The United States is currently experiencing an outbreak of shigellosis caused by a strain of the Shigella sonnei bacteria that is resistant to ciprofloxacin, the most commonly prescribed antimicrobial treatment for shigellosis.

In its Morbidity and Mortality Weekly Report , the CDC revealed that 243 individuals in 32 states and the territory of Puerto Rico have come down with shigellosis between May 2014 and February 2015. Of those 243 cases, 126 isolates were tested and 109 (87%) of those were found to be nonsusceptible to ciprofloxacin. The largest clusters of the disease were found in Massachusetts (45 cases), California (25 cases), and Pennsylvania (18 cases).

Ninety-five of the cases associated with the current outbreak were traced back to the homeless population of San Francisco; about half of the remaining cases were attributed to international travelers – specifically, those visiting the Dominican Republic and India – who contracted the bacteria while abroad and unknowingly brought it to the United States. The disease is known to spread quickly in populations of children who attend child care facilities, homeless individuals, and men who have sex with men.

“These outbreaks show a troubling trend in Shigella infections in the United States,” Dr. Thomas Frieden, CDC director, said in a statement. “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. We’re moving quickly to implement a national strategy to curb antibiotic resistance because we can’t take for granted that we’ll always have the drugs we need to fight common infections.”

Shigellosis causes an estimated 500,000 cases of diarrhea in the United States each year. To help curb the growing number of shigellosis cases, the CDC recommends that international travelers wash their hands meticulously while abroad, and follow strict dietary precautions, such as eating hot foods and drinking beverages only from sealed containers, especially when consuming water.