|Fact sheet No 124: Emerging Foodborne Diseases - Revised November 1996 (WHO, 1996, 3 p.)|
|Why Do Foodborne Diseases Emerge?|
Some foodborne diseases are well recognized, but are considered emerging because they have recently become more common. For example, outbeaks of salmonellosis have been reported for decades, but within the past 20 years the disease has increased in incidence on many continents. In the Western hemisphere and in Europe, Salmonella serotype Enteritidis (SE) has become the predominant strain. Investigations of SE outbreaks indicate that its emergence is largely related to consumption of poultry or eggs.
However, in 1994, there was a nationwide outbreak of salmonellosis in the United States as a result of contamination of pasteurized ice cream during transport in lorries that had previously carried nonpasteurized liquid eggs containing Salmonella enteritidis. It is estimated that 224,000 persons were affected by the outbreak.
While cholera has devastated much of Asia and Africa for years, its introduction for the first time in almost a century into the Western hemisphere in 1991 makes it another example of an infectious disease that is both well-recognized and emerging. While cholera is often waterborne, many foods also transmit infection. In Latin America, ice and raw or underprocessed seafood are important epidemiological pathways for cholera transmission.
Other foodborne pathogens are considered emerging because they are new microorganisms or because the role of food in their transmission has been recognized only recently. Infection with Escherichia coli serotype O157:H7 (E. coli) was first described in 1982. Subsequently, it has emerged rapidly as a major cause of bloody diarrhoea and acute renal failure. The infection is sometimes fatal, particularly in children. Outbreaks of infection, generally associated with beef, have been reported in Australia, Canada, Japan, United States, in various European countries, and in southern Africa.
In 1996, an outbreak of Escherichia coli O157:H7 in Japan affected over 6,300 school children and resulted in 2 deaths. This is the largest outbreak ever recorded for this pathogen.
Listeria monocytogenes (Lm) is considered emerging because the role of food in its transmission has only recently been recognized. In pregnant women, infections with Lm can cause abortion and stillbirth, and in infants and persons with a weakened immune system it may lead to septicemia (blood poisoning) and meningitis. The disease is most often associated with consumption of foods such as soft cheese and processed meat products that are kept refrigerated for a long time because Lm can grow at low temperatures. Outbreaks of listeriosis have been reported from many countries, including Australia, Switzerland and the United States. Two consecutive outbreaks of Listeria monocytogenes in France in 1992 and 1993 were caused by contaminated pork tongue and potted pork.
Foodborne trematodes are also emerging as a serious public health problem, especially in south-east Asia, in part due to a combination of increased aquaculture production, often under unsanitary conditions, and of underprocessing of aquaculture products during their preparation. Foodborne trematodes can cause acute liver disease, and may lead to liver cancer.