More Campylobacter outbreaks than expected – and more people fall ill when it rains

Campylobacter remains the bacterium that most frequently causes gastrointestinal infection in the Danish population as well as in the rest of the Western world. A new report from Statens Serum Institut (SSI) shows that the number of patients follows an increasing trend. In 2019, more than 5,300 patients were diagnosed in Denmark. That is more than have ever been recorded previously. Therefore, several studies have been undertaken to enhance our understanding of how Campylobacter is transmitted.

Many outbreaks

In 2019, for the first time Campylobacter isolates were collected from a sample of Danish patients and routinely analysed by whole-genome sequencing. This revealed that various small and one unusually large outbreak occurred - a fact which would otherwise have remained unknown. These outbreaks were mainly due to chicken meat produced in Denmark.

“Previously, it was assumed that Campylobacter only very rarely causes disease outbreaks. But our results demonstrate that many Campylobacter outbreaks occur in the Danish population – and that these outbreaks are predominantly caused by foods”, notes Section Head Eva Møller Nielsen, who spearheads the SSI’s activities to perform genome sequencing of Campylobacter.

More fall ill when it has been raining

Even so, Campylobacter is not exclusively transmitted through food. The bacterium is also transmitted from the exterior environment through contact to dirt, water, sand and animals. This was, among others, evident from another study in which information about where and when patients had fallen ill was compared with weather data. This was done for a number of years for Denmark and the other Scandinavian countries. Among others, the results demonstrated that more people fell ill in the wake of periods with heavy rain. This means that more patients may be expected in years to come if climate changes, as has been forecast, will bring more rain and more periods with heavy rain.

“It seems that climate changes will mean that the high season for infection with Campylobacter may extend beyond the summer months, and in general that more people will be affected by the infections in years to come than is currently the case. Analyses like these may prepare us for the consequences of climate changes in terms of the future number of gastrointestinal infections,” notes Senior Researcher Katrin Kuhn from the SSI, who has analysed Nordic climate data and infection data.

Read more

Read more about the two studies and the number of Campylobacter cases in 2018 and 2019 in EPI-NEWS 6/2020.