International travel is a major risk factor for developing a range of infections, according to a study in a region of England.

Scientists found illness after travel abroad contributes substantially to the burden of infection in North East England. There has also been no reduction in the proportion of travel-associated infections in non-pandemic years since 2013. 

Laboratory reports of common notifiable enteric infections were linked to exposure data for cases reported between January 2013 and December 2022. Results were published in the journal Epidemiology and Infection.

Pathogens behind illness
In total, 9,358 lab-confirmed cases of gastrointestinal illness resulting from infection with Cryptosporidium, Giardia, hepatitis A, Salmonella, Shigella, Shiga toxin-producing E. coli (STEC), Vibrio, and Yersinia were reported in North East England residents. Routine exposure questionnaires were completed for 7,909 cases.

About 35 percent of cases reported international travel during their incubation period, although travel-associated cases were significantly reduced during the COVID-19 pandemic.

Between 2013 and 2019, half of Shigella and non-typhoidal Salmonella infections and a third of Giardia infections were reported following travel. The figure was under 30 percent for Cryptosporidium and above 20 percent for STEC infections.

In England, all lab-confirmed cases of notifiable enteric infections are reported to the UK Health Security Agency (UKHSA) from National Health Service (NHS) labs via the Second-Generation Surveillance System (SGSS). North East England has its own surveillance system, which links routinely collected SGSS data, lab typing data, and exposure data from standardized exposure questionnaires. 

Cases were defined as being associated with international travel if they had a completed exposure questionnaire and reported going outside the UK during a specified incubation period. The proportion of cases associated with international travel remained consistent between 2013 and 2019 with an average of 38 percent.

During England’s COVID-19 pandemic response in 2020 and 2021, infections were much lower than historic figures. In 2022, reports returned to pre-pandemic levels, mainly because of increases in travel-associated cases.

Risky destinations
The percentage of cases associated with travel remained consistent for most pathogens apart from Shigella, where a rise in UK-acquired cases has been observed since 2013, and STEC O157, where an increase in internationally acquired cases was reported in 2019.

Children aged under 9 and adults over 60 were significantly more likely to have acquired their infection in the UK.

Where such data was available, those of Asian ethnicity were more likely to have acquired their infection during international travel, with the rate of reported travel-associated infection in those of Asian ethnicity significantly higher than the rate for those of White ethnicity.

The most common destination reported by cases was Spain, followed by Turkey, India, and Egypt. Rates of illness were highest in people returning from Africa and Asia, with high rates also associated with all-inclusive tourist resorts like Turkey, Egypt, and the Dominican Republic.

Rates of hepatitis A and typhoidal Salmonella were highest in travelers to Asia, and rates of Vibrio were comparable for travelers to both Africa and Asia. Rates for all other pathogens were highest in people returning from Africa. The rate of acquiring non-typhoidal Salmonella was 527 times higher in travelers to Asia when compared to travelers to Europe.

More than 50 Salmonella and 41 Cryptosporidium clusters were identified. Salmonella outbreaks were mostly linked to travel to Turkey, Egypt, and Mexico. Cryptosporidium outbreaks were predominantly associated with Spain, Turkey, the Canary Islands, and Egypt.

“This work highlights the need to better understand risks while traveling to support the implementation of guidance and control measures to reduce the burden of illness in returning travelers,” said researchers.

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