Food Safety Focus (3rd Issue, October 2006) – Incident in Focus

E. coli O157:H7 Outbreak Associated with Bagged Fresh Spinach in the US

Reported by Mr. Arthur YAU, Scientific Officer,
Risk Communication Section, Centre for Food Safety

Summary of Incident

On 14 September 2006, the US Food and Drug Administration (FDA) advised consumers not to consume bagged fresh spinach in response to an outbreak of E. coli O157:H7 that caused one death and multiple hospitalisations in multiple states. Upon learning the incident, the Centre for Food Safety (CFS) immediately advised local consumers not to consume the type of product from the US. The CFS also contacted the US Consulate General and requested that the export of bagged fresh spinach products from the US to Hong Kong be temporarily suspended. Local retailers and importers were also asked to stop import and sale of bagged spinach products from the US. The FDA subsequently issued more updates on the issue. It stated that the affected spinach was traced back to Natural Selection Food LLC (NS Food) of San Juan Bautista, California.

The FDA also reminded the public that NS Food had recalled all spinach products under multiple brand names with a date code of October 1 or earlier. There had been five other recalls from different companies because they used NS Food's spinach.

What is E. coli O157:H7?

E. coli O157:H7 is a strain of Escherichia coli that is most commonly found in cattle, but also found in the intestines of humans and mammals like deer. This pathogenic E. coli strain can produce potent toxins called Shiga toxin 1 and 2. Affected people may develop gastro-intestinal symptoms that include severe watery diarrhoea, bloody diarrhoea, fever, abdominal cramps or vomiting. The incubation period ranges from 1-10 days (median 3-4 days). About 8% of the patients may develop haemolytic uraemic syndrome (HUS), which is characterised by acute kidney failure. Children under five years old have a higher risk of developing complications such as HUS. Some 1-5% of cases of E. coli O157:H7 infection may die. Although recurring outbreaks of E. coli O157:H7 as a result of food contamination occur overseas, such infections are uncommon in Hong Kong and local cases appeared sporadically. From 1998 to 2005, the Centre for Health Protection of the Department of Health recorded six sporadic human infections of E. coli O157:H7, including one imported case. One of them presented as HUS. As of September 2006, no case of E. coli O157:H7 infection was reported in 2006.

The CFS took samples of ready-to-eat (RTE) food for E. coli O157:H7 examination. From 2004 to June 2006, 585 samples were taken and all results were satisfactory. (Table 1)

Table 1: Ready-to-eat food samples taken for E. coli O157:H7 examination

Source: Centre for Food Safety, Hong Kong

Common Source of Infection

Food and water can be contaminated with E. coli O157:H7 due to contact with cattle faeces. Contamination of agricultural products can occur in the field and meat products in the abattoir. Undercooked and raw foods, such as minced beef, hamburgers, unpasteurized dairy products, vegetables and alfalfa sprouts etc. are of particular concern. Consumption of undercooked or raw food may pose a higher risk of illness as only a small number of the bacteria are needed to cause illness. On the other hand, cooking is effective in killing the bacteria and preventing illness. Furthermore, good personal hygiene and proper food handling techniques will minimise the chance of transmitting this bacteria via the faecal-oral route.

Advice to the Trade

Members of the trade should ensure that they obtain vegetables for raw consumption from reliable sources and that the vegetables are fit for human consumption. Fresh vegetables for raw consumption should be thoroughly washed under clean running tap water.

Advice to the Public

When washing vegetables, the outer leaves from vegetables such as lettuce and cabbage should be discarded prior to washing. They should then be immersed in water for an hour and washed thoroughly with clean running water to remove surface contamination.

People at a higher risk (i.e. young children, elderly people, pregnant women and persons with weakened immune systems) should avoid eating food containing raw vegetables (e.g. salad, coleslaw, pickled vegetables etc.). Vegetables should be thoroughly washed and cooked before consumption in order to reduce the likelihood of disease. It should be noted that thorough washing alone may not be able to remove all the microbiological contamination. Thorough cooking is an effective way to ensure food safety.

Further Information

For readers who are interested in learning more about the incident, please visit the following web pages for further information. *

• US FDA "Spinach and E. coli Outbreak" *
• Risk in Brief - Microbiological Food Safety of Raw Vegetables Intended for Human Consumption
• Microbiological Risk Assessment - Salads