Patterns of transmission and severity of measles infection: a reanalysis of data from the Machakos area, Kenya.

Data on measles from the project in the Machakos District, Kenya, 1974-1981, were reanalyzed. In families with several cases, secondary cases (children infected in the home) had a relative mortality risk of 3.00 (95% confidence interval [CI]: 1.55-5.80) compared with index cases who caught infection from someone outside the home. The case fatality rate (CFR) may be higher among secondary cases exposed to two or more index cases than among those exposed to only one index case (relative risk [RR] = 2.47; 95% CI: 0.93-6.56). The CFR was also higher among secondary cases exposed to a fatal index case than among those exposed to an index case who survived (RR = 4.69; 95% CI: 1.64-13.41). Children aged 12-23 months and those greater than or equal to 5 years were more likely than other age groups to have been infected by someone outside the home. During the course of the project the CFR in families with several cases was reduced from 8.8% to 2.7%. Though there is no general explanation for this tendency, it was observed that the proportion of secondary cases per index case was reduced during the last part of the project (odds ratio = 0.73; 95% CI: 0.56-0.95).