The Centers for Disease Control and Prevention has identified an increase in Shigella isolates with reduced susceptibility to ciprofloxacin, and has released an official health advisory outlining new recommendations for clinical diagnosis, management, and reporting, as well as for laboratories and public health officials.
The Shigella isolates of concern in the United States have minimum inhibitory concentration (MIC) values of 0.12-1 mcg/mL for ciprofloxacin, which is within the range considered susceptible. These strains, however, “often have a quinolone resistance gene that may lead to clinically significant reduced susceptibility to fluoroquinolone antibiotics,” such as ciprofloxacin, according to the CDC advisory.
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It is possible that strains with MIC in the 0.12-1 mcg/mL range may have worse clinical outcome or increased risk of transmission, so the CDC made the following recommendations to clinicians:
• Order a stool culture to obtain isolates for antimicrobial susceptibility testing in suspected cases.
• Order antimicrobial susceptibility testing when ordering a stool culture for Shigella.
• Avoid routine prescribing of antibiotic therapy for Shigella infection, instead reserving antibiotics for patients with a clinical indication or when advised by public health officials in an outbreak setting.
• Tailor antibiotic choice (when antibiotics are indicated) to susceptibility results as soon as possible – with special attention given to the MIC for fluoroquinolone antibiotics.
• Obtain follow-up stool cultures in shigellosis patients who have continued or worsening symptoms despite antibiotic therapy.
• Consult local or state health departments for guidance regarding when patients may return to child care, school, or work.
• Counsel patients with active diarrhea on how they can prevent spreading the infection to others, regardless of whether antibiotic treatment is prescribed.
Additionally, the CDC noted that shigellosis is a nationally notifiable condition; all cases should be reported to the local health department. If a patient with shigellosis and a ciprofloxacin MIC of 0.12-1 mcg/mL is identified, this information should be included in the report to facilitate further testing of the isolate.
The CDC reported that it is working with state and local public health departments and clinical partners to determine if outcomes are indeed worse for patients treated with ciprofloxacin for Shigella strains harboring a quinolone resistance gene, and it will continue to monitor trends in susceptibility of Shigella isolates and to perform genetic testing on select strains to confirm the presence and type of resistance genes.
