Serotype distribution and antimicrobial susceptibilities of nasopharyngeal isolates of Streptococcus pneumoniae from healthy children in the 13-valent pneumococcal conjugate vaccine era

Characterization of Streptococcus pneumoniae clones from paediatric patients with cystic fibrosis

The role of Streptococcus pneumoniae in cystic fibrosis (CF) is poorly understood. The pneumococcal population has changed over time after the introduction of the heptavalent conjugate vaccine (PCV7) and, more recently, the 13-valent conjugate vaccine (PCV13). Although serotypes and clones causing invasive pneumococcal disease or colonizing healthy children have been extensively analysed, little is known so far on the serotypes and clones of pneumococci in CF patients. The aim of this work was to investigate serotypes, antibiotic susceptibilities, genotypes and biofilm production of CF pneumococcal isolates. Overall, 44 S. pneumoniae strains collected from 32 paediatric CF patients from January 2010 to May 2012 in a large Italian CF Centre were tested for antimicrobial susceptibility testing by Etest, serotyped by the Quellung reaction and genotyped by a combination of different molecular typing methods, including pbp gene restriction profiling, pspA restriction profiling and sequencing, PFGE and multilocus sequence typing. Biofilm production by pneumococcal strains was also assessed. Penicillin non-susceptibility was 16 %. High resistance rates (>56 %) were observed for erythromycin, clindamycin and tetracycline. The most frequent serotype recovered was serotype 3 (31.8 %). The coverage of PCV7 and PCV13 was 6.8 and 47.7 %, respectively. More than 80 % of CF strains belonged to Pneumococcal Molecular Epidemiology Network (PMEN) reference clones, the most common being Netherlands(3)-ST180 (28.2 %), and Greece(21)-30/ST193 (15.4 %). All strains produced biofilm in vitro, although with large variability in biofilm formation efficiency. No correlation was found between biofilm levels and serotype, clone or antibiotic resistance. The high isolation rate of antibiotic-resistant serotype 3 pneumococci from CF patients suggests that PCV13 could increase protection from pneumococcal colonization and infection.

Emergence of serogroup 15 Streptococcus pneumoniae of diverse genetic backgrounds following the introduction of pneumococcal conjugate vaccines in Hong Kong

Serogroup 15 pneumococcal isolates from nasopharyngeal carriage of hospitalized children admitted to a teaching hospital in Hong Kong from April 2009 to September 2013 were characterized by pulse-field gel electrophoresis (PFGE), multilocus sequence typing, and antimicrobial non-susceptibility testing. The overall proportion of serogroup 15 isolates in the pre-PCV7 and post-PCV13 periods rose from 5.7% to 20.0%. The increase in trend for serotype 15B/C was statistically significant among children presented with pneumonia; bronchiolitis; upper respiratory tract infection; and febrile, non-respiratory diseases and for serotype 15A/F, among children with bronchiolitis and febrile, non-respiratory diseases. The predominant PFGE cluster of serotype 15B/C belonged to sequence type (ST) 199. Replacement of this more susceptible cluster (Ery and Tet non-susceptibilities of 32.2% and 25.4%) with the non-susceptible cluster, ST8859 (Ery and Tet non-susceptibilities of 91.7% and 87.5%) was noted. ST63 was the predominant serotype 15A cluster (Ery and Tet non-susceptibilities of 97.4% and 92.3%). Serogroup 15 subtypes have emerged in the post-PCV13 era, and these non-susceptible clusters warrant closer monitoring as candidates for incorporation to future pneumococcal vaccines.

Dynamics of pneumococcal carriage among day-care center attendees during the transition from the 7-valent to the higher-valent pneumococcal conjugate vaccines in Greece

BACKGROUND

In Greece recently, higher-valent pneumococcal conjugate vaccines (PCVs) replaced the 7-valent (PCV7); the 10-valent (PCV10) became available in May 2009 and the 13-valent (PCV13) in June 2010.

METHODS

We investigated the nasopharyngeal colonization with Streptococcus pneumoniae in day-care center attendees in Athens and the prefecture of Viotia. Between December 2010 and June 2011, nasopharyngeal cultures were obtained 4 times, at enrollment and then every 6 to 8 weeks.

RESULTS

Among the 233 children, 225 (96.6%) had been vaccinated with ≥1 dose of PCV7. One tenth of the PCV7 vaccinated attendees had also received ≥1 dose of PCV13 or PCV10. During the 4 samplings, 358 isolates were recovered from a total of 874 samples. Of the 233 children, 183 (78.5%) were found to carry S. pneumoniae at least once. The overall serotype distribution among carriers was similar regardless of the time lapsed since the last PCV7 dose. A high frequency of 19A (17.1%) coincided with a low frequency of 19F (1.4%). Non-PCV13 serotypes accounted for 73.1% of the isolates; 23B, 15B/C, 16F, 21, 11A, 15A, 6C, 10A, 22F and 23A were the most common. Among attendees aged 24-59 months (median age 42 months), prolonged carriage of a non-PCV13 serotype was relatively common, mainly for 21 and 16F. One out of 4 cases of colonization with the prevalent non-PCV13 serotypes was followed by persistent carriage for 5 to 14 weeks.

CONCLUSIONS

During this period of transition to the higher-valent PCVs in the day-care center setting, non-PCV13 serotypes dominated and exhibited prolonged colonization. The frequency and the duration of prolonged carriage tends to be increased, if sampling frequency increases and the carriage time before and after positive cultures is taken into consideration. Further studies regarding the fitness of the colonizing non-PCV13 serotypes will likely to be seen in the future.

Near-elimination of otitis media caused by 13-valent pneumococcal conjugate vaccine (PCV) serotypes in southern Israel shortly after sequential introduction of 7-valent/13-valent PCV

BACKGROUND

Otitis media (OM) is common in early childhood. Streptococcus pneumoniae caused approximately 30%-60% of episodes before the pneumococcal conjugate vaccine (PCV) era. The 7-valent PCV (PCV7) was introduced to the Israeli National Immunization Plan in July 2009, and was gradually replaced by the 13-valent PCV (PCV13) starting in November 2010. We aimed at assessing the impact of PCV7/PCV13 sequential introduction on pneumococcal and overall OM necessitating middle ear fluid culture in children aged <2 years in southern Israel.

METHODS

This was a prospective, population-based, active surveillance. Our medical center is the only one in the region, enabling incidence calculation. All pneumococcal episodes submitted for culture between July 2004 and June 2013 were included. Three subperiods were defined: pre-PCV, PCV7, and PCV13.

RESULTS

Overall, 6122 OM episodes were recorded, and 1893 were pneumococcal. Compared with the pre-PCV period, OM caused by PCV7 plus serotype 6A and the 5 additional PCV13 serotypes (5VT : 1, 3, 5, 7F, 19A) decreased by 96% and 85%, respectively (incidence rate ratios [IRRs], 0.04 [95% confidence interval {CI}, .02-.08] and 0.15 [95% CI, .07-.30], respectively) in a 2-step pattern: In the PCV7 period, only OM caused by PCV7 + 6A serotypes was decreased; in the PCV13 period, 5VT OM rates decreased, along with an additional PCV7 + 6A OM reduction. A nonsignificant increase in non-PCV13 serotype OM was observed (IRR, 1.07 [95% CI, .72-1.58]). In total, 77% and 60% reductions of all-pneumococcal and all-cause OM incidences, respectively, were observed.

CONCLUSIONS

A substantial 2-step reduction of pneumococcal OM rates, with near-elimination of PCV13 disease, was observed shortly after PCV7/PCV13 introduction.