Characterisation of invasive Haemophilus influenzae isolates in Slovenia, 1993-2008

The objectives of our study were to describe the epidemiology of invasive Haemophilus influenzae disease from 1993 to 2008 in Slovenia, a country with routine H. influenzae serotype b (Hib) conjugate vaccination since the year 2000. A total of 292 isolates of H. influenzae, recovered from a normally sterile site, were collected in the study period. The isolates were serotyped by slide agglutination and antibiotic susceptibility was determined. One hundred and eight isolates received after the year 2000 were serotyped by slide agglutination and by polymerase chain reaction (PCR) capsule typing, and both methods were compared. After the introduction of the routine Hib vaccination, the incidence of H. influenzae disease in children under the age of 5 years has decreased by 87.6% and type b was replaced by non-typeable H. influenzae as the predominant serotype. The proportion of serotype b decreased from 85.3% in the pre-vaccination period to 13.0% in the vaccination period and the proportion of non-capsulated isolates increased from 12.0 to 85.2%. The study of genetic relatedness by pulsed-field gel electrophoresis (PFGE) demonstrated that the isolates of serotypes b and f were genetically homogeneous within the serotype. The results of our national surveillance showed that the vaccine has been very efficient in preventing Hib invasive disease in Slovenia. Nevertheless, we see a need for further monitoring of invasive H. influenzae infections at a national level.