Molecular epidemiology of diphtheria.

Molecular subtyping of Corynebacterium diphtheriae identified significant genetic diversity within the species and led to the identification of a unique clonal group that emerged in Russia in 1990 at the beginning of the current epidemic. Strains of this group belong to a distinct electrophoretic type complex and are of ribotypes D1 and D4. Identification of the group allowed for precise monitoring of the epidemic's progression and for rapid detection of cases imported to other countries. The evolution of this clonal group was monitored, and changes were identified. Molecular analysis revealed that no amino acid substitutions have occurred in the diphtheria toxin gene of the epidemic clone strains, reaffirming the use of the current vaccine as the single most effective preventive measure. Application of molecular subtyping methods and continuous monitoring of the spread of these clones has made it possible to distinguish rapidly between epidemic, endemic, and imported cases, allowing for implementation of timely and adequate preventive measures and providing reassurance that no secondary spread resulted from importations.