Nalidixic acid-resistant Salmonella tied to international travel
A high percentage of nalidixic acid-resistant Salmonella serotype Enteritidis infections are linked to recent travel outside of the United States, according to recent findings.
In the study, researchers collected data from the National Antimicrobial Resistance Monitoring System (NARMS), a joint effort by the CDC, FDA, US Department of Agriculture and other health agencies to surveil antimicrobial resistance among enteric bacteria in humans, retail meat and food animals. NARMS collects human isolates of nontyphoidal Salmonella and other enteric pathogens and tests their vulnerability to a variety of antimicrobial agents.
Isolates of Salmonella serotype Enteritidis (SE) were collected for 368 patients, and interpretive criteria from the CDC NARMS Annual Report were applied to test resistance to the following: amikacin, ampicillin, amoxicillin-clavulanic acid, cefoxitin, ceftiofur, ceftriaxone, chloramphenicol, ciprofloxacin, gentamicin, kanamycin, nalidixic acid (NA), streptomycin, sulfisoxazole, tetracycline and trimethoprim-sulfamethoxazole.
The researchers linked the NARMS data on the isolates to data from FoodNet, a multi-agency collaboration that conducts surveillance for infections from nine food-transmitted pathogens. The data collected from this resource included history of travel outside the United States within 7 days of illness onset. The researchers compared patients with NA-resistant isolates (n=28) to those with NA-susceptible isolates (n=340), specifically in terms of recent international travel history. The percentage of isolates from individuals who had traveled outside the United States was calculated for both groups, and results were compared.
The researchers found that 75 (20%) of the 368 S. enterica patients reported a history of travel outside the United States before the onset of infection. Of the total SE patient population, 28 had isolates showing resistance to NA, and 18 (64%) were seen in patients with international travel before illness onset. Of the 28 NA-resistant isolates, 24 (86%) demonstrated lowered susceptibility to ciprofloxacin (minimum inhibitory concentrations ≥0.12 mcg/mL), one isolate was ciprofloxacin-resistant (MIC ≥1 mcg/mL) and 23 demonstrated moderate ciprofloxacin MICs (0.12 mcg/mL-0.5 mcg/mL). Of the NA-resistant isolates seen in patients with recent international travel history, all 18 had intermediate ciprofloxacin MICs. Of patients with international travel history, 24% had NA-resistant SE infection vs. 3% of patients who did not travel.
Although the researchers noted that these findings provided key information about the link between NA-resistant SE infection and international travel, they added that little is known about the source of infection among NA-resistant SE in patients who did not report travel within 7 days of infection.
“This analysis provides important information regarding sources of NA-resistant SE that may provide a better understanding of the diversity of sources and transmission pathways of salmonellosis,” the researchers wrote. “Additional research is needed to ascertain travel destinations and exposure sources associated with NA-resistant SE infections acquired during international travel, to identify sources of domestically acquired NA-resistant SE infections, and to examine clinical outcomes of NA-resistant infections.”
Disclosure: The researchers report no relevant financial disclosures.