In a study published in Emerging Infectious Diseases, Medalla et al utilized Bayesian hierarchical models of culture-confirmed Salmonella infections between 2004 and 2016 from two CDC surveillance systems to estimate changes in the national incidence of resistant nontyphoidal Salmonella infections. They also tested Salmonella isolates collected through the National Antimicrobial Resistance Monitoring System (NARMS).
The researchers indicated that this data would assist public health practitioners in setting targets and priorities for decreasing the number of antimicrobial-resistant Salmonella infections in the U.S. population. While the researchers assessed isolate susceptibility to agents representing eight to nine antibiotic classes, they focused on identifying resistance to ceftriaxone and ampicillin and nonsusceptibility to ciprofloxacin. These are the three agents primarily used to treat severe Salmonella infections.
Extrapolating to the United States population and accounting for unreported infections, they projected a 40% rise in the annual incidence of infections with clinically important resistance (resistance to ampicillin or ceftriaxone or nonsusceptibility to ciprofloxacin) during 2015 and 2016 (≈222,000 infections) compared with 2004 to 2008 (≈159,000 infections).
In an interview, Felicita Medalla, MD, MS, an epidemiologist in the CDC's Division of Foodborne, Waterborne, and Environmental Diseases, explained that the surge translates to nearly 63,000 more resistant infections per year. The researchers found that over the entire study period, states reported 539,862 culture-confirmed Salmonella infections to Laboratory-Based Enteric Disease Surveillance and submitted 28,265 Salmonella isolates to NARMS.
The authors also noted that clinically significant resistance was detected in 3,456 (12.5%) of the 28,265 isolates, with ampicillin-only resistance detected in 6.6%, ciprofloxacin nonsusceptibility in 3%, and ceftriaxone/ampicillin resistance in 3%. Multidrug resistance was detected in 10.3% of isolates, and the five major serotypes accounted for 69% of infections with clinically important resistance and 66% with multidrug resistance. The authors stated that, "The increased incidence of ciprofloxacin-nonsusceptible Salmonella infections during 2015-2016 compared with both 2004-2008 and 2010-2014 is a concerning trend."
Although most Salmonella infections result in self-limited illness, antimicrobial treatment is recommended for patients with severe infection or at high risk for complications. "Prevention measures that can reduce the risk of Salmonella infection include proper hand-washing, safe food handling, avoiding contact with animals more likely to carry the bacteria (e.g., baby chicks, turtles), and practicing safe food and drinking habits when traveling abroad." The authors suggested that further evaluation of changes in resistance incidence could assist in identifying targeted prevention strategies.
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