations (46, 47). In a recent study in febrile European tourists in Kenya, only 68% were able to perform the RDTs correctly, and 10 out of 11 with microscopically confirmed malaria failed to diagnose themselves accurately (48). Thus, major technical modifications are required before such RDT kits can be recommended for use by travellers.
· Military forces (and organized workforces) are sporadically exposed to malaria, but often do not have laboratory staff with adequate experience in malarial microscopy. RDTs could play a valuable supporting role to microscopy in garrisons, and could be the primary diagnostic tool at the front line, for use by medical auxiliaries. For such purposes, it would be important that the test kits be robust and that the packaging contain all the necessary supplies for blood collection and testing.