September 06, 2016
2 min read

MSM face elevated risk for drug-resistant shigellosis

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Men who have sex with men appear to be at greater risk for transmitting drug-resistant strains of shigellosis, according to an analysis of transmission route and antimicrobial resistance among shigellosis clusters reported in the United States from 2011 to 2015.

“All shigellosis clusters that we identified among MSM in the United States during 2011-2015 were caused by strains resistant to one or more of the preferred antimicrobial agents for shigellosis,” Anna Bowen, MD, MPH, medical epidemiologist at the CDC, and colleagues wrote in Emerging Infectious Diseases. “Although our sample was small, the estimated prevalence of resistance to preferred antimicrobial drugs for MSM-associated shigellosis clusters was three to 77 times the prevalence for clusters with nonsexual transmission routes.”

Strains of shigellosis resistant to the preferred antimicrobial agents — ciprofloxacin, ceftriaxone and azithromycin — have emerged in the U.S. and abroad, but estimates of risk among different populations or by transmission route were unknown. Thus, Bowen, along with fellow CDC epidemiologist Robert D. Kirkcaldy, MD, MPH, and colleagues analyzed data from the enteric disease cluster management database of the CDC Outbreak Response and Prevention Branch for all U.S. shigellosis clusters from 2011 to 2015 to investigate associations between transmission route and antimicrobial resistance.

Nineteen (39%) of the reported clusters were excluded in this analysis because of insufficient data on either antimicrobial resistance or both antimicrobial resistance and transmission. Of the 30 (61%) remaining clusters, two subclusters were further divided by transmission category, for a total of 32 clusters eligible for analysis. Clusters were linked to data from the National Antimicrobial Resistance Monitoring System for Enteric Bacteria, which tests sample Shigella isolates, to obtain information about the antimicrobial resistance phenotype associated with the cluster.

Robert D. Kirkcaldy, MD, MPH

Robert D. Kirkcaldy

Information about the sexual partners of patients with shigellosis is not routinely collected, the researchers wrote, but such information was sometimes available through interviews, medical records and sexual health databases. The researchers categorized a cluster's transmission as MSM-associated if any MSM-associated transmission was recorded for that cluster.

Of the 32 clusters, nine were caused by Shigella resistant to at least one of the following agents: ciprofloxacin (three clusters), ceftriaxone (two clusters) or azithromycin (seven clusters), and three of these clusters were resistant to more than one of these drugs.

Researchers observed resistance to at least one of these drugs in all seven MSM-associated clusters but in only two of the other 25 clusters (P < .001). None of the ten clusters with transmission associated with child care, camps or schools was caused by resistant strains. The prevalence of resistance between MSM-associated and other clusters significantly differed for ceftriaxone (29% vs. 0%), azithromycin (86% vs. 4%), azithromycin and either ciprofloxacin or ceftriaxone (43% vs. 0%), and any of these three drugs (100% vs. 8%).

Bowen and colleagues noted that the reasons for the association between drug-resistant shigellosis and MSM transmission are unknown and emphasized the need for further research to identify specific risk factors, understand clinical outcomes and develop effective interventions.

"Surveillance and interventions for shigellosis among MSM would be strengthened by more intensive collaboration between enteric disease and sexually transmitted disease programs within public health departments," they concluded. "Health messaging for MSM should include information about risk for and prevention of shigellosis and drug-resistant shigellosis." – by Sarah Kennedy

Disclosure: The researchers report no relevant financial disclosures.