Increase in Shigellosis with Decreased Susceptibility to Azithromycin Among Men Who Have Sex with Men in Chicago

BACKGROUND: During summer 2014, the Chicago Department of Public Health (CDPH) began seeing an increase in Shigella sonnei cases. From July 31–October 31, 2014, 57 Shigella sonneicases were reported in Chicago as compared to an average of 30 cases during the same period in 2010–2013; adult males were disproportionately affected. CDPH investigated these cases to assess epidemiological links. 

METHODS: CDPH selected all Shigella sonneicases among adult males reported to CDPH from July 31–October 27, 2014 (n=23) and monitored demographic trends in shigellosis surveillance data. We developed a questionnaire to assess common exposures. The Illinois Department of Public of Health laboratory performed pulsed-field gel electrophoresis (PFGE) analysis on available isolates (n=17). Ten isolates were selected for antimicrobial susceptibility testing (AST) by CDC’s National Antimicrobial Resistance Monitoring System (NARMS).

RESULTS: In all 23 cases, clinical illness was limited to gastroenteritis with 5 (26%) of 19 cases reporting bloody diarrhea. Nine (39%) patients were hospitalized. Median patient age was 35 years (range 23–73 years) and 70% were non-Hispanic white. Ten (43%) cases were HIV+.  Eleven (85%) of 13 case-patients who provided information on sexual practices engaged in a same-sex sexual encounter the week before onset. Case-patients reported visiting bars/clubs or living in two communities known to be frequented by men who have sex with men (MSM). Most sexual partners were anonymous; two case-patients utilized mobile dating applications for finding partners. Of 17 isolates with PFGE data, 10 fell into a predominant PFGE cluster. Eight of the 10 isolates submitted to NARMS were in the main PFGE cluster and had decreased susceptibility to azithromycin (DSA); one was resistant to ciprofloxacin. Of eight patients with DSA shigellosis, five were MSM and one was heterosexual; five were HIV+. As of March 1, 2015, CDPH continued to see an elevated number of men with Shigella sonneiinfection.

CONCLUSIONS: An outbreak of DSA shigellosis is ongoing among the MSM population in Chicago. Half the patients with DSA shigellosis are HIV+ and report recent anonymous sexual partners.  CDPH alerted healthcare providers to these findings and recommended stool cultures with AST to guide treatment, particularly among those with treatment failure or prolonged illness. Additionally, CDPH is working with CDC to determine the outbreak’s extent and to implement public health messaging on mobile dating applications. More information about clinical outcomes of patients with DSA shigellosis is needed to establish azithromycin clinical breakpoints for Shigella AST.