International travel leads to outbreak of resistant shigellosis

SAN DIEGO — An outbreak of Shigella sonnei affecting more than 300 people appears to have been repeatedly imported by international travels and clustered within multiple communities of men who have sex with men, according to data presented at IDWeek 2015.

In addition, testing of the strain revealed frequent resistance to ciprofloxacin and sub-clusters of isolates resistant to a number of other antimicrobial agents, according to Anna Bowen, MD, MPH, of the CDC.

“Currently, there are high rates of resistance to ampicillin and trimethoprim/sulfamethoxazole [TMP/SMX] in the U.S., ranging from about 40% to 80%,” Bowen said during a presentation. “Less commonly, there is resistance to azithromycin (3.8%), ciprofloxacin (3.5%) and ceftriaxone (1.2%). These modest rates of resistance, however, translate into large numbers of cases, with approximately 27,000 per year in this country, and there are hints that these numbers are increasing.”

Bowen and colleagues examined cases of S. sonnei infection matching one of five pulsed-field gel electrophoresis (PFGE) patterns detected from May 1, 2014 to May 31, 2015, as well as those identified during a San Francisco outbreak within homeless populations between Nov. 1, 2014 and April 15, 2015. Data on these cases were collected from the CDC’s PulseNet PFGE surveillance system and the San Francisco Department of Public Health, with antimicrobial susceptibility testing data examined if available.

There were 307 identified cases spread across 34 states and Puerto Rico, according to Bowen. Median duration of illness was 7 days, 97% of isolates were obtained from stool, and hospitalization occurred among 25% of patients for whom clinical information was available. International travel was common among cases, Bowen said, with various destinations such as Hispaniola and India suggesting no common source of illness.

More than two-thirds of men whose sexual practice data was available self-identified as MSM, with many reporting high-risk behavior with persons not identified in the outbreak case count. These MSM represented several clustered, domestically acquired cases within six states spread throughout the country.

Antimicrobial resistance testing revealed 86% of isolates to be resistant to ciprofloxacin. Among these a sub-cluster of five cases resistant to ciprofloxacin, ampicillin, TMP/SMX with decreased susceptibility to azithromycin also was identified, which Bowen said is especially worrisome.

“This outbreak reminds us again of the importance of international travel in the spread of drug-resistant pathogens,” Bowen said. “Actions we must take include educating travelers about food, water and hand hygiene precautions, and warning them that they’re at risk for more than just a little travelers’ diarrhea, but rather multidrug-resistant infections that can be difficult to treat and easy to spread to their families or communities.” – by Dave Muoio

Reference:

Bowen A, et al. Abstract 1967. Presented at: IDWeek; Oct. 7-11, 2015; San Diego.

Disclosure: Bowen reports collaboration and research support from Procter & Gamble. All other researchers report no relevant financial disclosures.