Listeria rise continues but other pathogens decline in Sweden

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The number of people infected with E. coli, Salmonella, and Campylobacter decreased but there was an increase for Listeria in Sweden in 2019.

The report, published by the National Veterinary Institute (SVA), also noted record highs for Yersinia and cryptosporidium.

Domestic incidence of campylobacteriosis was lower in 2019 compared with the 8,132 cases in 2018 and in recent years when several large outbreaks were related to domestically produced chicken. A total of 6,693 cases were reported in 2019, of which, 2,865 were domestic. For these, the median age was 47 with a range from 0 to 97 years old. Like previous years, the domestic incidence was higher among adults than children, and more men (56 percent) than women were reported.

In August 2019, a survey by the Swedish Food Agency (Livsmedelsverket) saw 100 samples of fresh chicken meat collected at retail and analyzed. Campylobacter was detected in 51 percent of them and levels exceeded 10 CFU/g in 13 percent of samples. Food businesses at five slaughterhouses collected 419 pooled neck skin samples. Test results were satisfactory and only seven exceeded the limit of 1,000 CFU/g.

Increasing Listeria trend
During 2019 listeriosis rose slightly compared to 2018 and there is an increasing trend in Sweden and other EU countries. In total, 113 cases were reported compared to 89 in 2018. Twenty people died within one month of diagnosis. The median age was 75 and as in previous years, most were people over 80 years old. Sixty-four cases were females and 49 were males.

One Swedish case was connected to a Norwegian outbreak from rakfisk, a fermented fish product. The fish to be fermented in Norway was produced in Sweden and the outbreak strain was found at the Swedish establishment. Sweden had four historical cases from 2015 to 2016 in an outbreak linked to cold-smoked or gravad fish from a production plant in Estonia. A rare strain of Listeria monocytogenes in Sweden (ST 91) caused one case of listeriosis. A sample of unpasteurized French cheese, Brie de Meaux, from the freezer of the patient was positive for the outbreak strain.

“In 2019 as in previous years, typing using WGS indicated that many of the linked cases were geographically dispersed and that the sources of infection had persisted for many years,” according to the report.

Shiga toxin-producing E. coli (STEC)
In 2019, 756 STEC cases were reported of which 415 were domestic, compared to 892 cases of which 627 were domestic in 2018. The long-term trend for STEC infection in Sweden is rising. As in previous years, the incidence was highest in children. In total 80 different serotypes were identified. The most common were O157: H7, O26: H11, and O103: H2.

STEC-associated hemolytic uremic syndrome (HUS) was reported in 22 cases of which 18 were domestically acquired. Eleven were children under the age of 10. Ten domestic HUS cases belonged to serotype O157: H7.

In 2019, an unusually high number of farms in southern Sweden, 12 in total, were investigated following suspicion of STEC infection. The repeated occurrence of STEC O26 among farms in recent years is notable. This echoes a trend of increasing human O26 cases in Sweden. A nationwide cattle slaughterhouse prevalence study targeting O26 and O157 will be conducted in 2020 and 2021.

Domestic rise for Salmonella
In 2019, 1,993 cases of salmonellosis were reported, compared to 2,040 in 2018. Domestic cases increased from 677 in 2018 to 763 in 2019. Thailand is the top country for travel-associated salmonellosis, although the number has decreased in the past years.

Among domestic cases, the median age was 45 years with a range of 0 to 94, and incidence was highest for children younger than 5 followed by people over 80 years old. The most common serovars from domestic cases were monophasic Salmonella Typhimurium, Enteritidis, and Typhimurium. Around 70 other types were identified in domestic cases.

In July 2019, the County of Dalarna informed the Public Health Agency of Sweden about 15 people with salmonellosis with an epidemiological link to a pizzeria/kebab restaurant. Food analyses identified Salmonella Enteritidis in sliced cucumber and sliced tomatoes as well as on a worktop where food was prepared. Identical strains were found in nine Norwegian patients who had been in Sweden during this time, but it could not be confirmed they had visited the restaurant.

