The simultaneous estimation of infection rate, cure rate and detectability of parasitic infections is considered. A new method for this estimation based on a simple statistical model assuming constant transition rates between parasite states is proposed. Repeated observations on the infection status of the same individuals is required for this method. A maximum likelihood approach is used for parameter estimation and the calculation of standard errors of the estimates. The method is illustrated by a longitudinal study of the presence of Giardia lamblia infection in Kenyan children.
Of 1270 schoolchildren (651 girls and 619 boys) from 33 urban and rural primary schools in different regions of Kenya who were examined for head lice, 17.1% were infested (8% with living lice or nits, 9.1% with dead nits). The over-all difference between infestation rates in urban and rural schools was not significant, but there was considerable variation in the five different regions selected. Infestation was not sex-related. Infestation rates tended to be higher in older children and in children with longer hair. Negroid children had lower infestation rates than non-Negroid children. The criterion seems to be hair type. Prevalence of infestation was higher in private schools because non-Negroid children predominate in these schools. There was no correlation between infestation and the sharing of a towel or comb, but infestation tended to be higher in those who wash less, in those who share their bed, and in those who sleep with room-mates. Levels of infestation were low, with most harbouring only one or two lice.
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