Treatment of invasive pneumococcal disease caused by infection with Streptococcus pneumoniae (pneumococcus) is complicated by antimicrobial resistance. Although rates of antimicrobial-nonsusceptible invasive pneumococcal disease decreased in the United States after the introduction of heptavalent pneumococcal conjugate vaccine (PCV7; Prevnar) in 2000, there is growing concern about antimicrobial resistance in serotypes not covered by this vaccine.

The Centers for Disease Control and Prevention (CDC) analyzed surveillance data of invasive pneumococcal disease in Massachusetts residents younger than 18 years from 2001 to 2006, and it examined the clinical characteristics of patients with antimicrobial-nonsusceptible, non–PCV7-type disease. Susceptibility to five commonly used antimicrobials (i.e., amoxicillin, penicillin, ceftriaxone [Rocephin], azithromycin [Zithromax], and trimethoprim/sulfamethoxazole [Bactrim, Septra]) was determined. The findings show an increased number of cases of invasive pneumococcal disease caused by serotypes not covered by PCV7 (particularly 19A), and a related increase in antimicrobial resistance among these isolates.

There were 467 cases of invasive pneumococcal disease in children between October 2001 and September 2006. Of 353 isolates (76 percent) available for serotyping, 94 (27 percent) were serotype 19A. This serotype was responsible for 33 cases (41 percent) of invasive pneumococcal disease between 2005 and 2006, compared with six cases (10 percent) between 2001 and 2002 (P < .01). There were no significant changes in the proportions of disease caused by other PCV7 or PCV7-related serotypes or by non-PCV7 serogroups. Overall rates of invasive pneumococcal disease remained stable (15.9 to 18.6 per 100,000 children younger than five years), despite the increased incidence of antimicrobial-nonsusceptible disease. The clinical outcomes for disease caused by nonsusceptible and susceptible S. pneumoniae serotypes were comparable.

The results confirm that although PCV7 is effective in preventing invasive pneumococcal disease, antimicrobial resistance among serotypes not covered by the vaccine is a concern.