Listeria and listeriosis, relatively rare but not insignificant food safety and public health problems. An in-depth study to follow.
Listeriosis, a rare but fearsome disease
Listeria monocytogenes
, according to the World Health Organization (
WHO
/WHO, 2015), is an exclusively foodborne pathogen. (1) Listeriosis in the EU has a very low incidence, currently close to 0.5 cases per 100,000 population. In comparison, campylobacteriosis and salmonellosis in the EU have much higher incidences, 246,000 and 94,500 cases per 100,000 population, respectively (EFSA and ECDC, 2017). Listeriosis, however, is unfortunately one of the most dreaded foodborne diseases because of its high mortality rate.
Listeriosis-unlike other food-bornediseases-rarely escapes clinical diagnosis, especially in invasive cases. In 2016 in the EU, the hospitalization rate reached 97.7 percent, mortality 16.2 percent (EFSA, 2017). The vast majority of infections (16-27%) unfortunately occur in pregnant women, with even severe repercussions on gestation. L. monocytogenes is indeed one of the most common causes of meningitis in infants (Ronald et al., 2011). (2)
Listeriosis, how it manifests itself
Listeriosis can manifest as acute febrile gastroenteritis. In healthy individuals, this follows the ingestion of foods where L. monocytogenes has reached very high values (greater than one million bacteria per gram). A level of contamination that is rare on foods just placed on the market and rather tends to occur after prolonged storage (albeit at the correct temperature, within 4° C).
Invasive or systemic listeriosis has a much more severe course. It typically affects preschool children, the elderly, and immunocompromised individuals due to concomitant diseases or immunosuppressive therapies (Goulet et al., 2012). And it is characterized by septicemia, meningitis, and meningoencephalitis, which occur after long incubation (up to 90 days).
In pregnant women, listeriosis does not initially appear in full severity, manifesting rather as gastroenteritis or flu-like syndrome. However, possible trans-placental transmission can cause very serious consequences to the fetus. Mortality, premature births, births of infants with meningitis or septicemia (Gianfranceschi et al., 2017).
Listeria, foods at risk
Ready-to-eat foods, so-called RTE(Ready-To-Eat foods), are those most at risk. Also because they do not require treatments-such as cooking or heating-that might be able to eliminate the bacteria.
Listeria risk is needed especially on ready-to-eat foods with a long shelf life (>15 days), subject to the cold chain and conditions that facilitate the growth of the bacterium. In cases of products with high water activity and/or pH close to neutrality, such as soft cheeses, blue cheeses, smoked fish products.
The ability of the pathogen to multiply during storage at refrigeration temperature (+4° C) implies that a purely low number of bacteria in the initial stage can reach a high numerical value, in the case of prolonged storage, such that it can cause infection in the consumer.
Listeriosis, how to prevent the risks
Consumers can be advised to prevent risk through some simple steps:
– do not buy ‘Ready-To-Eat‘ (RTE) products with long shelf-life near the expiration date (have spent many days at temperature permissive to the development of L. monocytogenes),
–
maintain the cold chain
carefully, storing ready-to-eat foods always in the refrigerator,
–
do not store RTE products in the refrigerator for a long time, instead consuming them immediately after purchase,
–
reheat RTE foods such as frankfurters and delicatessen products to be eaten hot (e.g., rice salads, pasta salads, preparations with meat, fish, or vegetables) to the point of steam release,
–
thaw
frozen and deep-frozen products at refrigeration temperatures rather than at elevated temperatures (e.g., 20°C), which allow more rapid development of listeria, where present. Cook products after thawing,
– do not give YOPIs(Young, Old, Pregnant, Immunocompromised) the products that traditionally present the greatest danger of contamination and development of L. monocytogenes. Namely, children, the elderly, pregnant women, and the immuno-compromised.
Silvia Bonardi and Dario Dongo
Notes
(1) Gianfranceschi M, De Medici D, Fiore A, Pontello M, Liguori G, Blasi G, Gattuso A. Listeria monocytogenes. Istituto Superiore di Sanità ISTISAN Report 17/34, 2017: 31-36
(2) Fortunately, targeted and timely antibiotic treatment can counteract the disease. And, in the case of pregnant women, also prevent transmission of the infection to the embryo or fetus. Cf. EFSA, The European Union summary report on antimicrobial resistance in zoonotic and indicator bacteria from humans, animals and food in 2015. EFSA Journal 2017a;15(2):4694 212pp
Bibliographic sources.
European Food Safety Authority (EFSA), European Centre for Disease Prevention and Control (ECDC) (2017) The European Union summary report on trends and sources of zoonoses, zoonotic agents and food-borne outbreaks in 2016. EFSA Journal 15 (12):5077 [Online December 12, 2017].
Goulet V, Hebert M, Hedberg C, Laurent E, Vaillant V, De Valk H, et al. Incidence of listeriosis and related mortality among groups at risk of acquiring listeriosis. Clin Infect Dis 2012;54: 652-60.
Ronald FL. Sobel JD, Mazaki-Tovi S, Kusanovic J P, Vaisbuch E, Kim SK, Uldbjerg N, Romero R. Listeriosis in pregnancy: a systematic review. Journal of perinatal medicine 2011; 39: 227-236.
WHO. WHO estimates of the global burden of foodborne diseases. I. Foodborne diseases burden epidemiology reference group 2007-2015.. Geneva: World Health Organization; 2015.
Graduated in Veterinary Medicine and Specialist in Inspection of Food of Animal Origin and in Veterinary Public Health, she is Professor of Inspection and Control of Food of Animal Origin at the University of Parma.
Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.
