Last year, Colorado recorded an unusually high number of infections with a bacteria that causes bloody diarrhea, including at least one cluster from a strain that’s resistant to most antibiotics.
In a typical year, about 250 people in Colorado are diagnosed with shigellosis, an intestinal illness caused by a few species of shigella bacteria. In 2022, 373 people were, including 32 infected with bacteria that were resistant to the five antibiotics commonly used against shigella, said Rachel Jervis, manager of the foodborne, enteric and waterborne diseases program at the Colorado Department of Public Health and Environment.
There’s likely some underreporting, though people are more likely to seek care for shigellosis than for other infections, given its relatively long course and that it’s not uncommon to see bleeding, she said.
Shigellosis causes prolonged diarrhea, abdominal cramping and fever. Most people recover without any specific treatment, or with intravenous fluids to prevent dehydration. People who have compromised immune systems or who are older have a higher risk of severe illness, though, and antibiotics may be necessary for them, Jervis said.
“Having drug-resistant shigella means doctors have fewer tools in their toolbox,” she said.
Nationwide, the Centers for Disease Control and Prevention reported 239 people have been infected with extensively drug-resistant, or XDR, shigella strains since 2015, with 90% of those cases reported between 2020 and 2022. Data from the current year isn’t available yet.
Colorado had the second-highest total, behind California, with the 32 recorded in 2022 and four in previous years. The state’s public health lab sequences every shigella case for antibiotic resistance, while some states only test a portion of the samples they receive, Jervis said.
“What we have is real and it’s happening, but it’s difficult to compare to what’s happening in other states,” she said.
Right now, there’s no protocol for treating people who become severely ill with the most drug-resistant strain, according to the CDC. Two types of antibiotics are available in the United States and might work, but haven’t been extensively studied against XDR shigella.
The CDC also raised concerns that the drug-resistant shigella could swap genes with bacteria that have a higher fatality rate, so that antibiotics no longer work against the illnesses they cause.
The United States sees about 450,000 shigella infections and 5,400 hospitalizations in a typical year, according to CDC estimates. Shigellosis is most common in children under 5, but kids accounted for only about 5% of XDR infections. Most of the resistant infections were in adult men who have sex with men, people with HIV, those who recently traveled overseas and people who are homeless.
The bacteria is spread when trace amounts of feces get into the mouth, Jervis said. That can happen when people touch an infected person’s hands, if not thoroughly washed, and then eat or touch their mouths; by touching objects an infected person touched; by changing diapers or providing toileting assistance to an infected person; by eating food prepared by someone who was sick; by swimming in water after an infected person did; and by sexual contact.
In some cases, the state was able to find a specific mode of transmission, including sex, but in others, there were too many possibilities, she said.
“When people are sexual partners, they’re sharing a lot of other contact,” she said.
The CDC recommends that people who had any strain of shigella abstain from sex, not prepare food for others and avoid water recreation for two weeks after their diarrhea stops. It also advises them to use condoms or another barrier method and to carefully wash body parts and intimate toys after resuming sex.
In August, the state’s public health lab found four shigella cases that were nearly identical genetically, all in men in the Denver area, Jervis said on a CDC-hosted call to educate health care providers in February. Bacteria pick up mutations over time, so when their genetic material is highly similar, that suggests people were infected in the same event, or that one of the people infected the others.
The CDC reported the Colorado cases were part of a multi-state outbreak in early September. Altogether, the state found 17 cases linked to the cluster in people who were infected between July and December, Jervis said. Eight people were hospitalized, but no one died.
Of those 17 people, 11 lived in Denver, with the others spread along the Front Range. Fourteen were men, and 10 reported they had male sexual partners. They also were more likely to report being homeless, using multiple substances and having compromised immune systems than the general population.
In October, the state health department sent a notice to providers advising them to request testing to find out if their patients’ shigella infection is still susceptible to antibiotics. It also reminded them that they’re required to report shigella cases and that juvenile patients shouldn’t return to school or child care until cleared by public health officials. Whether adults can return to work depends on their job, with people working in food service or health care needing to stay home longer.
So far this year, there are fewer shigellosis cases, but it’s not clear how much of that is due to the disease’s tendency to peak in the summer, Jervis said. People who have persistent diarrhea should get tested, so they know if they need to take additional precautions to avoid infecting others, she said.
“It’s really important to seek medical care if your symptoms aren’t resolving,” she said.
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