Gender and the pattern of transmission of measles infection. A reanalysis of data from the Machakos area, Kenya

Summary

Data on measles from the project in the Machakos district, Kenya between 1974 and 1981 have been reanalysed in order to test the impact of sex and cross-sex transmission on severity of infection. In families with several cases, the case fatality rate was as high as 11.3% (13/115) during the initial 6 months of the project. In the remaining period, the case fatality rate fell to 2.4% (21/885) (relative risk (RR) = 0.21, 95% confidence interval (CI): 0.11–0.39). During the initial period with high mortality, second cases had 4.74 times higher mortality (95% CI: 1.65–13.66) than index cases and there was no difference in mortality between girls and boys (RR = 0.98). Among secondary cases, though not significant, those infected by someone of the opposite sex had a trend toward a higher risk of dying than those infected by someone of their own sex (RR = 2.44, 95% CI: 0.77–7.78). In families with two children of the same sex, the case fatality rate was 9% compared with 29% in families with a boy and a girl (RR = 3.49; 95% CI: 0.96–12.75). In the subsequent period with low mortality, the difference in mortality between index and secondary cases was less pronounced (RR = 2.32, 95% CI: 1.03–5.25) and girls had significantly higher case fatality than boys (RR = 2.63, 95% CI: 1.09–6.34). There was no difference in this case fatality rate associated with cross-sex transmission of infection (RR = 0.88). Throughout the study period, girls had a higher risk than boys of getting infected by someone of the opposite sex (RR = 1.26, 95% CI: 1.03–1.55). There is no explanation of why the decline in case fatality was greater among boys, so that girls obtained significantly higher mortality.