RESUMO
BACKGROUND: Multilocus sequence typing (MLST) is used to gain insight into the population genetics of bacteria in the form of sequence type (ST). MLST has been used to study the evolution and spread of virulent clones of Streptococcus pneumoniae in many parts of the world. Such data for S. pneumoniae are lacking for the countries of the Arabian Peninsula, including Kuwait. METHODS: We determined the STs of all 31 strains of S. pneumoniae from invasive diseases received at a reference laboratory from various health centers in Kuwait during 2018 by MLST. The relationship among the isolates was determined by phylogenetic analysis. We also determined the serotypes by Quellung reaction, and antimicrobial susceptibility by Etest, against 15 antibiotics belonging to 10 classes. RESULTS: There were 28 STs among the 31 isolates, of which 14 were new STs (45.2%) and 5 were rare STs (16.1%). Phylogenetic analysis revealed that 26 isolates (83.9%) were unrelated singletons, and the Kuwaiti isolates were related to those from neighboring countries whose information was gleaned from unpublished data available at the PubMLST website. Many of our isolates were resistant to penicillin, erythromycin, and azithromycin, and some were multidrug-resistant. Virulent serotype 8-ST53, and serotype 19A with new STs, were detected. CONCLUSIONS: Our study detected an unusually large number of novel STs, which may indicate that Kuwait provides a milieu for the evolution of novel STs. Novel STs may arise due to recombination and can result in capsular switching. This can impact the effect of vaccination programs on the burden of invasive pneumococcal disease. This first report from the Arabian Peninsula justifies the continuous monitoring of S. pneumoniae STs for the possible evolution of new virulent clones and capsular switching.
RESUMO
Kuwait started immunizing children <2 y age with the 7-valent pneumococcal conjugate vaccine, PCV7 from August 2007. PCV7 was replaced by the 13-valent conjugate vaccine, PCV13 from August 2010. In a previous analysis of the results for the period, August 2010-July 2013 (period II), there was no evidence of serotype-specific protection for invasive disease against the additional six serotypes to PCV7 present in PCV13 (non-PCV7 serotypes) as evidenced by isolation from blood and cerebrospinal fluid in any of the age groups, <2 y, 2-5 y, 6-50 y, 51-65 y, and >65 y and all ages, compared to the pre-vaccination period, August 2003-July 2006 (period I). In the current study, we allowed additional time, August 2013-July 2019 (period III) for better vaccine effect and repeated the analysis. We did not find any significant decrease of invasive disease due to the non-PCV7 serotypes of PCV13 in period III and combined II and III periods compared to period I. However, these comparisons showed significant reductions for four of the six and total serotypes of PCV7, and total serotypes of PCV13. Reduction for total PCV13 serotypes was contributed by serotypes of PCV7. It appears that the six non-PCV7 serotypes in PCV13 do not offer much protection. Some contributory factors for the poor effect of the non-PCV7 serotypes may be related to few cases with underpowered statistical analysis, lack of vaccine coverage data, method of vaccine efficacy analysis based on vaccine serotypes relative to all serotypes and unusual rise in non-typeable isolates post vaccination that would have masked true serotypes.