The Changing Picture of Streptococcus Pneumoniae

Increased use of pneumococcal vaccines generally leads to a reduction in the prevalence of drug-resistant pneumococcal strains, a study finds.

The urgency associated with addressing Streptococcus pneumoniae has only increased with the appearance of antibiotic-resistant strains. An effective approach will require a multi-pronged strategy, including national immunization programs, antibiotic control programs, and ongoing surveillance.

A review published online on February 10, 2012, in Vaccine examined the relationship between antibiotic resistance and S. pneumoniae serotypes, with an emphasis on studies published after the introduction of pneumococcal vaccines. (Since these vaccines have become available and uptake has increased, most countries have reported a decrease in both antibiotic use and antibiotic-resistant S. pneumoniae.)

The researchers’ findings demonstrate how introduction of a vaccine changes the clinical picture of disease:

• Prevalence rates of penicillin non-susceptible pneumococci have declined in areas where national immunization programs include pneumococcal vaccines.
• Prevalence rates of erythromycin non-susceptible pneumococci initially declined after pneumococcal vaccines became available, but rates have recently begun to increase.
• Fluoroquinolone resistance has remained low (under 5%), except in areas where these antibiotics were used widely in institutional settings during outbreaks, or in children previously treated with fluoroquinolones.
• Promotion of pneumococcal vaccines through national immunization programs was followed by declines in the prevalence of pneumococcal multidrug resistance (MDR; usually defined as resistance to 3 or more drugs). From 1999 to 2004 in the United States, the overall rate of invasive MDR isolates declined by 59% among all age groups and by 84% among children aged 2 years or younger.
• Emergence of MDR clones, particularly serotype 19A, is of great concern because of its potential for invasiveness and its ability to become MDR quickly.

The authors note that vaccines that protect against more serotypes—particularly the more virulent serotypes—are advantageous. In the future, a vaccine that is protein-specific rather than serotype-specific might eliminate the need to vaccinate against specific serotypes.

Ms. Wick is a visiting professor at the University of Connecticut School of Pharmacy and a freelance writer from Virginia.