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CDC’s Role in Tracking Trends in Resistance

NARMS Surveillance and Laboratory Testing

CDC, through NARMS, tracks antibiotic resistance and studies patterns of emerging resistance in select bacteria transmitted commonly through food. Surveillance helps identify patterns of emerging resistance that can guide public health prevention and policy efforts to protect people from resistant infections. This information is used by a variety of stakeholders, including federal regulatory agencies, policymakers, consumer advocacy groups, industry, and the public.

National surveillance for NARMS is in all 50 states with several large metropolitan areas participating independently (New York City, Los Angeles, Houston, and Washington, D.C.)

Laboratory Testing and Isolate Submissions
The CDC reference laboratory conducts antibiotic susceptibility testing on isolates from sporadic cases and outbreaks of illness. The lab also confirms and studies bacteria that have new antibiotic resistance patterns and performs research to understand the genetic mechanisms of resistance and how they are spread.

Sporadic Infections
Public health laboratories submit every 20th non-typhoidal Salmonella, Shigella, and Escherichia coli O157 isolate received at their laboratories to CDC NARMS for antibiotic susceptibility testing. They also submit every Salmonella serotype Typhi, serotype Paratyphi A, serotype Paratyphi C, and Vibrio (other than V. cholerae) isolate received at their laboratories.

Public health laboratories of the 10 state health departments that participate in CDC’s Foodborne Diseases Active Surveillance Network (FoodNet) also forward a sample of Campylobacter isolates to CDC for susceptibility testing. The FoodNet sites are Connecticut, Georgia, Maryland, Minnesota, New Mexico, Oregon, Tennessee, and selected counties in California, Colorado, and New York.

Pathogen tested Year testing began Current sampling scheme
Salmonella, non-Typhi 1996 1 in 20
E. coli O157 1996 1 in 20
Shigella 1999 1 in 20
Campylobacter 1997 varies
Salmonella Typhi 1999 all
Salmonella Paratyphi A and C 2008 all
Vibrio species other than V. cholerae 2009 all

Outbreak Investigations
CDC NARMS tests bacteria from outbreaks for antibiotic resistance. Resistance patterns and mechanisms can help investigators identify the source of an outbreak or provide clues about the source of the outbreak. Outbreaks in 2011, 2011-2012, and 2013 of multi-resistant Salmonella traced to ground beef and poultry show how animal and human health are linked.

Antibiotics Tested by NARMS
NARMS tests isolates to determine their antibiotic susceptibility. This is accomplished by determining the lowest concentration of a particular antibiotic that will inhibit the growth of the bacteria. This is called the minimum inhibitory concentration (MIC).  CDC NARMS tests for susceptibility to 22 antibiotic agents that are in 13 classes of drugs.

The names and classes of drugs and the testing methods used for susceptibility testing depend on the type of bacteria being tested. For more details on antibiotics tested, refer to Tables 2 [PDF - 71 pages], 3 [PDF - 71 pages], and 4 [PDF - 71 pages] in the NARMS 2011 Human Isolates Annual Report [PDF - 71 pages]

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