Shigella species epidemiology and antimicrobial susceptibility: the implications of emerging azithromycin resistance for guiding treatment, guidelines and breakpoints

Objectives: To examine antimicrobial susceptibility patterns and predictors of resistance among Shigella isolates in New South Wales (NSW), Australia during 2013-14 with emphasis on azithromycin. Methods: Cross-sectional analysis of all shigellosis cases (160) notified to public health authorities in NSW, Australia was performed. Results: Among 160 Shigella isolates tested, 139 (86.9%) were susceptible to azithromycin, 104 (65.0%) to ciprofloxacin and 38 (23.7%) to co-trimoxazole. Ciprofloxacin resistance was 1.9 times more common in infections acquired in Australia compared with those acquired overseas, while azithromycin resistance was 8.5 times more common in males. Conclusions: We recommend ongoing reconsideration of guidelines for the treatment of shigellosis based on emerging resistance patterns. First-line therapy may need to be reconsidered based on local resistance rates due to common resistance to co-trimoxazole and ciprofloxacin. We recommend culture and susceptibility testing for suspected and proven shigellosis. Azithromycin susceptibility breakpoints for Shigella species may need to be species specific.