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US health officials are warning of a rise in a strain of a drug-resistant stomach bug that infects thousands of Americans each year.

Shigella bacteria causes fever, diarrhoea and stomach pain. Since 2015, officials have noted a rise in cases linked to the drug-resistant strain.

The inability to treat infections with medication led health officials to call it a "serious public health threat".

Without effective treatment, it could cause severe illness or even death.

In a statement on Friday, the US Centers for Disease Control and Prevention (CDC) said that while none of the infections recorded in 2015 were tied to the Shigella XDR strain, 5% of cases were linked to it in 2022.

In 2019, 1% of all US cases were linked to the strain, which is resistant to the five antibiotics that are most commonly used to treat it.

Shigella spreads "easily" through direct and surface contact with an infected person's faeces, the CDC says. It can lead to a form of dysentery named shigellosis, which is considered one of the leading causes of death linked to diarrhoea around the world.

Many cases can be managed through proper hydration and rest. Officials say it can be prevented by frequent hand washing. Currently, it causes less than five deaths in the US per year.

The increase in the XDR strain has most commonly been seen in homeless people, international travellers, men who have sex with men, and immunocompromised people, the CDC said.

"Given these potentially serious public health concerns, CDC asks healthcare professionals to be vigilant about suspecting and reporting cases of XDR Shigella infection to their local or state health department and educating patients and communities at increased risk about prevention and transmission," the agency said.

Officials in the UK also warned last year of a "unusually high number of cases" linked to the XDR strain.