Streptococcus pneumoniae serotype 3 in Mexico (1994-2017): decrease of the unusual CC4909 lineage post-PCV13 introduction

Streptococcus pneumoniae expressing serotype 3 have high virulence and case fatality ratio. Most studies of serotype 3 pneumococci have focused on a single lineage, the widespread ST180. To evaluate the serotype 3 lineages causing infections in Mexico we characterized 196 isolates recovered in 1994-2017. The isolates were mostly susceptible to all antimicrobials tested. A single meningitis isolate was resistant to penicillin and resistance to erythromycin was 5.2%. The isolates represented the widely disseminated clonal complex CC180 (n=140), the unusual CC4909 (n=42), CC260 (n=11), and a few singletons (n=3). CC260 was less frequent among pneumococcal invasive disease isolates than CC180 and CC4909 (p=0.015). There was a decrease of CC4909 (p