Background: Invasive pneumococcal disease (IPD) continues to be a significant burden in children despite the implementation of two generations of conjugate vaccines. Serotype replacement by nonvaccine serotypes is reported in multiple areas around the world. This study is a continuation of previous studies and describes the incidence, serotype distribution, and antibiotic resistance pattern of Streptococcus pneumoniae serotypes causing IPD at Children's Medical Center Dallas after introduction of 13-valent pneumococcal conjugate vaccine (PCV13).
Methods: Streptococcus pneumoniae isolates from normally sterile sites were collected from January 1, 1999 to June 30, 2014. Demographic and clinical information was extracted for analysis. Incidence of IPD was calculated using inpatient and emergency center admissions to Children's Medical Center of Dallas as the denominator. Isolates were serotyped and penicillin/cefotaxime susceptibilities were determined. Selected nontypeable isolates were further characterized by multilocus sequence typing. A χ2 test and the Cochran-Armitage Trend Test for trend analysis were used to evaluate change in serotype and antibiotic susceptibility patterns over time.
Results: Comparison of the different study periods showed a significant reduction in the incidence of IPD in PCV13 era compared with prevaccine era and PCV7 era (P < .05). Children younger than 24 months showed the largest reduction of disease incidence. More than 40% of patients with IPD had a documented comorbidity. Cases of pneumonia continued to decrease in the PCV13 era (P < .002). The most common non-PCV13 serotypes after vaccine introduction were as follows: 23B, 6C, 23A, 9N/L, and 12. Penicillin resistance by meningitis breakpoint decreased significantly in the PCV13 era.
Conclusions: After introduction of PCV13 in Dallas, incidence of IPD caused by strains contained in the vaccine and penicillin resistance continued to decrease. Serotype replacement phenomena and persistence of PCV7 serotypes were documented. Patients with comorbidities represented a large percentage of patients with IPD. Concerns for geographic variation in serotype replacement phenomena arise from the present study.
Keywords: IPD; Streptococcus pneumoniae; pneumococcal conjugate vaccine; serotype distribution.
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