ATLANTA—More strains of Streptococcus pneumoniae now show resistance to fluoroquinolones, the Centers for Disease Control and Prevention (CDC) recently reported.

A new analysis of data showed that the overall prevalence of ofloxacin resistance in this country rose from 2.6% of all isolates in 1995 to 3.8% in 1997. Levofloxacin resistance was found in 0.2% of pneumococcal isolates in 1998 and 1999.[1] “Although this trend is not alarming right now, it does require careful study,” Chris Van Beneden, MD, told PULMONARY REVIEWS. Dr. Van Beneden is a Medical Epidemiologist in the Respiratory Diseases Branch at the CDC.

LARGE NATIONAL DATA SOURCES

To gauge pneumococcal resistance to fluoroquinolones, the CDC analyzed prevalence data on invasive pneumococcal disease that had been collected by the Active Bacterial Core Surveillance (ABCs) system from 1995 to 1999. The ABCs system performed surveillance for invasive bacterial infections in seven states with a total population of 17.3 million.

Pneumococcal isolates were tested for susceptibility to ofloxacin from 1995 through 1997 and to levofloxacin and trovafloxacin in 1998 and 1999. For all of these drugs, nonsusceptibility was defined as a minimum inhibitory concentration of 4 µg/mL or greater.

Fluoroquinolone prescription data for 1993 to 1998 were obtained from the National Hospital Ambulatory Medical Care Survey. This ongoing survey collects data on ambulatory care services use in hospital emergency and outpatient departments for a representative national sample.

CDC URGES APPROPRIATE USE

From 1995 through 1997, susceptibility testing was available for 8,763 cases of invasive pneumococcal disease. In all three years, isolates not susceptible to ofloxacin were more than twice as common in adults as in children. Among adults, 4.5% of all pneumococcal isolates were not susceptible to ofloxacin by 1997.

A total of 6,529 cases were available for analysis in 1998 and 1999. In 15 cases, pneumococcal isolates were not susceptible to levofloxacin; in 13 of these cases, the isolates were also not susceptible to trovafloxacin. All 15 cases occurred in adults.

Isolates not susceptible to levofloxacin were significantly more common in white patients and in those 65 years or older. Resistance to levofloxacin and trovafloxacin was linked with resistance to other antimicrobials, including penicillin, cefotaxime, erythromycin, and trimethoprim-sulfamethoxazole.

From 1993 to 1998, fluoroquinolone prescriptions in the United States rose from 3.1 to 4.6 per 100 persons annually, the CDC also reported. The increase in prescriptions was greatest among those 65 years and older—from 8.2 to 12.4 per 100 persons annually.

Although still rare, fluoroquinolone-resistant pneumococci may continue to increase in prevalence with fluoroquinolone use, the CDC said. It is unclear if the problem is occurring yet with the newer formulations.

Educating practitioners and the public about appropriate fluoroquinolone use is crucial for slowing the rise in pneumococci resistant to these drugs, Dr. Van Beneden stressed. Other important measures include continuous prospective surveillance, routine susceptibility testing if resistance becomes more common, and reporting to state or local health departments suspected cases of fluoroquinolone resistance.

—Timothy Begany

Reference
1. Centers for Disease Control and Prevention. Resistance of Streptococcus pneumoniae to fluoroquinolones—United States, 1995-1999. MMWR Morb Mortal Wkly Rep. 2001;50:800-804.

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