BETHESDA, MD. — The percentage of nalidixic acid-resistant Salmonella enteritidis isolates increased significantly, from 1% to 5%, between 1996 and 2003, Felicita Medalla, M.D., said at an annual conference on antimicrobial resistance sponsored by the National Foundation for Infectious Diseases.
Participating state health departments have submitted Salmonella isolates to the National Antimicrobial Resistance Monitoring System (NARMS) since 1996. Between 1996 and 2003, 2,349 Salmonella enteritidis isolates were tested, and 64 (3%) were resistant to the antimicrobial agent nalidixic acid, noted Dr. Medalla, a member of the NARMS working group at the Centers for Disease Control and Prevention in Atlanta.
Salmonella enteritidis was the second most common serotype reported in laboratory-confirmed cases in 2003, Dr. Medalla reported.
Most Salmonella infections stem from the consumption of eggs, chicken, and egg-containing foods. The illness causes symptoms similar to gastroenteritis and usually does not require treatment. However, when treatment is needed, resistance is a concern. Quinolones have been the mainstay treatment, and nalidixic acid resistance in Salmonella has been associated with decreased susceptibility to quinolones such as ciprofloxacin in previous studies. Overall, 88% of the nalidixic acid-resistant S. enteritidis isolates from the 1996–2003 NARMS data sets showed decreased susceptibility to ciprofloxacin.
Resistance to nalidixic acid in any non-typhi Salmonella increased significantly during the study, from 5 of 1,326 isolates in 1996 (0.4%) to 47 of 1,873 isolates in 2003 (3%).
Whether the nalidixic acid-resistant Salmonella infections were acquired internationally or domestically remains to be studied, Dr. Medalla said, but clinical monitoring of resistance is important, given the public health implications.