• Vol. 38 No. 10, 840–849
  • 15 October 2009

Epidemiological Characteristics of Imported and Locally-acquired Malaria in Singapore

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ABSTRACT

Introduction: The objective of the study was to determine the trend of malaria, the epidemiological characteristics, the frequency of local transmission and the preventive and control measures taken. Materials and Methods: We analysed the epidemiological records of all reported malaria cases maintained by the Communicable Diseases Division, Ministry of Health, from 1983 to 2007 and the Anopheles vector surveillance data collected by the National Environment Agency during the same period. Results: The annual incidence of reported malaria ranged from 2.9 to 11.1 per 100,000 population, with a sharp decline observed after 1997. There were 38 deaths, 92.1% due to falciparum malaria and 7.9% due to vivax malaria. Of the reported cases, 91.4% to 98.3% were imported, with about 90% originating from Southeast Asia and the Indian sub-continent. Among the various population groups with imported malaria, the proportion of cases involving work permit/employment pass holders had increased, while that of local residents had decreased. Between 74.8% and 95.1% of the local residents with imported malaria did not take personal chemoprophylaxis when they travelled overseas. Despite the extremely low Anopheles vector population, a total of 29 local outbreaks involving 196 cases occurred. Most of the larger outbreaks could be traced to foreign workers with imported relapsing vivax malaria and who did not seek medical treatment early. One of the outbreaks of 3 cases in 2007 was caused by Plasmodium knowlesi, a newly recognised simian malaria which was probably acquired in a forested area where long-tail macaques had been sighted. Conclusions: Singapore remains both vulnerable and receptive to the reintroduction of malaria and a high level of vigilance should be maintained indefinitely to prevent the re-establishment of endemicity. Medical practitioners should highlight the risk of malaria to travellers visiting endemic areas and also consider the possibility of simian malaria in a patient who has no recent travel history and presenting with daily fever spikes and with malaria parasite morphologically similar to that of P. malariae.


Malaria used to be endemic in Singapore. In the early 1900s, almost 3000 malaria-related deaths were reported annually. Malaria control started in 1911 with the construction of a comprehensive drainage system. Together with an anti-larval oiling programme, malaria was rapidly put under control. Unfortunately, these measures broke down during World War II resulting in a resurgence of malaria. After the war, malaria was once again brought under control and it was believed that local transmission of malaria had ceased.1 In 1964, a local outbreak of 29 cases occurred at Fuyong estate.2 This led to a comprehensive review of the existing malaria control strategies. In the 1970s, rapid and massive land development and the influx of large numbers of foreign workers from malarious countries provided favourable epidemiological conditions for local transmission of malaria with a very large outbreak of 82 cases reported at Whampoa-Kallang in 1974 to 1975.3 Consequently, epidemiological and vector surveillance activities were further strengthened. In November 1982, Singapore was certified malaria-free by the World Health Organization (WHO). This milestone was achieved as WHO was confident that Singapore’s comprehensive health service networks in the urban settings with its effective malaria vigilance mechanism would be adequate to prevent the re-establishment of endemic malaria in the infinite future.4

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