Sentinel surveillance for yellow fever in Kenya, 1993 to 1995.

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Sentinel surveillance for yellow fever in Kenya, 1993 to 1995.

Centers for Disease Control
  • Research Article


Q:\BEV\TERE\EIDPM5\REPRINTS\PER Emerging Infectious Diseases Vol. 2, No. 3—July-September 1996 Dispatches 236 Yellow fever (YF) is an acute mosquito-transmit- ted viral infection, endemic and occasionally epidemic in many countries of Africa and South America. Periodic outbreaks of yellow fever in East Africa have been reported since 1940 (1,2) (Figure 1). The largest outbreak, an estimated 300,000 cases, occurred from 1960 to 1962 in Ethiopia (3). In 1966, YF reappeared in Arba-Minch, Ethiopia, east of Lake Abaya, in an area not affected by the outbreak of 1960 to 1962. During the 1966 outbreak, 2,200 cases (450 deaths) were reported (4). Despite the preva- lence of anti-YF antibody in northern Kenya (up to 14%) (5,6), no outbreaks of YF were reported in Kenya until 1992 when epidemic YF emerged in Kenya for the first time, with at least 54 cases and 29 deaths (7). Cases of hemorrhagic fever were first reported in September 1992, from the southern parts of Keiyo (Kerio Valley), Baringo, and the Koibatek Districts (former Elgeyo-Marakwet and Baringo dis- tricts) in the Rift Valley Province, northwest Kenya (Figure 2). Of the 54 patients with hemorrhagic fe- ver, 35 (67%) were male. Of the 48 patients whose definite age was known, 41 (85%) were 10 to 39 years old. Twenty-one (39%) of the 54 patients had sero- logic evidence of recent YF infection, and three of the 21 had cases confirmed by isolation of YF virus. The outbreak ended when the entire population of these districts was vaccinated. A surveillance sys- tem involving 13 sentinel sites was established 6 months after the epidemic was over. Six health fa- cilities were located within the outbreak area of Keiyo, Koibatek, and Baringo districts. Seven facili- ties were situated in the surrounding areas of Nakuru, Nyandarua, Kericho, and the Uasin Gishu districts. In 1994, the number of sentinel sites was increased to 18. Sentinel facilities were provided with case investigation forms and equipment for blood collection and storage. S

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