First recorded outbreak of yellow fever in Kenya, 1992-1993. I. Epidemiologic investigations.

Outbreaks of yellow fever (YF) have never been recorded in Kenya. However, in September 1992, cases of hemorrhagic fever (HF) were reported in the Kerio Valley to the Kenya Ministry of Health. Early in 1993, the disease was confirmed as YF and a mass vaccination campaign was initiated. Cases of suspected YF were identified through medical record review and hospital-based disease surveillance by using a clinical case definition. Case-patients were confirmed serologically and virologically. We documented 55 persons with HF from three districts of the Rift Valley Province in the period of September 10, 1992 through March 11, 1993 (attack rate = 27.4/100,000 population). Twenty-six (47%) of the 55 persons had serologic evidence of recent YF infection, and three of these persons were also confirmed by YF virus isolation. No serum was available from the other 29 HF cases. In addition, YF virus was isolated from a person from the epidemic area who had a nonspecific febrile illness but did not meet the case definition. Five patients with confirmed cases of YF died, a case-fatality rate of 19%. Women with confirmed cases of YF were 10.9 times more likely to die than men (P = 0.010, by Fisher's exact test). Of the 26 patients with serologic or virologic evidence of YF, and for whom definite age was known, 21 (81%) were between 10 and 39 years of age, and 19 (73%) were males. All patients with confirmed YF infection lived in rural areas. There was only one instance of multiple cases within a single family, and this was associated with bush-clearing activity. This was the first documented outbreak of YF in Kenya, a classic example of a sylvatic transmission cycle. Surveillance in rural and urban areas outside the vaccination area should be intensified.

Viral etiology and epidemiology of acute respiratory infections in children in Nairobi, Kenya.

Acute respiratory infection (ARI) is the most common cause of illness and death in young children worldwide. Because of inadequate laboratory facilities and financial resources the etiological agents responsible for most cases in developing countries remain unknown, thus obviating appropriate management. Therefore, an ARI program was commenced at the Kenyatta National Hospital, Nairobi, Kenya in 1981 with the objectives of establishing the microbial causes, clinical presentations, and diagnoses of ARI in children under 5 years of age and of developing simple, rapid, and inexpensive diagnostic techniques. Viruses were demonstrated in 54% of the 822 children studied, but over half of the viruses identified were types not commonly associated elsewhere with the causation of severe ARI. Respiratory syncytial, parainfluenza, and adenoviruses occurred in the same age groups and during similar weather conditions as elsewhere. Measles virus occurred most frequently in those 7 to 9 months old. Herpes simplex, rhino-, and enteroviruses play causative roles in some cases of severe ARI in Kenyan children. A combination of immunofluorescent and cell culture techniques were shown to be essential for the detection of viruses.

Investigation of the effectiveness of measles vaccination in children in Kenya.

Laboratory studies were performed on 128 children clinically diagnosed as measles when seen at the Infectious Diseases Hospital, Kenyatta National Hospital (IDH), Nairobi (86 cases) and the Rural Health Training Centre, Maragua, Central Province (42 cases) between 9 July and 31 August 1984. A concurrent measles infection was confirmed in 95% of the children seen at IDH and in 85% of those seen at Maragua, with similar proportions of confirmations in children who had, and who had not, received measles vaccine. No differences in the number of sero-conversions nor in the absolute levels of acute or convalescent HI antibody titres could be detected between vaccinated and unvaccinated children. Analysis of the cases seen at Maragua indicates that about two thirds of the children who had received vaccine were protected. A pilot study of vaccinating children at 8 months and again at 12-13 months is suggested in an attempt to eradicate measles.

Herpes simplex virus in clinically suspected chancroid in Nairobi, Kenya.

PIP: Of 110 males selected for review with possible chancroid, 96 were clinically diagnosed as having chancroid, 7 as having herpetic lesions, and 7 as having syphilis. Of the 96 patients diagnosed clinically as chancroid, 76 (79.2%) were culture positive for H. ducreyi. 9 (9.4%) of these 96 patients yielded Herpes Simplex Virus (HSV). Both HSV and H. ducreyi were isolated from 5 of the patients, and from 4 of the patients HSV alone was isolated. 7 patients (6.4%) were clinically diagnosed as having herpetic ulcers. 5 of these grew HSV. Overall, 14 of the 110 patients (12.7%) yielded HSV. 1 patient, who presented with small vesicular lesions characteristic of HSV, yielded the virus on culture. The vesicles were initially negative for H. ducreyi, but 6 days later he had developed deep purulent ulcers in the same sites as the vesicular lesions and became culture positive for H. ducreyi snd HSV-negative. The possible association between HSV and chancroid is discussed in the light of these findings and comparisons made between the results of the present study and earlier findings made in Kenya and elsewhere, with suggestions being given as to the reasons for the apparent differences. The HSV isolation techniques used in this study may be less sensitive than those used in other studies, but it is highly unlikely that this possibility alone accounts for all of the observed differences. Patients with hepetic ulcers may be less likely to present early in the course of the disease, if at all, believing the infection to be minor and one that will heal on its own. It is also possible that HSV infection is less common in Kenya, either alone or as an initiator of chancroid, than in the US or Europe, becuase of a higher rate of childhood HSV infections in Kenya, which may confer a degree of immunity against genital HSV infection in this population. The lower prevalence of HSV in association with H. ducreyi reported may be at least partly the result of a much higher incidence in Kenya of chancroid which is not initiated by HSV. A higher incidence of HSV genital infection in Europe and America would also make it more likely that HSV would fortuitously be isolated more frequently from H. ducreyi positive lesions.^ieng

Recovery of o'nyong-nyong virus from Anopheles funestus in Western Kenya.

O'nyong-nyong (ONN) virus first appeared nearly 20 years ago and was responsible for one of the largest arbovirus outbreaks ever documented. Since the original outbreak ended, ONN activity, as determined serologically, gradually declined on the Kano Plain in western Kenya. In June, 1978, a virus similar or identical to ONN was isolated from a pool of Anopheles funestus Giles captured at Ahero on the Kano Plain. The possible implications of this isolation are discussed.