Whole genome sequencing helped identify concurrent outbreaks of a rare Salmonella serotype in Germany in 2017, according to a study.
Whole genome sequencing (WGS) of Salmonella Kottbus isolates revealed three co-circulating clusters in the country between June and August 2017. A total of 69 infections were identified in 13 German states. Median age was 55 years with a range of 0 to 91 and 55 percent were female. Salmonella Kottbus is a rare serotype with usually three to four reports of patients per month.
Researchers investigated the outbreak with WGS and a case-control study. Findings were published in the journal Epidemiology and Infection. Forty-six isolates from 69 cases were subtyped. Three WGS clusters were identified as cluster 1, cluster 2 and cluster 3. Compared to controls, cluster 1 cases more frequently ate raw smoked ham bought at a supermarket chain. All four cluster 2 cases interviewed had eaten quail eggs.
Large outbreak linked to ham
Thirty-six patients belonged to the largest outbreak cluster, called cluster 1. Patients were also identified in Denmark and the U.K. In Germany, this strain had not previously been detected in humans.
Of all interviewed confirmed patients, 82 percent of infections could be explained by raw smoked ham. A brand of ham bought from one supermarket chain was identified by nine of 10 cases asked.
One patient from the U.K. with symptom onset in May 2017 without travel history had handled and consumed raw pork. Of four patients from Denmark with symptom onset in April to September, three were interviewed and had bought food in German supermarkets in Denmark. Two travelled to Germany in the week before symptom onset and one consumed ham bought in Northern Germany from the supermarket chain.
The matching isolate from pork for animal feed in April 2017 before the outbreak supports ham as the likely vehicle, according to the report, even if a link between the isolate and ham could not be established. Salmonella Kottbus was not detected in food samples, but they were collected late during the outbreak investigation. By September 2017, the number of reports fell to the usual number.
The ham producer presented negative microbiological results from internal controls at the beginning of August 2017.
Small outbreak traced to quail eggs
Researchers said it was possible that other pork products, especially if consumed raw, contributed to the outbreak. Two of the three cases with no or uncertain ham consumption in the case-control study had eaten raw ground meat, potentially containing pork.
Although consumption of raw minced meat may explain additional cases and was more commonly reported by cases than controls in the case-control study, it was not statistically significant and the exposure only explained 29 percent of cases. As both products came from the same food source, it remains unclear if raw minced meat additionally contributed to the cluster 1 outbreak.
Quail eggs were the likely source for the smaller second cluster of five cases, called cluster 2. All four people interviewed reported having them. This was disproportionately high, especially as only 1 percent of German adults in a survey in 2017 reported quail egg consumption in the past week.
Two cases reported eating the eggs raw or soft-boiled. Quail eggs were bought at two different supermarket chains but a common origin could not be excluded. Cases said they ate quail eggs for health reasons, as a nourishing food or because of chicken egg allergies.
Of five confirmed cluster 2 cases, four were female with a median age of 58 and were exposed in five states. All three confirmed cluster 3 cases were male, aged 31 to 71 and lived in Hesse. No common food was identified for two interviewed cluster 3 cases.
Food consumption data in outbreaks
Meanwhile, another study in the same journal, presents a food consumption survey in those older than 18 years in Germany to get data on the frequency of consuming items that caused foodborne outbreaks in the past, such as unheated sprouts and unpasteurized milk.
A total of 1,010 telephone interviews in autumn 2017 asked about the consumption of 95 food items in thevseven-day period before the interview. The study’s purpose was to have food consumption data available for future foodborne disease outbreak investigations to speed them up.
Six high risk items were consumed by 6 to 16 percent of the general population, despite publicly available recommendations on health risks. These were raw ground pork; Teewurst (a spreadable sausage-containing raw pork); unpasteurized milk without heating; items prepared with raw eggs; unheated sprouts or seedlings, and frozen berries with no heating prior to eating.
About 370 foodborne outbreaks in Germany were reported annually to the Robert Koch Institute between 2014 and 2018 through the routine surveillance system. They caused about 1,700 recorded gastrointestinal infections per year. On average, about 85 percent of foodborne outbreaks in Germany were small, at less than five cases, and about 50 percent were in private homes.
Researchers used past outbreak investigations to see if the food consumption data would have been helpful. In these outbreaks, results from the survey would have shown consumption of the item that caused the outbreak was lower in the general population than the group of case-patients. This information would have helped direct the investigation toward the causative food vehicle earlier, according to the report.
Data may not be helpful in investigations of outbreaks among certain groups such as young children or the elderly, if it is in a certain region of Germany, where consumption patterns may differ or an investigation of outbreaks caused by pathogens with a much longer or shorter incubation period than seven days, which was the timeframe interviewees were asked about.
Results from the food consumption survey were comparable to data from control persons in case-control studies conducted during past disease outbreak investigations.
“We consider our survey an additional helpful tool that will allow comparison with food consumption data from case-patients obtained in exploratory, hypothesis-generating interviews early on in outbreak investigations, and which may assist in forming hypotheses regarding associations of illnesses with suspected food vehicles,” said researchers.
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