Temporal trends and clonal diversity of penicillin non-susceptible pneumococci from meningitis cases from 1996 to 2012, in Salvador, Brazil.

Background: Hospital-based surveillance for pneumococcal meningitis has been conducted since January 1996 in the city of Salvador, Brazil. The purpose of this study was to describe the temporal evolution of Penicillin Non-Susceptible Streptococcus pneumoniae (PNSSP) in regards to serotype distributions and clonal diversity recovered from meningitis cases over 17 years.
Methods: Broth microdilution was used to identify pneumococcal isolates that were PNSSP (Minimum Inhibitory Concentration > 0.12 μg/ml). The annual incidence rate of meningitis cases was calculated. Serotyping was defined using multiplex polymerase chain reaction assays and quellung reaction. Genetic diversity of PNSSP isolates was assessed using both pulsed-field gel electrophoresis (PFGE) and Multilocus Sequence Typing (MLST) analyses.
Results: A total of 854 cerebrospinal fluid (CSF) culture pneumococcal isolates were tested by broth microdilution method and serotyped. A total of 173 (20.3%) were penicillin non-susceptible (PNSSP) (Minimum Inhibitory concentration ≥ 0.12 μg/ml). The annual incidence of meningitis cases declined from 1.65/100,000 population (1996) to 0.2/100,000 population in 2012 and the rate due to PNSSP declined 82% over the 17-years of surveillance. PNSSP isolates were restricted to 13 serotypes, being the most common ones serotypes 14 (45.1%; 78/173), 23 F (19.1%; 33/173), 6B (14.4%; 25/173), 19 F (9.2%; 16/173) and 19A (5.2%; 9/173). Among the PNSSP isolates, 94% had serotypes represented in the 10-valent conjugate vaccine (PCV10). The predominant serotype 14 clonal groups were identified as PFGE group A/multilocus sequence type 66 (ST66) [35.3% (61/173)] and PFGE group GK/ST156 [4.6% (8/173)], the latter one associated with high level resistance to penicillin and ceftriaxone.
Conclusions: Our results show sustained reductions in pneumococcal meningitis cases in the Metropolitan region of Salvador from 1996 to 2012. This might reflect a beneficial impact of conjugate vaccines. Continued surveillance and further studies need to be conducted to better understanding on PCV10 vaccine impact.