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By Emma Hitt, PhD

ATLANTA (Reuters Health) – Streptococcus pneumoniae resistance to fluoroquinolones is an emerging problem in the US, according to the Centers for Disease Control and Prevention, and physicians are being urged to use these antibiotics appropriately.

Older fluoroquinolones include ofloxacin and ciprofloxacin, and newer fluoroquinolones with higher in vitro activity against S. pneumoniae include levofloxacin, grepafloxacin, gatifloxacin, and moxifloxacin, CDC researchers note in the September 21st issue of Morbidity and Mortality Weekly Report.

The CDC's Active Bacterial Core Surveillance determined trends of pneumococcal resistance to fluoroquinolones from 1995 to 1999 in counties of seven states. From 1995 to 1997, they tested 8763 isolates from persons with pneumococcal invasive disease for susceptibility to ofloxacin. Then from 1998 to 1999, they tested 6529 isolates for susceptibility to levofloxacin.

The prevalence of ofloxacin-nonsusceptible isolates increased from 3.1% in 1995 to 4.5% in 1997 and was higher among adults than among children younger than 18 years, for whom fluoroquinolone use is not licensed. All levofloxacin-nonsusceptible isolates were found in adults and the prevalence increased only slightly, from 0.2% in 1998 to 0.3% in 1999.

"It is unclear whether resistance is increasing with the newer fluoroquinolones," the CDC researchers write, adding that "trends in ofloxacin susceptibility may predict what will occur for other fluoroquinolone agents."

Fluoroquinolone resistance was associated with resistance to other classes of antimicrobials. Of the 15 isolates that were nonsusceptible to levofloxacin, many showed decreased susceptibility to penicillin, cefotaxime, erythromycin, and/or trimethoprim-sulfamethoxazole.

According to the CDC, fluoroquinolones are being prescribed with increasing frequency and this may contribute to the emergence of fluoroquinolone-resistant pneumococci. From 1993 to 1998, fluoroquinolone prescriptions in the US increased from 3.1 to 4.6 per 100 persons per year, with the number highest among persons 65 years of age or older.

"Although fluoroquinolone resistance is still limited, we have seen an increase that may be related to antibiotic use, which is new in this country," Dr. Montse Soriano-Gabarro, with the CDC's National Center for Infectious Diseases, told Reuters Health.

"It is hard to say whether resistance will increase, but resistance to fluoroquinolones is linked to antimicrobial use, and resistance will likely increase as use increases," Dr. Soriano-Gabarro said. "We need to be judicious in the use of fluoroquinolones."

MMWR 2001;50:800-804.