All episodes of acute illness, in children aged 0-9 years, were registered during 3 years in a health clinic in a village of about 500 inhabitants in a malaria holoendemic area on the Tanzanian coast. Of 668 clinical episodes, 395 were diagnosed as malaria. There was no death. Only 5% of the children with malaria episodes came to the clinic after more than 3 d of symptoms. All 11 severe anaemias occurred among these children. Fever was reported in 98%, vomiting in 15%, and diarrhoea in 8% of the malaria episodes. Intermittent fever was reported in 98% of the malaria patients with more than one day of fever, compared to 4% of those with other febrile illnesses. Parasite densities greater-than-or-equal-to 10 000/mul were found in 48% of the malaria episodes. Densities greater-than-or-equal-to 400/mul were found in 96% of the malaria episodes and in only 8% of the other febrile illnesses. The 16 malaria episodes (4%) with densities below that level were all in children under one year of age. The ability of the rural medical aid or the doctor to differentiate malaria episodes from other febrile illnesses without microscopical examination was limited. Although very few malaria episodes were missed, substantial over-diagnosis resulted is specificity values of only 13% and 52% for their respective malaria diagnoses. It is concluded that intermittent fever was strongly associated with malaria, but a high accuracy of malaria diagnosis in febrile children requires microscopical examination. Any parasitaemia in children below one year of age, or a parasite density of greater-than-or-equal-to 400/mul in alt children aged 1-9 years, were highly indicative of clinical malaria episodes. Early treatment appeared to prevent mortality from malaria.
