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Numerator

Number of non-typhoidal Salmonella isolates that are resistant to gentamicin

Denominator

Number of non- typhoidal Salmonella isolates tested for resistance to gentamicin

Methodology

The primary objectives of NARMS are to:

  1. Monitor trends in antimicrobial resistance among foodborne bacteria from humans, retail meats, and animals
  2. Disseminate timely information on antimicrobial resistance to promote interventions that reduce resistance among foodborne bacteria
  3. Conduct research to better understand the emergence, persistence, and spread of antimicrobial resistance
  4. Assist the FDA in making decisions related to the approval of safe and effective antimicrobial drugs for animals

In 1996, surveillance for Salmonella in NARMS began in 14 sites. Since 2003, all 50 states have been participating, which represent a population of approximately 308 million (US census, 2010). Participating sites forward every Salmonella Typhi isolate, every twentieth non-typhoidal Salmonella, every twentieth Shigella isolate, and every twentieth E. coli O157 isolate received at their public health laboratories to NARMS at CDC for susceptibility testing.

Susceptibility testing involves determination of minimum inhibitory concentrations for 15 antimicrobial agents: amikacin, ampicillin, amoxicillin-clavulanic acid, cefoxitin, ceftiofur, ceftriaxone, chloramphenicol, ciprofloxacin, gentamicin, kanamycin, nalidixic acid, streptomycin, sulfisoxazole, tetracycline, and trimethoprim-sulfamethoxazole. Resistance in non-typhoidal Salmonella is used for this objective. Non-typhoidal Salmonella excludes the following Salmonella serotypes: Typhi, Paratyphi A, Paratyphi B (i.e., tartrate negative isolates), and Paratyphi C. Tartrate positive Salmonella serotype Paratyphi B isolates are referred to as Salmonella serotype Paratyphi B var. L(+) tartrate+ and are not typically associated with typhoidal disease.

The FoodNet sites (California, Colorado, Connecticut, Georgia, Maryland, Minnesota, New York, New Mexico, Oregon and Tennessee) also send one Campylobacter isolate each week to CDC. Susceptibility testing of Campylobacter is performed to determine the MICs for eight antimicrobial agents: azithromycin, chloramphenicol, ciprofloxacin, clindamycin, erythromycin, gentamicin, nalidixic acid and tetracycline.