Falciparum malaria as a cause of fever in adult travellers returning to the United Kingdom: observational study of risk by geographical area.

BACKGROUND The probability that a returned traveller with a history of fever has malaria is likely to vary by geographical area, but this has not been quantified in travellers. AIM To collect data on prevalence of malaria in outpatients returning with a fever or history of fever from malaria-endemic countries, at the point of presentation for a malaria test. DESIGN Observational retrospective study. Consecutive patients presenting to an unselected 'walk-in' clinic for returned travellers. RESULTS Of 2867 patients meeting inclusion criteria, 337 (11.8%) had malaria, 89.5% originating in sub-Saharan Africa. Of travellers returning from sub-Saharan Africa excluding South Africa with fever/history of fever, 291/1497 had malaria (19.4%, 95% CI 17-21%). A high proportion was visiting friends and relatives. In those from other areas the proportions were: 16/707 (2.3%, 95% CI 1.5-3.8) from Indian subcontinent/Southeast Asia; 2/143 (1.4%) from Southern America; 4/129 (3.1%) from South Africa; 1/44 (2.3%) from North Africa; and 8/41 (19.5%) from Oceania. Compared to other malaria-endemic regions, African travel gave an adjusted odds ratio of 7.8 (95% CI 5.4-11.2, P < 0.0001). Only 45.1% of malaria cases had a fever (> or =37.5 degrees C) at the time of presentation. Only 3% of all diagnoses of malaria had no history of fever. In 28% of cases parasite count increased in the initial 24 h of antimalarial treatment. CONCLUSION The likelihood that a patient with fever returning from Africa has malaria is high (around 1 in 5), and is significantly lower from other areas. Absence of fever at presentation does not exclude malaria.