Prevention and Control of Enterohaemorrhagic Escherichia Coli (EHEC) Infections: Memorandum from a WHO Meeting(*)

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In 1982, Escherichia coli O157:H7 was recognized as a human pathogen for the first time, and since then has been a steadily increasing cause of foodborne illness worldwide. Although the main reservoir of this pathogen appears to be cattle, the dynamics of E. coli O157 in food-producing animals and the environment is not well understood. It is transmitted principally through consumption of contaminated foods, such as raw or undercooked ground meat products and raw milk. Faecal contamination of water and other foods and cross-contamination during food preparation are important routes of infection. Examples of foods implicated in outbreaks of E. coli O157 infection include hamburgers, roast beef, raw milk, unpasteurized apple juice, yoghurt, cheese, fermented sausage, cooked maize, mayonnaise-containing dressings, lettuce, and seed sprouts. The pathogen is relatively tolerant to acid and can survive in fermented foods and fresh vegetable produce. Waterborne transmission has also been reported, both from contaminated drinking-water and from recreational waters. Person-to-person contact is an important mode of transmission, particularly in institutional settings, such as day care centres, nursing homes and hospitals. Direct contact with farm animals and birds carrying the organism is also a recognized source of infection. The role of asymptomatic food handlers in outbreaks is unclear but it may be important in view of the low infectious dose. The range of foods reported as vehicles of transmission and the numerous transmission routes create a major challenge in terms of designing prevention and control strategies.

More recently, there have been unprecedented, large outbreaks of E. coli O157:H7 infection in Japan and Scotland, and outbreaks due to other enterohaemorrhagic E. coli (EHEC) in Australia and Europe. There have also been a significant number of outbreaks in the USA linked to the consumption of contaminated vegetable products, such as lettuce and alfalfa sprouts. The largest ever recall of food on record occurred in the USA in 1997, when about 10 000 tonnes of raw frozen hamburgers were recalled because of suspected contamination by E. coli O157.

In view of the magnitude and severity of recent outbreaks of foodborne diseases caused by E. coli O157:H7, there is an urgent need for all sectors in the food chain to work together to reduce or eliminate the health impact of this hazard. Achieving a significant reduction in the incidence of foodborne disease caused by this pathogen will require the cooperative efforts of public health and environmental health agencies, farmers, animal producers, food processors and caterers, together with research scientists.

Global overview of EHEC infections

During the consultation, participants presented overviews of current national situations with respect to EHEC infections as outlined below.

African Region

Bloody diarrhoea is a major cause of morbidity and mortality among children in African countries, yet the proportion caused by E. coli O157:H7 and other EHEC is largely unknown. In South Africa, for example, infections caused by EHEC are not notifiable and there is very limited information on E. coli O157 infection in animals. Since 1988 three cases of E. coli O157 colitis have been identified in Pretoria, one of which was associated with eating a hamburger from a fast-food outlet. Many cases of haemorrhagic colitis caused by nonmotile E. coli O157 from Swaziland and the adjacent South African provinces of Mpumalanga and KwaZulu-Natal were identified in 1992. Isolates of E. coli O157 were obtained from patients, water, cattle faeces and one sample of cooked maize. An undocumented number of cases of haemolytic uraemic syndrome (HUS) occurred during this outbreak.

Reports of EHEC as a cause of diarrhoea in other African countries are sporadic. In a study of childhood diarrhoea in Nigeria, samples of EHEC were isolated from 5. …