Low prevalence of Corynebacterium Diphtheriae carriers in Italian schoolchildren

In Italy, the prevalence of Corynebacterium diphtheriae carriage is unknown. Throat swabs from 1970 healthy children, 6 to 14 years of age, were investigated. Three non-toxigenic strains of Corynebacterium diphtheriae biotype mitis, were isolated from as many healthy children. Molecular characterization of the these strains indicates that they have been persisting for at least 25 years and are endemic rather than having been imported from countries with current endemic or epidemic diphtheria. Although non-toxigenic strains of C. diphtheriae occurring in the community are usually thought to be of little or no epidemiological importance, it may be possible to convert a non-toxigenic diphtheria strain into a toxigenic one by lysogenization with a specific temperate bacteriophage. Despite the virtual elimination of diphtheria in Italy, this long-standing circulation of non-toxigenic C. diphtheriae poses a potentially significant risk to public health and could result in the re-emergence of diphtheria in our country, even though the high proportion of younger population with protective levels of immunity is probably significant in preventing diphtheria spread. Therefore, it is important to maintain mandatory vaccination in childhood and to offer periodical re-vaccination of adults.