Increase in Prevalence of Streptococcus pneumoniae Serotype 6C at Eight Children's Hospitals in the United States from 1993 to 2009

Abstract

Streptococcus pneumoniae serotype 6C, which was described in 2007, causes invasive disease in adults and children. We investigated the prevalence of 6C among pediatric isolates obtained from eight children's hospitals in the United States. S. pneumoniae isolates were identified from a prospective multicenter study (1993 to 2009). Fifty-seven serotype 6C isolates were identified by multiplex PCR and/or Quellung reaction. Five were isolated before 2000, and the prevalence increased over time (P < 0.000001). The median patient age was 2.1 years (range, 0.2 to 22.5 years). Clinical presentations included bacteremia (n ‫؍‬ 24), meningitis (n ‫؍‬ 7), pneumonia (n ‫؍‬ 4), abscess/wound (n ‫؍‬ 3), mastoiditis (n ‫؍‬ 2), cellulitis (n ‫؍‬ 2), peritonitis (n ‫؍‬ 1), septic arthritis (n ‫؍‬ 1), otitis media (n ‫؍‬ 10), and sinusitis (n ‫؍‬ 3). By broth microdilution, 43/44 invasive serotype 6C isolates were susceptible to penicillin (median MIC, 0.015 g/ml; range, 0.008 to 2 g/ml); all were susceptible to ceftriaxone (median MIC, 0.015 g/ml; range, 0.008 to 1 g/ml). By disk diffusion, 16/44 invasive isolates (36%) were nonsusceptible to erythromycin, 19 isolates (43%) were nonsusceptible to trimethoprimsulfamethoxazole (TMP-SMX), and all isolates were clindamycin susceptible. Multilocus sequence typing (MLST) revealed 24 sequence types (STs); 9 were new to the MLST database. The two main clonal clusters (CCs) were ST473 and single-locus variants (SLVs) (n ‫؍‬ 13) and ST1292 and SLVs (n ‫؍‬ 23). ST1292 and SLVs had decreased antibiotic susceptibility. Serotype 6C causes disease in children in the United States. Emerging CC1292 expressed TMP-SMX resistance and decreased susceptibility to penicillin and ceftriaxone. Continued surveillance is needed to monitor changes in serotype prevalence and possible emergence of antibiotic resistance in pediatric pneumococcal disease.

Epidemiology of pneumococcal serotype 6A and 6C among invasive and carriage isolates from Alaska, 1986–2009

“…The presence of 8 STs found among only 27 serotype 6C isolates in this study are consistent with other studies that have described a high degree of genetic diversity among this serotype (Campos et al, 2009;Carvalho et al, 2009;Green et al, 2011;Jacobs et al, 2009;Nunes et al, 2009;Rolo et al, 2011b). Of the 8 STs of serotype 6C isolates reported in this study, 4 (1390, 1379, 473, and 1292) have been previously associated with serotype 6A.…”

“…While ST2899 and ST4285 found in this study are associated solely with serotype 6C, they are double-and triple-locus variants, respectively, of ST1390. Other studies have reported similar findings Green et al, 2011;Jacobs et al, 2009). Among the serotype 6C isolates analyzed by Jacobs et al (2009), 9 MLST clusters were identified.…”

“…Carvalho et al (2009) reported that more than a third of the serotype 6C isolates they analyzed were sequence types associated primarily with serotype 6A isolates. In the study by Green et al (2011), 50% of the serotype 6C isolates analyzed were STs previously associated with serotype 6A. It is interesting to note that among the serotype 6A and 6C isolates analyzed in this study, only isolates of ST473 were found within both serotypes and that ST1390 and ST1379, which are frequently found among serotype 6A isolates, were found exclusively among 6C isolates.…”

“…Since then, there have been a number of reports detailing the prevalence, antimicrobial susceptibility patterns, and genetic diversity among serotype 6C isolates collected from both invasive disease and nasopharyngeal colonization studies (Campos et al, 2009;Carvalho et al, 2009;du Plessis et al, 2008;Green et al, 2011;Hermans et al, 2008;Jacobs et al, 2008Jacobs et al, , 2009Nahm et al, 2009;Nunes et al, 2009;Rolo et al, 2011a;Tocheva et al, 2010). In studies that looked at the prevalence of serotype 6C among invasive and carriage isolates, it was found that anywhere between 5% and 100% of isolates that originally typed as 6A were subsequently identified as serotype 6C (Campos et al, 2009;Carvalho et al, 2009;du Plessis et al, 2008;Hermans et al, 2008;Jacobs et al, 2009;Millar et al, 2010;Rolo et al, 2011a).…”

“…This vaccine confers protection against serotype 6B, and most (Dagan et al, 1996(Dagan et al, , 2002Eskola et al, 2001) but not all (Mbelle et al, 1999) studies have found that PCV7 provides cross-protection against serotype 6A. More recently, IPD data suggest that PCV7 does not provide cross-protection against serotype 6C Green et al, 2011;Millar et al, 2010;Park et al, 2008b). The next-generation pneumococcal conjugate vaccine, PCV13, which contains the PCV7 serotypes plus serotypes 1, 3, 5, 6A, 7F, and 19A, was introduced into the routine vaccination schedule for children in the USA in 2010.…”