A group of bacteria called Shigella is responsible for 500,000 cases of diarrhea in the US every year. Now a new report says a multi-drug resistant strain of the bug is entering the country in infected travelers and causing a series of outbreaks.

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The CDC recommend people wash their hands often with soap and water to prevent spread of the diarrhea illness shigellosis.

Shigella causes shigellosis - an intestinal illness that is accompanied by watery or bloody diarrhea, abdominal pain, fever and malaise.

The Centers for Disease Control and Prevention (CDC) say a strain of Shigella sonnei - the most common species of Shigella in the US - that is resistant to the antibiotic ciprofloxacin (Cipro) infected 243 people in 32 states and Puerto Rico between May 2014 and February 2015.

Shigella is one of the types of bacteria that cause intestinal illness in travelers going from developed countries to under-developed countries. This "traveler's diarrhea," is variously referred to as "Montezuma's revenge," or "Delhi belly," or the "Turkey trots."

The bacteria are found in water used for drinking, to wash food or to irrigate crops, that has been contaminated by human or animal stools.

Cipro is a first choice drug for treating shigellosis among adults in the US. Until recently, Cipro resistance was only found in around 2% of Shigella infections tested in the US.

In the new report - which describes investigations into recent clusters of Shigella infection in Massachusetts, California and Pennsylvania - the CDC say Cipro resistance was found in 90% of the samples tested.

Some people infected with Shigella only have mild symptoms, but this does not stop the bug from spreading. The report says that in these outbreaks, the bacteria spread easily in childcare facilities and among homeless people and gay and bisexual men.

Investigators found unique strain of Cipro-resistant Shigella

CDC Director Dr. Tom Frieden says the outbreaks they investigated are a troubling trend:

"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."

Dr. Frieden states the US is moving quickly to put in place a national plan to curb antibiotic resistance, because "we can't take for granted that we'll always have the drugs we need to fight common infections."

In the US, most strains of Shigella are already resistant to the antibiotics ampicillin and trimethoprim/sulfamethoxazole. Around the world, Shigella is becoming more resistant to Cipro, which is often prescribed to people traveling out of the US in case they develop diarrhea while abroad.

The report describes how through the CDC's PulseNet lab network, it was possible to identify an increase in shigellosis cases caused by a unique strain of Cipro-resistant Shigella. About half of the cases were people known to have returned from the Dominican Republic, India and other places outside the US.

The CDC recommend good hygiene habits to prevent the spread of Shigella, including:

  • Wash hands frequently with soap and water
  • Always wash hands with soap and water after using the toilet, and before preparing food and eating
  • If your child is sick with diarrhea, keep them home and away from childcare and group activities
  • Don't prepare food for others if you have diarrhea
  • Avoid swimming pools and other public water places for a few weeks as you recover from a diarrhea illness.

Dr. Anna Bowen, a medical officer in CDC's Waterborne Diseases Prevention Branch, and lead author of the report, says:

"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."

Scientists are starting to discover that antibiotic use - and overuse especially - is linked to a range of problems that affect, among other things, the immune system, glucose metabolism, food digestion, gut health and behavior.

For instance, in February 2015, Medical News Today reported another study that showed antibiotic use has more more unwanted side effects on the gut than previously thought. In that study, led by the College of Pharmacy at Oregon State University, Corville, researchers tested the effect of four antibiotics commonly given to lab animals.

Previously, it was thought the drugs only killed bacteria and blocked some immune functions in the gut. However, the study found they also destroy cells in the lining of the gut.