Demographic characteristics of the Lambwe Valley population.

Thirty-four per cent of the population (11,079) in the Lambwe Valley study site was under the age of 10, and 59% were under the age of 20. The population was equally divided among males and females (M/F 0.99). The crude birth rate averaged 45%; the death rate was 8% and the natural increase averaged 37%. Infant and child mortality was 66% and 108% respectively. The average household size was 8.4 individuals. The population migrated to the Lambwe Valley primarily from other areas in Kenya, although 13% were from Tanzania. The predominant tribal group was Luo (59%) followed by the Abasuba (38%). A few Luyha and Kisii were also encountered. Population increased by 3.5-fold in the 1960s, followed by a 2.5-fold increase in the 1970s. Due to an aerial spray tsetse control programme, sleeping sickness had a low prevalence in October 1981 (one of 5749). Of 339 individuals confirmed as sleeping sickness patients by hospital records from within the study site 320 (94.3%) were traced to their homes. Mortality in domestic cattle (40%), goats (47%), sheep (55%), and dogs (50%) had occurred over the previous two years during an outbreak of trypanosomiasis.