Trends in serotype prevalence in invasive pneumococcal disease before and after infant pneumococcal vaccination in Belgium, 2002-2010.

OBJECTIVES: We evaluated the effect of the infant 7-valent pneumococcal conjugate vaccine (PCV7) program on the serotype distribution in invasive pneumococcal disease in the Belgian population. METHODS: Serotyping was performed on 13,998 bacteraemic and pleural fluid isolates sent to the National Reference Laboratory between 2002 and 2010. We compared the distribution of serogroups (SGs) between the pre- (2002-2004) and post-PCV7 (2007-2010) era for children (<18 years), adults (18-59 years) and older individuals (≥60 years). RESULTS: The proportion of cases caused by PCV7-SGs in subjects <18 years decreased from 69% pre-PCV7 to 26% post-PCV7 (p<0.005) and the majority of cases caused by PCV7-SGs were caused by SG 19. Post-PCV7, the prevalence of PCV7-SGs decreased from 38% to 29% and from 57% to 35% in subjects in the age groups 18-59 and ≥60 years, respectively (p<0.005). Post-PCV7 the prevalence of SGs 1, 7 and 19 increased significantly in subjects aged <18 years. The increase of SG19 was caused by an increase of serotype 19A in this age group (p<0.005). After the introduction of infant PCV7 the largest rise in prevalence occurred for SGs 7, 12 and 22 (p<0.005) in the two older age categories. Post PCV7, the overall PCV13 and 23-valent pneumococcal polysaccharide vaccine coverage rates decreased from 85% to 69% and from 96% to 93%, respectively (p<0.005). CONCLUSIONS: PCV7 has an impact on SG distribution of invasive pneumococcal disease isolates of vaccinated and unvaccinated subjects. SG replacement forms a major threat to the success of PCV7. PCV13, including several additional replacement serotypes (STs 1, 7F, 19A), represents an attractive alternative.

Sequential multiplex PCR assay for determining capsular serotypes of colonizing S. pneumoniae.

BACKGROUND: Asymptomatic nasopharyngeal carriage represents an important biological marker for monitoring pneumococcal serotype distribution and evaluating vaccine effects. Serotype determination by conventional method (Quellung reaction) is technically and financially challenging. On the contrary, PCR-based serotyping represents a simple, economic and promising alternative method. METHOD: We designed a novel multiplex PCR assay for specific detection of the 30 classical colonizing S. pneumoniae serogroups/types. This multiplex assay is composed of 7 consecutive PCR reactions and was validated on a large and recent collection of Streptococcus pneumoniae isolated during a prospective study conducted in Belgium at the time of PCV7 adoption. RESULTS: The multiplex PCR assay allowed the typing of more than 94% of the isolates of a collection of pneumococci isolated from Belgian preschool attendees (n = 332). Seventy-five percent of the isolates were typed after 3 subsequent PCR reactions. Results were in agreement with the Quellung identification. CONCLUSION: Our novel multiplex assay is an accurate and reliable method which can be used in place of the conventional method for S. pneumoniae carriage studies.