Travellers may be causing a rise in the spread of antibiotic resistant bacteria.

The use of antibiotics for diarrhoea placed visitors to developing parts of the world at a greater risk of contracting “superbugs” and spreading when they return back home.

Researchers are calling for greater caution in the use of antibiotics for traveller’s diarrhoea, unless severely needed, to stop the spread of antibiotic resistant bacteria worldwide.

Finnish researchers collected stool samples from more than 400 people before and after they travelled out of Scandinavia to investigate if their gut had become colonised by a resistant bacteria from the Enterobacteriaceae family, which produces an enzyme, extended-spectrum beta-lactamase (ESBL), allowing microorganisms to have antibiotic resistance.

ESBL producing bacteria has been rated a “serious concern and significant threat” to public health by the American centres for disease control and prevention.

It was found 21% of those who had travelled to tropical and subtropical areas had contracted ESBL-producing bacteria. Of those who had taken antibiotics for diarrhoea, almost 40% of them had been colonised by such bacteria.

This was particularly high in South Asia with 80% of travellers who had taken antibiotics for traveller’s diarrhoea found to have ESBL-producing bacteria in their gut.

Associate professor in infectious diseases and Helsinki University hospital, Dr Anu Kantele, said if the number of travellers been higher, some would have developed infections.

“More than 300m people visit these high risk regions every year. If approximately 20% of them are colonised with the bugs, these are huge numbers,” he said.