Epidemiological studies and proposed preventive measures in the fight against human salmonellosis

A large number of countries annually report high numbers of Salmonella infections in man. Since it is estimated that these reported cases only represent 1 to 10% of the real incidence of this disease, it must be concluded that human salmonellosis is a serious problem all over the world. The major source for human salmonellosis is caused by farm animals, which may frequently be intestinal carriers of the organism. Particularly pigs and poultry are incriminated in this respect, and, to a lesser degree, cattle and sheep. Because generally no symptoms of disease can be observed, these animals usually pass veterinary slaughterhouse inspection without restrictions. During slaughter however, intestinal material, often containing Salmonella bacteria, pollutes the surface of carcasses, which in later stages may lead to extensive Salmonella contamination of meat and meat products. Additionally, milk may also be contaminated by faecal material during collection, while eggs may be externally contaminated by faecal material or internally infected by way of transovarial transmission. Cross-contamination in slaughterhouses, in butchers' shops and in the kitchen may add to the problem. Human infection occurs when animal products are improperly handled during final preparation. This may happen at home, but also in large kitchens of restaurants, hospitals, institutions and factories. In most instances infection is related to cross-contamination from meat to foods that are to be consumed without further treatment, such as bread, salads and fruits, to improper heating of the animal products themselves, as for instance with eggs, or even to the consumption of raw animal products, as may be the case with meat and milk. The faecal excretion of Salmonella by human patients, wild and domesticated animal carriers, as well as the disposal of slaughter offal, sludge, slurry and manure contributes to an overall Salmonella spread in the environment. This may lead, by way of contamination of surface waters and colonisation of birds, rodents and insects, to the contamination of animal feeds or directly contribute to the re-colonisation of farm animals. In order to solve the problem of human salmonellosis, measures should be taken simultaneously on several levels. Since there are so many transmission ways, particularly in the environment and on the farm, isolated actions, such as the decontamination of animal feed, will never give lasting results. Likewise, the sole responsibility for the problem should never lie with the consumer. An integrated approach should involve measures in the field of Salmonella-free production of slaughter animals, improvement of hygiene in slaughterhouses and shops, possibly combined with decontamination of meat, education of all people involved in the final preparation of foodstuffs and the hygienic disposal or processing of offal, sludge, slurry, manure and other Salmonella-contaminated wastes.