The changing age structure of diphtheria patients: evidence for the effectiveness of EPI in the Sudan.

During an outbreak of diphtheria in Khartoum, Sudan, in 1988, only 19.1% of patients admitted to hospital were under 5 years of age. This is considerably less than the proportion of such patients seen during a similar outbreak in Khartoum in 1978 (49.5%) and also less than the proportion (55.2%) of under-5-year-olds reported for all inpatients with diphtheria in the Sudan during 1979-86. Cluster surveys carried out between 1981 and 1989 demonstrate that vaccination coverage was much higher for under-5-year-olds (about 65% for the third dose of diphtheria-pertussis-tetanus vaccine (DPT3] than for children of school age (less than 20% for DPT3) at the time of the 1988 outbreak. These results indicate that improved vaccination coverage led to the shift in the age distribution of diphtheria patients seen during the 1988 outbreak. It is unlikely that these data are affected by the type of biases that usually plague disease surveillance systems and can therefore be used as a simple way of assessing the effectiveness of the Expanded Programme on Immunization (EPI).