The Evolving Epidemiology of Serotype Distribution and Antimicrobial Resistance of Streptococcus pneumoniae Strains Isolated from Adults in Crete, Greece, 2009–2016

BACKGROUND: Pneumococcal disease is a major cause of morbidity and mortality worldwide, especially in patients with comorbidities and advanced age. This study evaluated trends in epidemiology of adult pneumococcal disease in Crete, Greece, by identifying serotype distribution and antimicrobial resistance of consecutive Streptococcus pneumoniae strains isolated from adults during an 8-year time period (2009–2016) and the indirect effect of the infant pneumococcal higher-valent conjugate vaccines 10-valent pneumococcal conjugate vaccine (PCV10) and 13-valent pneumococcal conjugate vaccine (PCV13). MATERIALS AND METHODS: Antimicrobial susceptibility was performed by E-test and serotyping by Quellung reaction. Multidrug resistance (MDR) was defined as non-susceptibility to penicillin (PNSP) combined with resistance to ≥2 non-β-lactam antimicrobials. RESULTS: A total of 135 S. pneumoniae strains were isolated from adults during the study period. Twenty-one serotypes were identified with 17F, 15A, 3, 19A, and 11A, being the most common. The coverage rates of PCV10, and PCV13 were 17.8% and 37.8%, respectively. PCV13 serotypes decreased significantly from 68.4% in 2009 to 8.3% in 2016 (P = 0.002). The most important emerging non-PCV13 serotypes were 17F, 15A, and 11A, with 15A being strongly associated with antimicrobial resistance and MDR. Among all study isolates, penicillin-resistant and MDR strains represented 7.4% and 14.1%, respectively. Predominant PNSP serotypes were 19A (21.7%), 11A (17.4%), and 15A (17.4%). Erythromycin, clindamycin, tetracycline, trimethoprim-sulfamethoxazole, and levofloxacin resistant rates were 30.4%, 15.6%, 16.3%, 16.3%, and 1.5%, respectively. CONCLUSION: Although pneumococcal disease continues to be a health burden in adults in Crete, our study reveals a herd protection effect of the infant pneumococcal higher-valent conjugate vaccination. Surveillance of changes in serotype distribution and antimicrobial resistance among pneumococcal isolates are necessary to guide optimal prevention and treatment strategies.