Pneumococcal bacteremia among infants with fever without known source before and after introduction of pneumococcal conjugate vaccine in the Basque Country of Spain.

BACKGROUND

The introduction of vaccination with the heptavalent pneumococcal conjugate vaccine (PCV7) has produced an important decrease in the incidence of Streptococcus pneumoniae occult bacteremia (OB). In Spain, PCV7 became available in the last months of 2001, but, to date, it has not been included in the official vaccination schedule of the public health system.

OBJECTIVE

To describe the impact of pneumococcal vaccination with PCV7 on the incidence of OB caused by S. pneumoniae in infants aged 3-36 months presenting to our pediatric emergency department.

METHODS

This is a retrospective case series of all blood cultures obtained from January 1, 2000 to December 31, 2005 in our pediatric emergency department from infants with fever without known source. We evaluated rates of blood cultures positive with S. pneumoniae before (January 1, 2000-December 31, 2001) and after (January 1, 2004-December 31, 2005) PCV7 introduction, excluding 2 transitional years (January 1, 2002-December 31, 2003).

RESULTS

Implementation of vaccination with PVC7 in our area resulted in a 57.5% reduction of OB caused by S. pneumoniae (1.62-0.69%) (P < 0.05). There were 30 cases of bacteremia caused by S. pneumoniae, 19 before and 11 after PCV7 introduction. Between the 2 periods of time studied the number of cases of infants aged 3-36 months with fever without known source, increased from 8052 to 9799 (21.6%) and the total blood cultures drawn significantly increased from 1171 to 1575 (34.5%) (P < 0.01). Despite more frequent blood culturing in febrile patients, the rate of OB caused by PCV7-serotypes decreased significantly by 79% (1.19-0.25%) (P < 0.01) and the proportion of OB caused by nonvaccine serotypes increased minimally from 0.42 to 0.44%. In the post-PVC7 period, 4 infants presented with S. pneumoniae OB caused by PCV7 serotypes; 2 had not received PCV7, and 2 (6 and 7 months old) had received one dose.

CONCLUSIONS

After PCV7 introduction in our area, rates of S. pneumoniae OB caused by vaccine serotypes decreased significantly despite only moderate use of the vaccine in our population.