Campylobacter types found in fresh chicken often matched those from ill people showing poultry is still a common source of infection in Sweden.

Researchers studied the genetic similarity between Campylobacter from retail chicken meat and in infected people. It is the third year the Public Health Agency (Folkhälsomyndigheten) and Swedish Food Agency (Livsmedelsverket) have done such a survey and results are largely in line with 2017 and 2018.

The study showed the same varieties of Campylobacter in fresh chicken meat at the end of summer 2019 were also found in many of those who became ill with Campylobacter at the same time. Although one-third of cases could be linked to chicken, no ongoing outbreak was detected.

Product testing
A total of 100 chicken meat samples were analyzed from 40 different stores in the Stockholm and Uppsala region and Campylobacter was detected in 51 of them. Two isolates from foreign chicken could not be typed but of the remaining 49, all were Campylobacter jejuni except one Campylobacter coli isolate.

A majority of cases related to chicken were associated with Swedish conventionally bred chicken (88 percent) and especially to products from Sweden’s largest slaughterhouse. The organic chicken was linked to a few cases, while imported poultry was not associated with any infection. This finding is probably due to the fact Swedish products dominate the market.

A total of 8,132 cases of campylobacteriosis were reported in 2018 compared to 10,608 in 2017. Most cases are considered sporadic but in the past few years, several large outbreaks linked to domestically produced chicken have occurred.

Prevalence in chicken flocks has decreased in recent years, which also reduces the risk of people becoming infected, according to the Swedish Food Agency.

The human factor
Infection is most common during August, which coincides with an increase in Campylobacter positive chicken flocks. Typing with whole-genome sequencing showed that 20 percent of the human isolates clustered with one or more other isolates during low season in March.

In the low season, Campylobacter isolates were obtained from 14 of Sweden’s 21 regions. A total of 25 isolates were typed from cases infected in Sweden. All of them were Campylobacter jejuni.

From the collection for week 34, Campylobacter isolates came from 18 of 21 regions. A total of 112 isolates were typed for cases infected in Sweden. One isolate was Campylobacter coli while all the others were Campylobacter jejuni.

In 2019, all human clusters included isolates from different regions, which indicates a common source of infection with a wide geographical distribution.

Researchers said the comparison of human and retail chicken isolates indicates that if a reduction of Campylobacter in chicken production is achieved this will have a direct impact on the number of people who become infected.

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