Pneumococcal Serotypes Causing Acute Otitis Media Among Children in Barcelona (1992–2011): Emergence of the Multiresistant Clone ST320 of Serotype 19A

Abstract

Background: There is scarce information about changes in serotypes and clonal types of Streptococcus pneumoniae causing acute otitis media (AOM) in recent years, particularly in European countries. Methods: Pneumococcal serotypes and clones from S. pneumoniae strains isolated from children with AOM who were attended at Hospital Sant Joan

de Déu, Barcelona (1992 to 2011), were studied. Heptavalent pneumococ- cal conjugate vaccine (PCV7) was introduced in June 2001. We defined 3

periods: prevaccine period 1992 to 2001, early vaccine period 2002 to 2006 and late vaccine period 2007 to 2011. Results: There were 376 pneumococcal strains causing AOM, and 373 (99.2%) of them were serotyped. AOM caused by PCV7 serotypes declined significantly: 161 of 245 (65.7%) episodes in 1992 to 2001 versus 22 of 67 (32.8%) in 2002 to 2006 versus 8 of 61 (13.1%) in 2007 to 2011 P < 0.001. In the last period (2007 to 2011), the potential serotype coverage for

the PCV10 was 16.4% and for the PCV13 was 68.9% (P < 0.001). Sero- type 19A increased from 5.7% in 1992 to 2001 to 42.6% in 2007 to 2011

(P < 0.001). Among strains with penicillin minimal inhibitory concentra- tion ≥0.12 μg/mL (n = 241), serotype 19A rose from 2.3% in the first period

to 57.9 % in the last period (P < 0.001). The clonal-type ST320 was initially detected in 2005, and in the period 2007 to 2011, the ST320 was found in 72.7% of nonsusceptible serotype 19A isolates.

Conclusions: Among children with AOM, a rapid expansion of the mul- tiresistant clone ST320 expressing serotype 19A has been observed in Bar- celona. The implementation of PCV13, which includes this serotype, may

decrease the prevalence of AOM and reduce antimicrobial resistance.