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Molecular epidemiology of C. diphtheriae strains during different phases of the diphtheria epidemic in Belarus

DOI: 10.1186/1471-2334-6-129

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The biotype and toxigenicity status of 3513 C. diphtheriae strains isolated from all areas in Belarus during a declining period of diphtheria morbidity (1996–2005) was undertaken. Of these, 384 strains were isolated from diphtheria cases, 1968 from tonsillitis patients, 426 from contacts and 735 from healthy carriers. Four hundred and thirty two selected strains were ribotyped.The C diphtheriae gravis biotype, which was prevalent during 1996–2000, was "replaced" by the mitis biotype during 2001–2005. The distribution of toxigenic C. diphtheriae strains also decreased from 47.1% (1996) to 5.8% (2005). Changes in the distribution of the epidemic ribotypes Sankt-Peterburg and Rossija were also observed. During 2001–2005 the proportion of the Sankt-Peterburg ribotype decreased from 24.3% to 2.3%, in contrast to the Rossija ribotype, that increased from 25.1% to 49.1%. The circulation of other toxigenic ribotypes (Otchakov, Lyon, Bangladesh), which were prevalent during the period of high diphtheria incidence, also decreased. But at the same time, the proportion of non-toxigenic strains with the Cluj and Rossija ribotypes dramatically increased and accounted for 49.3% and 30.1%, respectively.The decrease in morbidity correlated with the dramatic decrease in the isolation of the gravis biotype and Sankt Peterburg ribotype, and the prevalence of the Rossija ribotype along with other rare ribotypes associated with non-toxigenic strains (Cluj and Rossija, in particular).The diphtheria epidemic, which emerged in the 1990's in the newly independent states (NIS) of the former Soviet Union, was also reported from Belarus. In Belarus, 794 diphtheria cases were identified during 1990–1995, of which 25 were fatal. As a consequence of mass immunization the morbidity stabilized in 1996. In 2005 the morbidity decreased to 0.11 per 100 000 population with a morbidity index of 0.1/100 000 population in advance of the WHO target for 2010. However, the diphtheria incidence in Belarus rema


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