Despite a drop in reported Listeria infections in 2019 the number of outbreaks remained similar to previous years, according to Public Health England (PHE).

A total of 142 cases of listeriosis were reported in England and Wales compared to 157 the year before. This represents an 11.5 percent decline versus the average number in the preceding six years.

There were four outbreaks of listeriosis investigated in England in 2019. For two of them, with three and two clinical cases, the source of infection was unknown. One international outbreak involving five people from 2018 to 2019 was linked to pork products of Romanian origin.

Listeria sandwich outbreak
The other involved prepacked sandwiches served in National Health Service (NHS) hospitals. This outbreak was detected in North West England after two patients were infected with Listeria monocytogenes in the same hospital and subsequently died. Other cases were later identified across seven NHS Trusts using whole genome sequencing (WGS).

Between May 16 and June 14, 2019, nine confirmed cases associated with the outbreak were identified and seven people died. All nine received care at hospitals supplied by The Good Food Chain, the implicated sandwich manufacturer. Consumption of prepacked sandwiches from this company was confirmed for eight people.

Listeria monocytogenes isolates from chicken sandwiches and cooked chicken samples supplied by the sandwich manufacturer and a meat producer called North Country Cooked Meats were confirmed as the outbreak strain by WGS analysis.

May was the peak month for listeriosis reporting in 2019, with the outbreak influencing this result. In 2017 and 2018 numbers peaked in July, with no outbreaks in those months.

Overall, age-specific incidence rates were highest in people 80 years and over. Of 26 cases in the 10 to 19, 20 to 29 and 30 to 39 age groups, 24 were female, of which 19 were associated with pregnancy.

Severe outcome
The outcome of listeriosis during pregnancy remains severe with a third of infections resulting in miscarriages or stillbirths. In 2019, 25, which is less than a fifth of cases, were associated with pregnancy which was comparable to previous years. Amongst pregnancy-associated cases, 64 percent of pregnancies resulted in live births and 36 percent in stillbirth or miscarriage.

There were 23 deaths among 117 non-pregnancy cases, compared to an average of 43 deaths among reported cases from 2013 to 2018.

Of the 23 fatalities, 15 were known to have listeriosis recorded as a cause on the death certificate. This represented a fatality rate of 12.8 percent, compared to 8.5 percent in the previous year.

London had the highest incidence rate with 35 infections whilst the East of England had the lowest with seven patients. Wales recorded three cases.

Incidence of listeriosis was lower in men than women, but reports among men aged 60 to 69 were seven times higher than women in this age range.

Five incidents were investigated involving sporadic cases in 2019 that were microbiologically linked to food or a food environment by detection of the same strain of Listeria monocytogenes by whole genome sequencing.

“As a predominantly foodborne infection, this severe disease is largely preventable. It remains imperative that sporadic cases of illness and clusters of disease continue to be monitored and investigated to inform the continued risk assessment of the food chain,” according to the report.

About Listeria infections
Food contaminated with Listeria monocytogenes may not look or smell spoiled but can still cause serious and sometimes life-threatening infections. People with symptoms of Listeria infection should seek medical treatment and tell their doctors about any possible Listeria exposure.

It can take up to 70 days after exposure to Listeria for symptoms of listeriosis to develop.

Symptoms of Listeria infection can include vomiting, nausea, persistent fever, muscle aches, severe headache, and neck stiffness. Specific laboratory tests are required to diagnose Listeria infections, which can mimic other illnesses.

Pregnant women, the elderly, young children, and people such as cancer patients who have weakened immune systems are particularly at risk of serious illnesses, life-threatening infections, and other complications.

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