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Locally Acquired Malaria Cases in Riyadh, Saudi Arabia.


There have been no reports of vector-borne malaria transmission in Riyadh for more than 15 years. When we were notified of two Plasmodium falciparum cases in children who had not left Riyadh, we began an entomological and epidemiological investigation to determine how these children acquired malaria.


We reviewed all malaria cases reported in Riyadh between November 1991 and February 1992. For each case with no prior blood transfusion or travel to a malarious area, we visited the patient's house, took a history of exposure and of febrile illness from the family and searched for Anopheles mosquitoes by indoor home collection using space spray sheets, by indoor and outdoor light traps and by direct night catch from human baits. We compared eight case houses with 40 randomly selected control houses within 400 meters. Known mosquito breeding areas in the city were searched for larvae.


We identified nine cases of acute P. falciparum malaria with no history of blood transfusion or of travel to a malarious area during the preceding three months. We were able to find the houses of eight of the cases. These houses were widely scattered with > 2 km. between the closest. The median age was 2 years. No other family members had had confirmed malaria or a prolonged febrile illness. We found no Anopheles adults or larvae in or around the houses. Families of cases were not more likely to report exposure to mosquitoes than control families. All eight case-patients had been admitted to a hospital during the month before the onset of malaria, while none of the 40 children of similar age and sex from control houses had (O.R. infinity; P<0.05 Fisher's exact test).


There is no evidence for local vector-borne malaria in Riyadh. Transmission was apparently nosocomial. Further case investigations should include questions about previous hospital exposure.