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Campylobacter (June 2026-)

Background 

  • Pathogen : Campylobacteriosis is a zoonotic disease caused by bacteria in the genus Campylobacter. Human gastrointestinal infections are mainly caused by Campylobacter jejuni and Campylobacter coli.

  • Transmission: Transmission occurs mainly through the faecal–oral route, most often through the consumption of contaminated food (especially poultry).Direct person-to-person transmission is uncommon, but can occur, usually between infected infants and those in contact with their diarrhoea. For more information, please see the dedicated page on the outbreak from the Swedish Health Agency (Folhälsomyndigheten) (available only in Swedish).

  • Sources and risk factors: The main recognised source is fresh poultry, particularly chicken, that has been insufficiently cooked or improperly handled. Cross-contamination of kitchen utensils, cutting boards, hands, and other foods during preparation can also lead to infection. Other identified sources include direct contact with animals, unpasteurised milk, and untreated water. Infections can result from only a small amount of bacteria, making food hygiene particularly important to prevent infection.

  • Seasonality: Campylobacter infection has a pronounced seasonal pattern in Sweden. Reported infections rise sharply during summer and early autumn, particularly from July to September. More than half of reported Swedish cases in recent years have been domestically acquired. The seasonal increase in human cases is associated with a corresponding increase in Campylobacter among chicken flocks. In 2026, surveillance data reported by the Swedish Veterinary Agency (available only in Swedish) showed increasing Campylobacter prevalence in poultry during July, coinciding with the rise in human cases.

Brief Summary of the Outbreak

The 2026 increase in Campylobacter infections in Sweden began around week 21 (late May). By week 23, 91 domestically acquired or unknown-country-of-infection cases had been reported across several regions. Folkhälsomyndigheten assessed the increase as expected and comparable with previous years, rather than identifying it as an unusual point-source outbreak.

Cases continued to increase through July. In week 28, more than 100 cases were reported, and by weeks 30–31 the number had reached the highest levels observed during the period. More than 150 cases were reported during week 31. The pattern corresponds closely to Sweden’s established summer Campylobacter season.

The increase also coincided with rising Campylobacter prevalence in Swedish chicken flocks during July. Folkhälsomyndigheten therefore continued to emphasise food-safety measures, particularly careful handling and thorough cooking of poultry, while noting that elevated case numbers could continue through August. Folkhälsomyndigheten has created a page on the outbreak.

Outbreak Timeline 

YEAR DATE OBSERVATION
2026 Late May An increase in Campylobacter cases became apparent. This marked the beginning of the seasonal rise in domestically acquired or unknown-country-of-infection cases.
2026 1-7 June 91 cases with Sweden as the reported country of infection, or with an unknown country of infection, were reported. Cases occurred across several Swedish regions
2026 17 June Folkhälsomyndigheten assessed the increase as expected and at levels similar to previous years. The agency highlighted the relationship between summer Campylobacter infections and increasing occurrence of the bacterium in chicken flocks.
2026 6-12 July Weekly cases increased to just over 100. July and August were identified as the period when domestically acquired Campylobacter cases are normally at their highest.
2026 13 July Folkhälsomyndigheten reported continued seasonal growth and expected the elevated number of cases to persist during the following weeks. Improperly handled or insufficiently cooked chicken remained an important known source.
2026 July Campylobacter prevalence in Swedish chicken flocks increased, according to surveillance reported by the Swedish Veterinary Agency. The rise coincided with increasing human infections.
2026 Early August The highest numbers of the period were recorded. During week 31 (27 July–2 August), more than 150 cases were reported.
2026 5 August Folkhälsomyndigheten confirmed that cases had continued increasing during July but that the pattern remained consistent with previous seasonal trends. Elevated reporting was expected to continue during August