Salmonella is the top pathogen on the list of European food and feed alerts. This is according to the 2017 annual report of the Rapid Alert System on Food and Feed(RASFF). (1) An in-depth study, ABC.
Salmonella, not one but 2600 pathogens
Salmonella
is an extraordinarily widespread enterobacteriaceae, responsible for outbreaks as well as isolated cases of gastroenteric infections in both humans and animals. Its treatment is complex, as more than 2600 serovars of Salmonella(Salmonella Typhimurium, Enteritidis, Infantis, etc.) are known. And also numerous animal species can become infected and transmit the microorganism to humans.
Typhoid, or typhoid fever, a serious disease characteristic of low hygiene areas, in turn belongs to the exclusively ‘human’ salmonellae(Typhi and Paratyphi A). Which, unlike zoonoses, are transmitted exclusively between humans.
Febrile gastroenteritis by
Salmonella
on the other hand, is a zoonotic disease, as the microorganisms colonize the intestinal tract of a wide variety of animals:
- Pets (dogs, cats, and small rodents, e.g., hamsters),
- livestock (chickens, turkeys, pigs, cattle and others),
- mammals and wild birds,
- Cold-blooded animals (such as turtles and snakes).
Transmission to humans can therefore occur either by direct contact with tank animals (which eliminate the microorganism with feces) or by indirect contact. Namely, by ingestion of Salmonella-contaminated food.
Salmonellosis, the disease
Salmonellosis, a gastroenteritis, is considered a ‘self-limiting’ disease. Because its symptoms (fever, nausea, vomiting, diarrhea) may disappear even without therapeutic treatment. In very young children, the elderly, and immune-depressed persons, however, salmonellosis can take a more severe, systemic course.
Variable clinical aspects, ranging from moderate to severe, also affect the number of disease case reports. Salmonellosis-despite the fact that it has been the second-largest notified zoonosis in Europe for years-is indeed greatly underreported. Precisely because of the frequent occurrence of cases that do not require hospitalization of the patient.
Salmonella, in which foods it can be found
The pathogenic microorganism, through fecal excretion of animals, can contaminate:
- meats, during the slaughter process,
- milk, during milking,
- fruits and vegetables, as a result of fertigation practices adopted in agriculture. Or due to the use of non-potable water in the washing steps,
- eggs, if the laying hen is infected at the ovarian level. (2)
The most frequently contaminated foods include poultry meat (chicken and turkey), followed by pork. One element of risk in this area is the use of pork as an ingredient in products intended for consumption without prior cooking (e.g., sausages and lightly seasoned salami), where
Salmonella
can easily remain viable.
Eggs may pose a danger only when consumed raw or used without prior cooking to make sauces (e.g., mayonnaise), creams (e.g., eggnog) or other preparations (e.g., tartare). (3) Keeping the preparations at room temperature, moreover, promotes the multiplication of Salmonella, which is usually present in low cell numbers in the raw egg.
Spices can in turn cause Salmonella toxins. In all cases where they, in their countries of origin, are dried on the ground or otherwise exposed to possible contamination from animal and environmental sources. The bacterium’s resistance to drying, even for long periods, then promotes its permanence.
Salmonella, how to inactivate the bacterium
A temperature of 70°C is always necessary to ensure complete inactivation of the pathogenic bacteria. Thus, one can mitigate the risk, provided:
1–provide for the proper cooking of foods, including their innermost parts. Therefore, cooking must be done carefully and requires special care in some of its methods, such as barbecue, which do not always guarantee the stated goal,
2-keep all tools separate (e.g. cutting boards, knives and forks, plates, etc.) used in the kitchen to manipulate products before cooking. The use of such tools for foods for the table (e.g., for sectioning, storing, or serving the same cooked foods, or other foods intended for raw consumption, such as vegetables) may result in their contamination.
Toxic infection, moreover, is not automatic. In fact, it occurs when Salmonella multiplies and reaches a rather high infectious dose (close to or exceeding one million cells). Only children, the elderly and other at-risk groups can contract the disease with a lower infectious dose.
And the high number of bacteria needed to trigger salmonellosis is achieved as a result of active multiplication of Salmonella. This occurs when contaminated food is stored not at refrigeration temperature (0 – 4°C), but at room temperature for several hours.
The cold chain therefore hinders the development of bacteria, whose growth range is between 5.2°C and 46°C. Freezing is not suitable for inactivating the pathogen, which can remain viable and grow if foods are thawed and kept at temperatures above 4°C.
Common disinfectants (e.g., sodium hypochlorite) used for food hygiene are suitable for inactivating the bacterium. So is cooking, to at least 70°C, and pasteurization of milk to 72°C.
Salmonellosis, theABC for reducing risks
The ABCs of reducing the risk of contracting-or causing others to contract-foodborne salmonellosis, to follow:
A) Hygiene of tools used in the kitchen and hand hygiene after handling risky products (meat and eggs especially). For the specific purpose of preventing cross-contamination between Salmonella-contaminated products and uncontaminated products,
B) Washing and disinfection of vegetables,
C ) Complete cooking (
>
70°C) of risk products,
D) Storage of ready-to-eat products at refrigeration temperature (0-4°C). (5)
It is also good practice not to feed raw products (eggs, milk, meat, fresh sausages and salami, shellfish) that may contain viable pathogenic microorganisms to children and the most vulnerable (6).
Silvia Bonardi and Dario Dongo
Notes
(1) Cf. https://ec.europa.eu/food/sites/food/files/safety/docs/rasff_annual_report_2017.pdf
(2) This occurs in the case of S. Enteritidis. In such a case, eggs are laid whose yolk, which is the egg cell of the laying hen, is contaminated with salmonella
(3) Precisely in order to mitigate the risks of salmonella contamination of products, most food business operators use pasteurized egg products instead of fresh eggs in the preparation of creams and sauces
(4) Indispensable, it goes without saying, the boiling of raw milk, before its consumption
(5) Strictly maintaining the cold chain is also crucial to prevent the multiplication of
Listeria
, as we have already highlighted at https://www.greatitalianfoodtrade.it/salute/listeria-e-listeriosi-un-approfondimento
(6) YOPI(Young, Old, Pregnant, Immunocompromised)
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.
