ATLANTA—Multidrug-resistant Streptococcus pneumoniae strains are becoming increasingly common. A study from the Centers for Disease Control and Prevention (CDC) found that 14% of S pneumoniae isolates available for testing in the United States in 1998 were resistant to at least three classes of antimicrobials, up from 9% in 1995.[1] Six serotypes accounted for 90% of the resistant isolates.

“Multidrug resistance can make it hard to treat an infectious organism,” said Anne Schuchat, MD, in an interview with PULMONARY REVIEWS. Therefore, disease prevention should be a priority, she said. Dr. Schuchat, a study author and Chief of the Respiratory Diseases Branch at the National Center for Infectious Diseases in Atlanta, recommends increased immunization with the 23-valent pneumococcal polysaccharide and 7-valent conjugate vaccines, since most of the penicillin-resistant isolates detected in the study were of the serotypes included in these vaccines.

More than 12,000 S pneumoniae isolates were collected during the study’s surveillance period, which lasted from 1995 to 1998. They underwent susceptibility testing with 15 antimicrobial agents.

In 1998, 4,013 cases of invasive pneumococcal infection were reported to the CDC (cumulative incidence, 23 cases per 100,000 population). S pneumoniae isolates were available for 3,475 of these cases, and the isolates almost always came from blood. More than one third of isolates were resistant to at least one antimicrobial agent; the rest were susceptible to all the agents tested.

Trimethoprim-sulfamethoxazole (TMP-SMX) resistance was seen most frequently, occurring in 29% of the isolates. Rifampin, quinupristin-dalfopristin, and levofloxacin resistance were least common, appearing in 1% or less. All isolates were susceptible to vancomycin, known for its increasing ineffectiveness against enterococci. Twenty-four percent of isolates were penicillin resistant. These isolates were far more likely than penicillin-susceptible ones to display high levels of multidrug resistance. A similar pattern arose for S pneumoniae isolates resistant to erythromycin, TMP-SMX, tetracycline, chloramphenicol, clindamycin, levofloxacin, trovafloxacin, or quinupristin-dalfopristin.

Between 1995 and 1998, the percentages of S pneumoniae isolates that were resistant to specific antibiotics (eg, penicillin, meropenem, erythromycin, or TMP-SMX) all rose. Of note, the increases in resistance to nonpenicillin antibiotics occurred only among penicillin-resistant isolates.

“We cannot count on drug companies to create new antibiotics more quickly than pneumococci and other bacteria become resistant,” said Dr. Schuchat. She urged preventive measures against multidrug-resistant S pneumoniae, particularly vaccination and judicious antibiotic use.

--Timothy Begany

Reference
1. Whitney CG, Farley MM, Hadler J, et al. Increasing prevalence of multidrug-resistant Streptococcus pneumoniae in the United States. N Engl J Med. 2000;343:1917-1924.

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