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Highly Drug-Resistant Non-Typhoidal Salmonella in the United States, 1996–2012 Open Access

Background. Non-typhoidal Salmonella(NTS) causes an estimated 1.2 million illnesses, 23,000 hospitalizations, and 450 deaths in the United States each year. While not indicated for most infections, antimicrobial treatment is critical for severe salmonellosis. We describe the epidemiology of the most highly drug-resistant NTS detected by the National Antimicrobial Resistance Monitoring System (NARMS).

Methods. Participating health departments submitted every 10^th (1996–2002) or 20^th(2003–2012) NTS isolate from humans to the NARMS program at CDC, as well as patient demographic and laboratory information. We tested for susceptibility to 14 antimicrobial agents in 8 classes. We defined isolates as ‘highly drug-resistant’ (HDR) if they were non-susceptible to ≥7 antimicrobial classes or ≥3 of 4 clinically important agents: ceftriaxone, ciprofloxacin, ampicillin, trimethoprim-sulfamethoxazole. We calculated odds ratios (OR) and 95% exact confidence intervals (CI) for categorical variables comparing HDR infections to those susceptible to all agents.

Results. During 1996–2012, 2.2% (689/31,931) of NTS isolates were HDR (627 were non-susceptible to ≥7 antimicrobial classes, and 202 were non-susceptible to ≥3 clinically important agents; 140 met both HDR criteria). The HDR proportion increased from 0% in 1996 to 2.2% in 2012, peaking at 3.6% in 2003. HDR isolates included 43 serotypes, most commonly Newport (54.4%), Typhimurium (23.8%), Agona (3.6%) and Dublin (3.3%). Among pansusceptible isolates (n = 25,083), the most common serotypes were Enteritidis (20.5%), Typhimurium (14.0%), Newport (10.6%), and Javiana (5.7%). HDR infections were associated with patient age ≥18 years (OR = 1.4, 95% CI = 1.2–1.7) and residence in a US region other than the South (OR = 4.1, 95% CI = 3.2–5.3).

Conclusion. Infections with HDR Salmonella emerged and persisted during 1996–2012. These infections were most common in adult patients and least common in the South. Four serotypes, all of which commonly display resistance in food animals, accounted for 85% of the infections. As treatment options for these infections are limited, prudent use of clinically important antimicrobial agents in both humans and animals is crucial to preserve their effectiveness.

Disclosures. All authors: No reported disclosures.

Author notes