Photographer: Scimat/Science Source

America's Got a New Superbug to Fight

Wash your hands

Meet America’s latest superbug: Shigella sonnei. It’s a strain of bacteria that causes severe diarrhea in about half a million people in the U.S. each year. Most of the time, it's treated effectively with an antibiotic called Cipro. But that’s changing, and it’s bad news.

Since last May, health authorities have discovered 243 cases of a strain that resists treatment with Cipro. That includes big clusters in Massachusetts, Pennsylvania, and San Francisco, where an outbreak linked to the homeless population sickened 95 people between November and January. This strain is usually introduced by international travelers, but the Centers for Disease Control reports today that "it is now circulating domestically.”

Source: CDC

Shigella isn't as scary as some of the other drug-resistant germs now endemic to the U.S., such as CRE (Carbapenem-resistant enterobacteriaceae), which is frequently spread in health-care settings and often deadly. But any new infections that defy our antibiotic arsenal are troubling. The germ is carried by stool and can spread easily through contaminated food and water or inadequate sanitation. "Getting just a little bit of the Shigella bacteria into your mouth is enough to cause infection," according to the National Library of Medicine. A gulp of water in a dirty swimming pool could be enough. Child-care facilities, homeless communities, and men who have sex with men are particularly at risk, according to the CDC.

While it's not deadly and the infection usually clears up on its own, Shigella isn't pretty. Symptoms begin soon after infection and include abdominal pain, diarrhea that's often bloody, cramps, and other unpleasantness. Severe cases are treated with antibiotics, and Americans going abroad are often given Cipro to take in case they get diarrhea. The CDC says more research is needed to determine whether that practice is contributing to resistance.

Shigella sonnei is related to another group of Shigella bacteria that can cause dysentery. The bug takes its name from the Japanese scientist who identified it in 1897, Kyoshi Shiga. Shigella is already resistant to some common antibiotics, but Cipro has been generally effective in the U.S.

The report on Shigella comes a week after the White House published a national strategy to combat antibiotic resistance. Drug-resistant bacteria are responsible for an estimated 23,000 deaths and 2 million illnesses each year. The Obama administration's plan calls for more prudent use of antibiotics, better surveillance to track pathogens, and increased research for new antibiotics. Critics who include New York Congresswoman Louise Slaughter, a Democrat and microbiologist, said the plan falls short in curbing the use of antibiotics to promote growth in farm animals. About 80 percent of the antibiotics used in the U.S. are for agriculture, generally not to treat sick animals but to prevent infection and make them grow faster.

The World Health Organization called antibiotic resistance "an increasingly serious threat to global public health." Fighting it requires collective action to reduce improper use of antibiotics and control the spread of infections. It's likely that Shigella won't be the last germ that increasingly withstands our arsenal of treatments. Wash your hands, and be careful in the pool.

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