The changing epidemiology of diphtheria in the vaccine era.

The epidemic of diphtheria in the Newly Independent States (NIS) of the former Soviet Union has drawn attention to our incomplete understanding of the epidemiology of diphtheria. Many unanswered questions remain concerning the reasons for a resurgence of diphtheria and for the shift in the age of patients and concerning the mechanisms for acquisition of immunity in adults through natural infection under unfavorable living conditions. Other unanswered questions relate to the precise role of socioeconomic factors and hygiene conditions in the initiation, buildup, and spread of the epidemic. Important characteristics of the NIS epidemic can be used to help predict the spread of future diphtheria epidemics. These characteristics include a high proportion of infected adults, a progressive spread of disease from urban centers to rural areas, and transition from initial amplification of disease in groups with high rates of close contacts in focalized, well-distinguished outbreaks to a more generalized epidemic.