Travelers Bringing Drug-Resistant Shigella Back Into the US

Pam Harrison

April 03, 2015

Recent clusters of ciprofloxacin-resistant Shigella sonnei have been identified in the United States by the Centers for Disease Control and Prevention (CDC) that are largely the result of international travelers bringing resistant bacteria back into the country and infecting others, according to an article published in the April 3 issue of the Morbidity and Mortality Weekly Report.

From May 2014 to February 2015, PulseNet, the national molecular subtyping network for foodborne disease, identified 157 cases of ciprofloxacin-resistant S sonnei in 32 states and Puerto Rico, approximately half of which were associated with international travel.

"Most cases were reported in Massachusetts (45 cases), California (25) and Pennsylvania (18)," Anna Bowen, MD, MPH, from the National Center for Emerging, Zoonotic and Infectious Disease, CDC, Atlanta, Georgia, and colleagues write.

At the same time, public health officials in San Francisco, California, identified an outbreak of 95 cases of ciprofloxacin-resistant shigellosis, nine of which were also identified by PulseNet, bringing the total number of S sonnei cases in the United States to 243.

The 95 cases detected in San Francisco were part of an outbreak of ciprofloxacin-resistant shigellosis associated with the homeless population in the city.

Eighty-seven percent of 126 isolates tested were not susceptible to ciprofloxacin, investigators add. Ciprofloxacin is the drug of choice to treat shigellosis in adult patients in the United States.

"Drug-resistant infections are harder to treat and because Shigella spreads so easily between people, the potential for more — and larger — outbreaks is a real concern," Tom Frieden, MD, MPH, director of the CDC, said in a CDC news release.

Among the 41 patients for whom such information was available, the median duration of illness was 7 days.

Nineteen of 88 patients for whom such information was available were hospitalized for their illness.

Information was available on 75 patients who had traveled during the study interval; destinations included the Dominican Republic, Haiti, India, and Morocco.

Most travelers to the Dominican Republic stayed at resorts in the Punta Cana, the investigators observe.

"The increase in drug-resistant Shigella makes it even more critical to prevent shigellosis from spreading," Dr Bowen said in the news release.

"Washing your hands with soap and water is important for everyone. Also, international travelers can protect themselves by choosing hot foods and drinking only from sealed containers."

The CDC authors also recommend that healthcare providers culture stool specimens of patients with symptoms consistent with shigellosis and reculture the stool of those who fail to improve after antimicrobial therapy.

They also suggest that physicians reserve antimicrobial treatment only for patients who are immunocompromised or for those with severe shigellosis and use antimicrobial susceptibility data strategically to guide therapy to help preserve the utility of antibiotics.

Diarrhea caused by S sonnei typically resolves without treatment, but patients with mild illness are often treated with antimicrobials because treatment can reduce the duration of the illness, as well as the shedding of S sonnei in feces.

Resistance to other antimicrobials including ampicillin and trimethoprim/sulfamethoxazole is already common among S sonnei bacteria in the United States.

Shigella causes an estimated 500,000 cases of diarrhea in the United States every year.

The authors have disclosed no relevant financial relationships.

Morb Mortal Wkly Rep. 2015;64:318-320. Full text

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