During July through November, 33 people from 12 counties were notified with Salmonella Newport. Most of those sick had eaten a brand of frozen pre-cooked Chinese crayfish, which was recalled by the retail company. Salmonella Newport was detected in samples of crayfish taken by the retailer and in border control.

In early autumn 2019, the county of Jönköping reported an increase in salmonellosis. The outbreak spread nationally, and a case-control study pointed towards small tomatoes being the likely source. In total, 82 cases were identified.

In October 2019, a cluster of Salmonella Mikawasima was identified. Simultaneously, an outbreak alert was launched at the EU level by Public Health England. Epidemiological studies did not identify a suspected food item but pointed towards a source with a short expiry date widely distributed in Europe. In total, 36 cases were identified in 12 counties. Internationally, almost 200 cases were reported.

Record Crypto levels
In 2019, 1,088 cases of cryptosporidiosis were reported. This is the highest incidence since 2004 when it became a notifiable disease. A total of 771 cases were domestic, 304 travel-associated and for 13 there was no information on place of infection. Most of the travel-associated cases were from Portugal closely followed by Spain and Turkey.

In autumn 2019, there was a substantial increase in domestic reported cases of cryptosporidiosis, and five foodborne outbreaks of C. parvum were identified through typing and surveys. A total of 450 of 771 of the annual domestic cases were reported from October to December.

Unpasteurized juice with spinach was identified as the source of infection for most cases. No source of infection was identified for the second most common subtype. Other common subtypes were found in cases that had visited different Christmas buffets in December where fresh kale from four producers in the southern part of Sweden was the probable source of infection.

In May, one patient sought care for abdominal symptoms in Jönköping county. They attended a confirmation reception where 11 to 12 others also reported abdominal symptoms. Four samples were analyzed and were positive for C. parvum. Through surveys, green salad was identified as the probable cause of infection. A smaller outbreak of Cryptosporidium chipmunk genotype I was detected at a pre-school in Stockholm in September. The suspected source of infection was a culture of peas in the yard of the pre-school where red squirrels had been spotted.

Tick-borne encephalitis and Brucella
In a survey in 2019, antibodies to the Tick-borne encephalitis virus (TBEV) were found in four of 108 tested bulk milk samples.

Although most cases acquire the TBE infection via tick bites it can be foodborne. Outbreaks and clusters of cases caused by the consumption of unpasteurized milk products have been described in Baltic, Balkan, and central European countries. The survey showed the virus circulates in the Swedish population of dairy cattle.

In 2019, 14 brucellosis cases were reported, which is within the range seen during the past 10 years. Seven were travel-associated mainly from the Middle East and Horn of Africa regions. Three cases were domestic infections. Seven cases ate unpasteurized milk products, three had consumed the products in Iraq and one person with a domestic infection had eaten unpasteurized cheese purchased in Iraq.

Yersinia at the highest level in a decade
During 2019, 393 Yersinia cases were reported. This is the highest incidence in 10 years. The proportion infected in Sweden increased from around 75 percent in previous years to near 80 percent of cases. Similar to previous years, the incidence was high among children younger than five years.

Two large outbreaks were identified and both mainly included cases in the age group 15 to 39-year-olds. In the first outbreak, an unusual increase of Y. enterocolitica and Y. enterocolitica O3 biotype 4 was identified. Denmark reported a match and in the Danish case-control study, there was a clear link to fresh spinach from a large retail store. A trace-back investigation found a common producer of fresh spinach supplying both the Danish and Swedish markets via different wholesalers. In total, 57 cases were identified and 37 came from Sweden.

Most cases in the second outbreak were reported in May. In total, 30 cases and all isolates formed a cluster within the same type of Yersinia enterocolitica as the first outbreak. However, no source could be identified.

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