A connection between extraintestinal infections and food is possible, but it is hard to prove a direct link, according to a Dutch agency.

Extraintestinal infections arise outside the intestines, especially in the urinary tract and bloodstream. An infection can occur because bacteria from feces have entered the urinary tract. There is increasing evidence that food can cause them.

The National Institute for Public Health and the Environment (RIVM) searched scientific literature to see whether there was a connection. The agency found indications, but no hard evidence, that food is a direct cause of these infections.

E. coli can cause both gastrointestinal and urinary tract infections. However, the E. coli strains associated with urinary tract infections differ from those behind gastrointestinal cases.

RIVM found extraintestinal pathogenic E. coli (ExPEC) appears to cause the most urinary tract and bloodstream infections in the Netherlands. So, scientists focused their search for a link between infections caused by ExPEC and food.

It is difficult to demonstrate whether bacteria that cause urinary tract infections come from food. To do this, it must be checked whether the bacterial strain in humans is the same as in food or animals. It then needs to be investigated whether people ate this food before developing an extra-intestinal infection. This kind of research takes a lot of time and money, said RIVM.

Looking at the evidence
Scientists first looked at which pathogens lead to urinary tract and bloodstream infections in the Netherlands using 2019 and 2022 data. E. coli was the top pathogen, while Klebsiella pneumoniae and Enterococcus faecalis were found less often.

The literature study analyzed articles on infections by ExPEC related to food, published from 2010 to February 2023. Poultry meat appeared to be the most significant potential source but this was based on indirect clues, said researchers. The role of eggs, raw milk, and fruit and vegetables is minimal, but there are only a limited number of studies.

The variable incubation period of extraintestinal pathogens, because they can live in the intestines without causing disease, makes it challenging to demonstrate a relationship with food.

Outbreaks of ExPEC have been described where there may have been a link to food but the source was not confirmed. Also, there was often incomplete data collection or reporting in these outbreak investigations.

Although similar strains appear to occur in animals and humans, there is no quantitative evidence of transmission of ExPEC through food and urinary tract infections with food as a direct source.

Ways to demonstrate the relationship between food and extraintestinal infections include detecting identical, or almost identical, strains in patients and food or animals and showing an epidemiological link between consumption of contaminated food products and extra-intestinal infections.

To gather more evidence, scientists said a database could be set up involving sequencing and analyzing ExPEC strains from clinical isolates, farm animals, and food. Based on this sequence data, any clusters can be monitored and investigated. Data could also be used for source attribution studies.

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