Food Safety Focus Banner

To the main pageNext Article

Food Safety Focus (144th Issue, July 2018) – Incident in Focus

E. coli  O157:H7 in Romaine Lettuce and Ground Meat Products

Reported by Dr. Cherrie NG, Veterinary Officer,
Risk Communication Section,
Centre for Food Safety


In April 2018, the Centre for Food Safety (CFS) announced that import into and sale in Hong Kong of romaine lettuce produced in the State of Arizona (AZ), the United States (US), had been suspended with immediate effect, as the product might have been contaminated with Escherichia coli (E. coli) O157:H7. This article provides information on the cause and symptoms of E. coli  O157:H7 infection and its prevention.

What Happened in this Incident Involving Romaine Lettuce in the US?

As of 28 June 2018, the US Centers for Disease Control and Prevention reported that 210 people from 36 states were infected with the outbreak strain of E. coli  O157:H7. Ninety-six people were hospitalised with five deaths. Eight cases of E. coli O157 infection with a similar genetic fingerprint were also reported in Canada. Investigations indicated that romaine lettuce from the Yuma region of AZ could have been contaminated with Shiga toxin-producing E. coli (STEC) O157:H7 and was the likely source of this outbreak. Multiple establishments were involved and no single farm, processor or distributor was solely responsible for the outbreak. Water samples taken from a canal in the Yuma region were the only matches to the outbreak strain. Investigation in the US continues.

What Causes E. coli  O157:H7 Infection?

E. coli  refer to a large group of bacteria and are commonly found in the lower intestine of warm-blooded animals. Whilst most E. coli are harmless, some, such as STEC, can cause severe foodborne diseases. The most recognised and virulent serotype of STEC is E. coli  O157:H7. It is pathogenic in humans, but usually asymptomatic in animals.

The main reservoir of E. coli  O157:H7 is cattle. Thetransmission to humans is primarily through consuming contaminated foods (e.g. raw/undercooked ground meat products and raw milk). Faecal contamination of food and water, and cross-contamination during food preparation (with beef and other meat products, contaminated surfaces and kitchen utensils) also lead to infection. Further, an increasing number of outbreaks are associated with consuming contaminated fruits and vegetables. Such contamination can be from contact with contaminated manure, contaminated water used for irrigations or washing and worker hygiene throughout the food chain.

What Are the Symptoms of E. coli  O157:H7 Infection?

The symptoms include abdominal cramps and diarrhoea that may in some cases progress to bloody diarrhoea. Vomitting and fever may also occur. Most patients recover within ten days but a small proportion (particularly young children and the elderly), may lead to life-threatening diseases such as haemolytic uraemic syndrome (HUS). HUS is characterised by acute renal failure, haemolytic anaemia and low blood platelets.

How to Prevent E. coli  O157:H7 Infection?

STEC is heat-sensitive, thus, preventative measures for other foodborne infections, such as "cook thoroughly" are also recommended to E. coli O157:H7. Meat may be contaminated with E. coli O157:H7 on the surface from the slaughter process or subsequent handling. When meat is minced then made into ground meat products (e.g. hamburgers), these surface bacteria will be brought into the inner part of the meat. Therefore, ground meat products, in particular, should be thoroughly cooked until brown throughout and the juices run clear. Fruits and vegetables, especially if to be eaten raw, should be washed thoroughly under clean running water. One should wash hands thoroughly with water and soap, particularly before handling food and after using the toilet.

Actions Taken by CFS

In view that romaine lettuce produced in AZ in the US might have been contaminated with E. coli  O157:H7, in addition to the import suspension mentioned earlier, the CFS has urged the trade to stop using and selling the product concerned immediately should they possess it. Besides, the CFS also has enhanced surveillance of romaine lettuce produced in the US at import and retail levels.

Key Points to Note:

  1. Although the primary sources of human E. coli O157:H7 infections are contaminated undercooked ground meat and raw milk, outbreaks associated with fruits and vegetables are increasing.
  2. The symptoms of E. coli O157:H7 infection include abdominal cramps and diarrhoea but a small proportion of patients can develop life-threatening HUS.
  3. Preventative measures for E. coli O157:H7 infections are similar to those recommended for other foodborne diseases (e.g. "cook thoroughly").

Advice to the Trade

Advice to the Public