Listeria and listeriosis, relatively rare but not negligible food safety and public health problems. An in-depth study to follow.
Listeriosis, a rare but fearful disease
Listeria monocytogenes, according to the World Health Organization (WHO/ WHO, 2015), is a pathogen with exclusive food transmission. (1) Listeriosis in the EU has a very low incidence, currently close to 0,5 cases per 100.000 inhabitants. In comparison, campylobacteriosis and salmonellosis in the EU have much higher incidences, respectively of 246.000 and 94.500 cases per 100.000 population (EFSA and ECDC, 2017). Unfortunately, however, listeriosis is one of the most fearful food-borne diseases, due to its high mortality.
listeriosi - unlike other food-derived diseases (food-borne disease) - rarely escapes clinical diagnosis, especially in invasive cases. In 2016 in the EU, the hospitalization rate reached 97,7%, mortality 16,2% (EFSA, 2017). Unfortunately, the majority of infections (16-27%) occur in pregnant women, with even severe repercussions on gestation. L. monocytogenes it is indeed one of the most common causes of meningitis in newborns (Ronald et al., 2011). (2)
Listeriosis, how it manifests itself
Listeriosis can manifest itself such as acute febrile gastroenteritis. In healthy subjects, this results from the ingestion of food where L. monocytogenes has reached very high values (over 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 it 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). It is characterized by septicemias, meningitis and meningo-encephalitis, which occur after long incubation (up to 90 days).
In pregnant women, listeriosis does not initially appear in all its severity, rather manifesting itself as gastroenteritis or flu-like syndrome. However, any trans-placental transmission can cause very serious consequences for the fetus. Mortality, premature births, births of newborns 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 - which may be able to eliminate the bacterium.
The Listeria risk occurs above all 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 the cases of products with high water activity and / or pH close to neutral, such as soft cheeses, blue cheeses, smoked fish products.
The capacity of the pathogen multiplying during storage at refrigeration temperature (+ 4 ° C) means that a low number of bacteria in the initial phase can reach a high numerical value, in the case of prolonged storage, such as to cause infection in the consumer.
Listeriosis, how to prevent risks
Consumers can be suggested risk prevention, thanks to some simple measures:
• not buy products 'Ready-To-Eat'(RTE) long shelf life near the expiration date (they spent many days at permissive temperatures developing L. monocytogenes),
• maintain the cold chain carefully, always keeping ready-to-eat foods in the refrigerator,
• do not store RTE products in the refrigerator for a long time, instead consuming them immediately after purchase,
• heat RTE foods such as würstel and gastronomy products to be consumed hot (e.g. rice salads, pasta salads, preparations with meat, fish or vegetables) up to the emission of steam,
• defrost frozen and deep-frozen products at refrigeration temperature rather than at high temperatures (e.g. 20 ° C), which allow faster development of listeria, where present. Cook the products after defrosting,
• do not administer to the YOPI (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 immuno-compromised ones.
Silvia Bonardi and Dario Dongo
(1) Gianfranceschi M, De Medici D, Fiore A, Pontello M, Liguori G, Blasi G, Gattuso A. Listeria monocytogenes. ISTISAN Institute of Health Report 17/34, 2017: 31-36
(2) Fortunately, timely and targeted antibiotic treatment can counteract the disease. And, in the case of pregnant women, also prevent the transmission of the infection to the embryo or fetus. See 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
European Food Safety Authority (EFSA), European Center 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 JP, Vaisbuch E, Kim SK, Uldbjerg N, Romero R. Listeriosis in pregnancy: a systematic review. Journal of perinatal medicine 2011; 39:227-236.
WHO extension. WHO estimates of the global burden of foodborne diseases. I. Foodborne diseases burden epidemiology reference group 2007-2015. Geneva: World Health Organization; 2015.