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NARMS 2015 Human Isolates Surveillance Report

CDC NARMS tracks antimicrobial resistance in Salmonella and other intestinal (enteric) bacteria that may cause mild or severe diarrhea or bloodstream infection. NARMS is an interagency partnership among the U.S. Centers for Disease Control and Prevention (CDC), the U.S. Food and Drug Administration (FDA), the U.S. Department of Agriculture (USDA), and state and local health departments.

Bacterial foodborne infections are common and can sometimes be serious. In severe cases, the right antibiotic, also called antimicrobial agent, can be life-saving. Some antibiotics don’t work because the foodborne pathogen has become resistant.  NARMS is the only source of national information on antibiotic resistance in foodborne pathogens like Salmonella. Understanding trends in antibiotic resistance helps doctors to prescribe effective treatment and public health officials to investigate outbreaks faster.

Report cover for NARMS 2015 Human Isolates Surveillance Report

The NARMS 2015 Human Isolates Report [PDF – 7 MB] provides the most recent nationwide data on antibiotic resistance transmitted commonly by food, including:

  • Salmonella
  • Shigella
  • Campylobacter
  • E. coli O157
  • Vibrio species other than Vibrio cholerae

Report Highlights

Whole Genome Sequencing of Salmonella

For this report, NARMS conducted whole genome sequencing (WGS) of all nontyphoidal Salmonella collected in 2015, regardless of phenotypic resistance. Genetic data provided by this sequencing can be used to identify resistance genes and predict antimicrobial resistance.

Key Trends

To determine trends, NARMS compared the prevalence of antibiotic resistance in 2015 with the average prevalence from two reference periods: 2004–2008 and the previous five years, 2010–2014. The 2004–2008 reference period begins with the second year that all 50 states participated in Salmonella and Shigella surveillance and all 10 FoodNet sites participated in NARMS Campylobacter surveillance. The additional 2010–2014 reference period allows comparison with more recent years. Some trends were encouraging; others were concerning.


  • Resistance to ceftriaxone in Salmonella remained rare, but notable:
    • 2015: 2.7%
    • 2004–2008 and 2009-2013: 3.2% and 2.6%, respectively
  • Multidrug resistance to certain groups of antibiotics in Salmonella Typhimurium (ACSSuT) and Salmonella Newport (ACSSuTAuCx) were lower or remained stable in 2015 compared with 2004–2008 and 2010–2014.
  • Salmonella isolates did not have a combination of resistance to ceftriaxone and decreased susceptibility to azithromycin; these are important drugs for the treatment of severe Salmonella infections.


  • Multidrug resistance (ASSuT) in a common Salmonella serotype (l 4,[5],12:i:-) was nearly 60%.
    • This resistance more than tripled since 2011 (18% in 2011 vs. 59% in 2015) and has been linked to eating pork, beef, and to animal exposure.
  • Eight of the 65 ceftriaxone-resistant Salmonella in 2015 had an extended-spectrum β-lactamase (ESBL) gene identified by WGS.
    • ESBLs are rare among Salmonella in the United States. Many of these infections are acquired during international travel.
  • Salmonella serotypes Dublin, Heidelberg, Infantis, I 4,[5],12:i:-, Newport, and Typhimurium accounted for nearly three quarters of isolates that were resistant to ceftriaxone.
    • 67% of serotype Dublin isolates were resistant to ceftriaxone.
  • Decreased susceptibility to ciprofloxacin in Salmonella was higher in 2015 (5.8%) than in the reference periods of 2004–2008 (2.4%) and 20102014 (3.4%).
    • 14% of Salmonella Enteritidis (the most common Salmonella serotype) had decreased susceptibility to ciprofloxacin, up from 8% the previous year.
  • Eight Salmonella isolates had decreased susceptibility to azithromycin in 2015, the most since testing began in 2011.
    • Five of these eight isolates also had decreased susceptibility to ciprofloxacin.
  • Decreased susceptibility to ciprofloxacin among Salmonella Typhi remained high at 66%.
  • Campylobacter resistance to fluoroquinolones remained high, at times leaving macrolides as the only treatment option.
    • Ciprofloxacin resistance in Campylobacter jejuni, the most common species isolated from humans, remained over 25% in 2015. Resistance in Campylobacter coli increased from 35% in 2014 to 40% in 2015. Resistance in 2015 for both C. jejuni and C. coli were significantly higher than the reference period of 20102014 (21% and 28%, respectively).
    • Macrolide resistance in 2015 for Campylobacter jejuni (2.7%) and Campylobacter coli (13%) were higher than in 2014 (1.8% and 10%, respectively).
  • Decreased susceptibility to ciprofloxacin among Shigella was higher in 2015 (9.8%) than in the reference periods of 2004–2008 (1.7%) and in 20102014 (5.8%).
  • Decreased susceptibility to azithromycin among Shigella increased from 4.7% in 2014 to 9.8% in 2015.
    • Among Shigella sonnei, the increase was from 2.0% in 2014 to 6.1% in 2015.
    • Among Shigella flexneri, the increase was from 22% in 2014 to 33% in 2015.

Further Reading - Healthy People 2020 Progress Report

Learn how 2015 data were used to assess progress towards the Healthy People 2020 food safety topic area objectives related to antibiotic resistance in nontyphoidal Salmonella and Campylobacter jejuni isolates from humans. Read the progress report >