Local transmission of Plasmodium vivax malaria in Singapore.

ABSTRACT

A localised outbreak involving 19 cases and two carriers of vivax malaria was reported at Dairy Farm from May to June 1996. Epidemiological investigations showed that the outbreak was caused by the introduction of two foreign workers with imported relapsing vivax malaria into this malaria-receptive area. Transmission of infection occurred amongst 17 other foreign workers residing in the locality and two local residents staying at a condominium nearby. The outbreak was rapidly brought under control through active case finding, isolation and treatment of infected persons, epidemic vector control measures, and improved drainage to prevent Anopheles maculatus breeding. Were it not for the very thorough epidemiological investigations in this episode, foreign workers and local residents with a recent travel history would have been misclassified as imported and the outbreak missed. Medical practitioners should always consider the possibility of malaria in a foreign worker presenting with fever and notify the case as soon as the disease is suspected.

ABSTRACT

PIP As a result of both the constant influx of travellers and foreign workers from endemic countries and the presence of Anopheles vectors, Singapore remains vulnerable to malaria. In May and June of 1996, a localized outbreak involving 19 cases of vivax malaria was reported in central Singapore's Dairy Farm area. Resident in this area at the time were 120 foreign workers employed by and living within two nurseries. Following the outbreak, both epidemiologic and entomologic surveillance studies were conducted. The 19 cases of Plasmodium vivax involved 2 local residents of Dairy Farm Estate condominium and 17 foreign nursery workers (1 Thai, 5 Bangladeshi, and 13 Indian). The origin of the outbreak was traced to 2 foreign workers infected with Plasmodium vivax who defaulted on chloroquine treatment and relapsed within 7 months of arrival in Singapore. Malaria symptoms included fever (100%), rigors (94.7%), chills (89.5%), headache (78.9%), and sweating (42.1%). Larvae of Anopheles maculatus were found in 7 habitats 4 seepages, 1 ground puddle, 1 earth drain, and 1 antimalaria drainage well. Transmission was interrupted within a week after the outbreak was alerted through a comprehensive strategy of active case finding, isolation and treatment of infected persons, epidemic vector control measures, and improved drainage to prevent Anopheles maculatus breeding. Malaria should always be considered in the differential diagnosis of foreign workers who present with fever.