BACKGROUND 　Five of seven serotypes in the pneumococcal cinjugate vaccine,introduced for infants in the United States in 2000,are responsible for most penicillin-resistant infections .We examined the effect of this vaccine on invasive disease caused by resistant strains.

METHODS 　We used laboratorybased data from Active Bacterial Core surveillance to measure disease caused by antibiotic -nonsusceptible pneumococci from 1996 through 2004. Cases of invasive disease, defined as disease caused by pneumococci isolated from a normally sterile site ,were identified in eight surveillance areas. Isolates underwent serotyping and susceptibility testing.

RESULTS 　 Rates of invasive disease caused by penicillin-nonsusceptible strains and strains not susceptible to multiple antibiotics peaked in 1999 and decreased by 2004 ,from 6.3 to 2.7 casesper 100,000 (a decline of 57 percent; 95 percent confidence interval, 55 to 58 percent) and from 4.1 to 1.7 cases per 100,000 (a decline of 59 percent; 95 percent confidence interval ,58 to 60 percent), respectively. Among children under two years of age, disease caused by penicillin-nonsusceptible strains decreased from 70.3 to 13.1 cased per 100,000 (a decline of 81 percent; 95 percent confidence interval, 80 to 82 percent). Among persons 65 years of age or older ,disease caused by penicillin-nonsusceptible strains decreased from 16.4 to 8.4 cases per 100,000 (a dicline of 49 percent). Rates of resistant disease caused by vaccine serotypes fell 87 percent. An increase was seen in disease caused by serotype 19A, a serotype not inc luded in the vaccine (from 2.0 to 8.3 per 100,000 among children under two years of age).

CONCLUSIONS 　 The rate of antibiotic-resistat invasive pneumococcal infections decreased in yong children and older persons after the introduction of the conjugate vaccine .There was an increase in infections caused by serotypers not included in vaccine.

(N Engl J Med 2006;354:1455-63.April 6,2006)