Rise of multidrug-resistant non-vaccine serotype 15A Streptococcus pneumoniae in the United Kingdom, 2001 to 2014

Conjugate vaccines have reduced the burden of pneumococcal disease in vaccinated children and unvaccinated adults, but emerging non-vaccine serotypes are concerning, particularly if antibiotic resistant. Against this background, we reviewed serotypes and resistance among pneumococci collected via: (i) the British Society for Antimicrobial Chemotherapy (BSAC) bacteraemia and respiratory surveillances from 2001 to 2014; (ii) Public Health England’s (PHE) ‘invasive isolate’ surveillance from 2005 to 2014 and (iii) received as PHE reference submissions from 2005 to 2014. Representatives were sequenced, with sequence types (STs) deduced. Serotype 15A became increasingly prominent in all series, with many representatives showing ‘triple resistance’ to macrolides, tetracyclines and penicillin. In the PHE and BSAC invasive isolates surveillances, serotype 15A was consistently among the 10 most prevalent types from 2011, but never previously; 26-33% of invasive 15A isolates had triple resistance’. BSAC respiratory isolates were only serotyped in the 2013/4 and 2014/5 (October to September years), with 15A proving the most prevalent serotype in both periods, at 9.1 and 10.7% of isolates, respectively, with 38.2 and 47.8% showing triple resistance. Among pneumococci sent to PHE for resistance investigation, the proportion of 15A isolates was 0-4% annually in the years 2005 to 2008 but rose to 29 and 32% in 2013 and 2014, respectively. Almost all multiresistant 15A isolates were sequence type (ST)63 variants, whereas susceptible 15A isolates were clonally diverse. The rise of resistant serotype 15A pneumococci suggests that pneumococcal conjugate vaccines will need ongoing adaptation.