Increasing resistance of Shigella to ciprofloxacin prompts new CDC guidance

With new strains of Shigella demonstrating reduced susceptibility to fluoroquinolones, the CDC recently recommended against routinely prescribing antibiotic therapy for infected patients.

Ciprofloxacin has been a key agent in managing Shigella infections, but recent data show that emerging strains are often resistant to the antibiotic, according to a Centers for Disease Control and Prevention (CDC) health advisory published on April 18.

The agency has found an increase in Shigella isolates in the U.S. with minimum inhibitory concentration (MIC) values between 0.12 and 1 µg/mL for ciprofloxacin. Preliminary data suggest that all isolates with MICs in this range have at least one quinolone resistance gene that is known to confer reduced susceptibility in enteric bacteria, according to the advisory.

Data from the National Antimicrobial Resistance Monitoring System suggest that many Shigella isolates with a quinolone resistance gene are also resistant to other commonly used antibiotics (e.g., azithromycin, trimethoprim-sulfamethoxazole, amoxicillin-clavulanic acid, and ampicillin), according to the advisory.

Generally, shigellosis is a self-limiting infection lasting five to seven days, but certain patients may need antimicrobial treatment, according to the CDC. The agency gave the following recommendations for diagnosis and management:

• If Shigella infection is suspected, order stool culture to obtain isolates for antimicrobial susceptibility testing (diagnostic testing without culture does not provide an isolate and cannot be used to assess susceptibility).
• When antimicrobial susceptibility testing is performed by broth microdilution, request ciprofloxacin testing that includes dilutions of 0.12 µg/mL and lower.
• Reserve antibiotic therapy for patients in whom it is clinically indicated or when public health officials advise treatment during an outbreak. Antibiotics are recommended for patients who are immunocompromised or who develop severe illness.
• When antibiotics are indicated, tailor antibiotic choice to antimicrobial susceptibility results as soon as possible while paying special attention to the MIC for fluoroquinolones. Avoid prescribing drugs in this class if the ciprofloxacin MIC is 0.12 µg/mL or higher (even if the lab report says the isolate is susceptible).
• If empiric treatment is indicated before susceptibility results are available, refer to recent hospital, clinical laboratory, or public health agency antibiograms.
• Order follow-up stool cultures in patients with shigellosis who have continued or worsening symptoms despite antibiotic therapy.
• Consult an infectious diseases subspecialist in cases where the isolate is resistant to multiple antibiotics and the appropriate treatment is unclear.
• All cases of shigellosis should be reported to local health departments.