Emerging resistant serotypes of invasive Streptococcus pneumoniae Sittana Elshafie,1,2 Saad J Taj-Aldeen2,3 1Qatar Orthopedic and Sports Medicine Hospital, Aspetar, Doha, Qatar; 2Weill Cornell Medicine-Qatar, 3Department of Laboratory Medicine and Pathology, Microbiology Division, Hamad Medical Corporation, Doha, Qatar Background: Streptococcus pneumoniae is the leading cause of meningitis and sepsis. The aim of the study was to analyze the distribution, vaccine serotype coverage, and antibiotic resistance of S. pneumoniae serotypes isolated from patients with invasive diseases, after the introduction of pneumococcal 7-valent conjugated vaccine (PCV-7). Methods: A total of 134 isolates were collected from blood and cerebrospinal fluid specimens at Hamad Hospital during the period from 2005 to 2009. Isolate serotyping was done using the Quellung reaction. The prevaccination period was considered before 2005. Results: The most common serotypes for all age groups were 3 (12.70%), 14 (11.90%), 1 (11.90%), 19A (9.00%), 9V (5.20%), 23F (5.20%), and 19F (4.50%). Coverage rates for infant <2 years for PCV-7, the 10-valent conjugated vaccine (PCV-10), and the 13-valent conjugated vaccine (PCV-13) were 34.78%, 52.17%, and 78.26%, respectively. Coverage rates of these vaccines were 50%, 67.86%, and 75% for the 2–5 years age group; 27.12%, 40.68%, and 64.41% for the age group 6–64 years; and 25%, 33.33%, and 66.67% for the ≥65 years age group, respectively. The percentage of nonsusceptible isolates to penicillin, cefotaxime, and erythromycin were 43.86%, 16.66%, and 22.81%, respectively. Thirty-seven isolates (32.46%) were multidrug resistant (MDR) and belonged to serotypes 14, 19A, 19F, 23F, 1, 9V, 12F, 4, 6B, 3, and 15A. Compared to previous results before the introduction of PCV-7, there was a significant reduction in penicillin-nonsusceptable S. pneumoniae from 66.67% to 43.86%, and a slight insignificant reduction in erythromycin nonsusceptible strains from 27.60% to 22.8%, while there was a significant increase in cefotaxime nonsusceptible strains from 3.55% to 16.66%. Conclusion: Invasive pneumococcal strains and the emergence of MDR serotypes is a global burden that must be addressed through multiple strategies, including vaccination, antibiotic stewardship, and continuous surveillance. Keywords: Streptococcus pneumoniae, Qatar, vaccine, serotype distribution, antibiotic resistance