BACKGROUND: Shigella is a leading cause of enteric infections in the United States. The annual incidence of shigellosis is approximately 4.82 cases per 100,000 individuals. Recently, Shigella species resistant to broad-spectrum antibiotics have been associated with outbreaks in several jurisdictions including a cluster of ciprofloxacin-resistant Shigella sonneiin Pennsylvania. However, statewide surveillance for antimicrobial-resistant Shigella infections is limited.
METHODS: From a collection of Shigella isolates received during 2006-2014, we tested 204 samples equally categorized into overseas travel-associated and domestically acquired infections (n=102 for each category). We analyzed isolates for antimicrobial resistance profiles, geographic distributions, and pulsed-field gel electrophoresis (PFGE) patterns.
RESULTS: Eighty-one (79.4%) of the Shigella isolates associated with international travel were resistant to multiple antibiotics, compared to 53 (52.1%) of the infections transmitted in domestic settings. Eighty (78.4%) of isolates associated with international travel demonstrated resistance to aminoglycosides and tetracyclines, and 20 (19.6%) isolates were resistant to quinolones. Among 95 isolates from overseas-acquired infections that were caused by S. flexneri and S. sonnei, 27.3% had 6 PFGE patterns that were observed ≥3 times. Among isolates associated with domestic settings, 94 (92.2%) were resistant to aminoglycosides, and five isolates from adult male patients were resistant to azithromycin. Among 98 domestically acquired S. flexneri and S. sonnei infections, 39 (39.8%) were caused by 6 distinct PFGE patterns. Among 95 infections acquired during overseas travel, 22 (23.2%) were caused by S. sonnei isolates. Shigella isolates with shared PFGE patterns had different antimicrobial resistant profiles.
CONCLUSIONS: Widespread antimicrobial resistance to clinically important drugs was demonstrated among Shigella isolates associated with both travel and domestic settings. The variations in antimicrobial resistance profiles suggest limitations of PFGE in revealing underlying genetic differences among Shigella isolates. There is need for continued surveillance with precise genome sequence analysis to elucidate the spread of multi-drug resistant shigellosis.