Drug-resistant Shigella Infection Risk Among Men Who have Sex with Men

In the United States, Shigellosis causes approximately 500,000 illnesses annually and resistance to drugs to treat the infection, such as ciprofloxacin, ceftriaxone, and azithromycin, is emerging. Recently, researchers from the Centers for Disease Control and Prevention (CDC) investigated associations between transmission route and antimicrobial resistance among 32 clusters reported between 2011—2015.

According to the investigation, “Of 32 clusters, 9 were caused by shigellae resistant to ciprofloxacin (3 clusters), ceftriaxone (2 clusters), or azithromycin (7 clusters); 3 clusters were resistant to >1 of these drugs. We observed resistance to any of these drugs in all 7 clusters among men who have sex with men (MSM) but in only 2 of the other 25 clusters (p<0.001).” Azithromycin resistance was more common among the MSM-associated clusters.

As few as 10 bacteria can cause infection making shigellosis outbreaks typically large and difficult to control unless interventions are implemented early. Bloodstream infection is not common among those individuals with normal immune systems; however, patients are usually still treated with antimicrobial medications to reduce the duration of the illness duration and possible transmission to others.

The researchers noted that although the results of the study suggest that shigellae with antimicrobial drug resistance circulated predominantly among MSM, these strains are likely to emerge in other populations as well. In addition, the researchers advised that, “Efforts to facilitate improved hygiene practices among persons at high risk for shigellosis or at high risk for transmitting shigellosis to others (eg, child care attendees, staff, and parents; marginally housed persons; international travelers; and food handlers) are needed now to limit transmission when multidrug-resistant Shigella strains inevitably begin circulating among these populations.”

The information used in the study was limited because the CDC Outbreak Response and Prevention Branch (ORPB) cluster management database, which serves as a means to guide response, likely only contained a fraction of the shigellosis clusters. Likewise, because most public health jurisdictions do not perform pulsed-field gel electrophoresis (PFGE) on shigellae, the number of clusters and complete detail on each cluster was likely not complete.

The researchers suggest further characterizing isolates by PFGE or whole-genome sequencing will assist health departments with cluster detection and control.

Prevention of shigellosis is critical because “alternative treatment options are limited for persons infected with ciprofloxacin-, ceftriaxone-, or azithromycin-resistant shigellae.” Clinicians should culture feces and obtain sex histories in adults with suspected infection. In addition, they should discuss shigellosis prevention and choose treatments according to antimicrobial drug susceptibility. Clinicians should also counsel all patients suspected of shigellosis about meticulous handwashing and hygiene.

Treatment, if necessary, should be based on the results of antimicrobial susceptibility testing.