September 16, 2016
2 min read

Resistant nontyphoidal Salmonella more prevalent in blood than stool

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More than 25% of all blood samples collected from nontyphoidal Salmonella patients from 2003 to 2013 were antibiotic resistant, as opposed to approximately 20% of specimens tested from stool, according to a recently published study.

These resistance rates are increasing with times, and frequently confer protection from first-line treatments for Salmonella bacteremia, according to Kristina M. Angelo, DO, MPH-TM, and colleagues.

“Resistance to first-line treatment agents in patients with Salmonella bacteremia is a concern for public health and clinical outcomes and is important for informing clinical decisions regarding appropriate treatment,” they wrote. “If this path of increasing resistance continues, we may soon be at a crossroads where first-line treatment recommendations will need to change, as occurred with gonorrhea treatment and the use of cefixime.”

Angelo and colleagues reviewed test data of Salmonella isolates submitted to the CDC’s National Antimicrobial Resistance Monitoring System (NARMS) from 2003 to 2013. They limited their analysis to isolates from blood or stool, and excluded all serotypes responsible for typhoidal illness. Along with recording drug resistance rates for both sample types, the researchers analyzed their findings to identify trends in donor characteristics and Salmonella serotypes during the study period.


This colorized scanning electron micrograph depicts a colony of Salmonella Typhimurium bacteria.

Source: Janice Haney Carr/CDC

Angelo and colleagues included 20,866 isolates in their final analysis; 94.3% of these were from stool, and the remainder was collected from blood samples. While men and women submitted approximately the same proportion of Salmonella isolates, men were more likely to have bacteremia than women (OR = 1.23; 95% CI, 1.09-1.39). The median age of patients with bacteremia was greater than that of patients with stool (P < .0001), with patients aged at least 65 years were at greater risk for bacteremia than those aged 18 to 64 years. Serotypes most frequently detected in bacteremia cases included Dublin (OR = 128.2; 95% CI, 57.19-287.4), Sandiego (OR = 4.9; 95% CI, 2.9-8.29) and Schwarzengrund (OR = 3.44; 95% CI, 2.14-5.55).

Twenty-seven percent of blood isolates were resistant to at least one agent, as opposed to 20.4% of isolates from stool. Blood isolates were generally associated with greater rates of drug resistance than stool isolates, with 73% of blood isolates resistant to at least one first-line treatment agent. Serotypes Panama (OR = 6.85; 95% CI, 1.25-37.58), Javiana (OR = 3.76; 95% CI, 1.08-13.04), Typhimurium (OR = 2.04; 95% CI, 1.52-2.73) and Enteritidis (OR = 1.61; 95% CI, 1.13-2.29) were associated with greater rates of resistance when detected in blood. Stool samples of the serotype I 4,[5],12i:– were also more likely to demonstrate resistance.

During the study period, ciprofloxacin resistance rates increased among stool isolates, while those for ampicillin and ceftriaxone decreased; however, ceftriaxone resistance increased in bacteremia cases (OR = 1.12; 95% CI, 1.02-1.22). Resistance to TMP-SMX did not change for either sample type.

When comparing these findings with a previous NARMS-based study, the researchers found resistance to certain drugs, such as ceftriaxone or fluoroquinolones, have greatly increased during the study period.

“Judicious antimicrobial use in both humans and food-producing animals is crucial to limit the emergence and spread of resistance,” the researchers wrote. – by Dave Muoio

Disclosure: The researchers report no relevant financial disclosures.