Serotype prevalence of occult pneumococcal bacteremia

Objective. The licensure and use of a pneumococcal conjugate vaccine that i s immunogenic in children who are younger than 2 years may affect the epide miology of occult bacteremia. This study was conducted to determine the ser otype prevalence of Streptococcus pneumoniae isolates from children with oc cult bacteremia and to document the proportion that would be covered by the recently licensed heptavalent pneumococcal conjugate vaccine. Methods. A cohort of 5901 children who were 2 to 24 months of age and had a temperature of >39.0 degreesC evaluated with a blood culture at an urban t ertiary care children's hospital emergency department was studied to determ ine the prevalence of S pneumoniae serotypes. Patients were excluded if the ir immune system was suppressed, they had a diagnosis of a focal infection, they were evaluated by lumbar puncture, they were admitted to the hospital , or they died during initial evaluation. Blood cultures were inoculated in to pediatric blood culture bottles and processed using an automated carbon dioxide monitoring system. All pneumococcal isolates were serotyped on the basis of capsular swelling with type-specific antisera (Quellung reaction). Results. The study population consisted of 5901 patients. The overall rate of occult bacteremia was 1.9% (95% confidence interval [CI]: 1.5-2.3). S pn eumoniae accounted for 92 of 111 isolates (82.9%; 95% CI: 74.6-89.4) in chi ldren with occult bacteremia. Eight pneumococcal serotypes were represented : 6A (2%), 9V (6%), 19F (6%), 18C (8%), 4 (9%), 6B (13%), 23F (15%), and 14 (42%). Serotypes 14, 6B, and 23F accounted for 69.3% (95% CI: 58.6-78.7) o f typed isolates. In the cohort, 97.7% (95% CI: 92-99.7) of isolated seroty pes are represented in the newly licensed heptavalent pneumococcal conjugat e vaccine. The single isolated serotype that would not have been covered by the currently licensed heptavalent pneumococcal conjugate vaccine was 6A. Conclusions. S pneumoniae accounts for the vast majority of bacterial patho gens in children with occult bacteremia. As indicated by the results of thi s study, the heptavalent pneumococcal conjugate vaccine may prevent the maj ority of occult pneumococcal bacteremia episodes. The 2 cases of bacteremia with a serotype that would not have been included in the vaccine both were due to serotype 6A. It has been noted that there is potential nonvaccine s erotype and subgroup cross-protection (6A from 6B) afforded to children who are immunized with the heptavalent vaccine. The high potential efficacy of the heptavalent pneumococcal conjugate vaccine for strains that cause occu lt bacteremia in our population may have a profound effect on the treatment of children with fever without a source. There has been an alarming and ra pid emergence of antibiotic-resistant pneumococcal strains. Less pressure t o use broad-spectrum antibiotics, which in turn causes further antibiotic r esistance, should result. Laboratory testing and hospitalization also shoul d be reduced. The prevalence rates determined by this study may be used as baseline data for comparison of serotype rates of occult pneumococcal bacte remia after widespread use of the heptavalent vaccine.