Streptococcus pneumoniae serotypes/serogroups causing invasive disease in Riyadh, Saudi Arabia: extent of coverage by pneumococcal vaccines.

Background: Serogroup distribution of sterile site pneumococcal isolates varies between developing and developed countries as well as between different geographical regions. The potential efficacy of any pneumococcal vaccine depends on the degree of representation of the prevalent serogroups in the vaccine. We conducted this study to determine the prevalent pneumococcal serogroups causing invasive infections in Riyadh, Saudi Arabia and to estimate the coverage by the various pneumococcal conjugate vaccines.

Methods: S. pneumoniae isolated between February 2000 and November 2001 from sterile sites of patients of all age groups were collected from 8 major hospitals in Riyadh and serogrouped using the latex agglutination method.

Results: Isolates from 78 patients, 72% of whom were children, were studied. Eighty-eight percent of the isolates belonged to only 10 serogroups/serotypes, namely 6 and 19, 1 and 15, 14 and 23, 7, 18 and 22, in descending order of frequency. Potential coverage of the 7-valent, 9-valent, and 11-valent conjugate vaccines were 54%, 65% and 73%, respectively. The rate of reduced penicillin susceptibility in the serogroups represented in the 7-valent conjugate vaccine was significantly higher than in the non-vaccine serogroups (62% vs. 25%; P=0.0023).

Conclusion: The currently available 7-valent pneumococcal conjugate vaccine provides sub-optimal coverage to serogroups causing invasive diseases in our community. However, this vaccine would be a useful adjunct to penicillin prophylaxis in at-risk patients in the community. The effectiveness of the vaccine would be greater if serotype 15 could be included.