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ANNEX 5. Malaria diagnosis

ANNEX 5
malaria diaGnosis

a5.1 symptom-based (clinical) diagnosis

Malaria is a common cause of fever and illness in endemic areas (1,2); but it is not possible
to accurately diagnose malaria using any one set of clinical criteria, as the signs and
symptoms of malaria, e.g. fever, chills, headache and anorexia, are nonspecific and are
common to many diseases and conditions. The appropriateness of particular clinical
diagnostic criteria varies from area to area according to the intensity of transmission,
the species of malaria parasite and other prevailing causes of fever (3). Other diseases
co-incident with malaria may also affect its presentation. HIV/AIDS can increase the
risk of acquiring malaria or the progression to severe malaria, depending on malaria
transmission in the area and the age of the patient; but it can also lead to an increase in
the incidence of febrile disease that is not malaria, further complicating symptom-based A5
diagnosis of malaria (4).
The use of detailed weighting and scoring systems for clinical signs and symptoms of
malaria may improve the accuracy of clinical diagnosis, but still result in low sensitivity
and specificity. Studies in the Gambia achieved a sensitivity of 70–88% and a specificity
of 63–82%. These methods may also be too complicated to implement and supervise
under operational conditions, and many of the key symptoms and signs of malaria in one
area may not be applicable elsewhere (5,6). A review of 10 studies indicated that the use of
the more restrictive criteria of clinical algorithms resulted in only trivial savings in drug
costs compared with the use of a fever-based diagnosis and, in areas of high prevalence,
it greatly increases the probability of missing malaria infections (7).

a5.2 light microscopy

In addition to providing a diagnosis with a high degree of sensitivity and specificity when
performed well, microscopy allows quantification of malaria parasites and identification
of the infecting species. Light microscopy involves relatively high costs in training and
supervision but, in particular, when the case-load is high, operational costs are low.
Microscopy technicians may also be involved in diagnosis of non-malarial diseases.
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