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Salmonella in Food Commonly Containing Raw or Lightly Cooked Eggs


Abstract

Eggs are nutritious foods and form an important part of human diet and commonly consumed. Eggs may be contaminated with Salmonella via “vertical transmission” through the ovary of the hen, or “horizontal transmission” through the shell of the egg. In Hong Kong, Salmonella is one of the most common causative agents of food poisoning. Among the confirmed salmonellosis cases recorded by the Department of Health in the past 4 years, more than 40% of them were related to the consumption of eggs or egg products while undercooking or eating raw eggs were the main contributory factors to these cases. The Centre for Food Safety (CFS) and the Consumer Council have conducted a joint study to assess the Salmonella contamination in food commonly containing raw or lightly cooked eggs in the local market and arouse public and trade awareness regarding the safety of these products during production.

Background

2.         Salmonella is a bacterium that can be found in the intestinal tract of man and animals. Salmonella is more commonly found in food of animal origin, including eggs, meat, poultry and raw milk.

3.         Eggs may be contaminated via two different routes: vertical transmission or horizontal transmission. For vertical transmission, Salmonella are introduced from infected reproductive tissues to eggs prior to shell formation while horizontal transmission usually occurs from faecal contamination on the egg shell as the eggs are released via the cloaca, where the excretion of faeces also takes place; also includes contamination through environmental vectors e.g. farmers, pets and rodents.

4.         Even thorough cooking can kill Salmonella effectively, eating raw or undercooked food or ready-to-eat cooked food contaminated with Salmonella may result in salmonellosis.

5.         In Hong Kong, Salmonella is one of the most common causative agents of food poisoning. Symptoms include nausea, fever, abdominal pain, diarrhoea, and vomiting would be developed within 6 - 72 hours (usually 12 - 36 hours) upon the consumption of Salmonella contaminated food. Anyone can be suffered from salmonellosis, however, serious consequences, even death, may be resulted in the elderly, infants and those with impaired immune systems.

The Study

6.         From June to July 2014, the CFS obtained a total of 100 egg-containing ready-to-eat samples from various retail premises and dispatched to the Public Health Laboratory Services Branch of the Centre for Health Protection, Department of Health for Salmonella spp. analysis.

7.         Salmonella was not detected in any samples in the study. This may be due to the study limitations e.g., limited number of samples were included and the samples only focused on specific types of food. Undercooked eggs and egg products and food prepared with raw eggs have both been involved in overseas and local Salmonella food poisoning cases. Eggs formed an important part of our diet and commonly consumed; the risk of contracting salmonellosis is relatively higher if the public frequently consume undercooked eggs and food prepared with raw eggs. Despite of the study result, the public should not take the risk lightly. To ensure food safety, the trade and the public should always maintain good personal and food hygiene.

Advice to public

•    Store shell eggs in a cool and dry place, ideally under refrigeration. Avoid using cracked eggs as they are more likely to be contaminated and thus present a higher health risk.
  Purchase clean and intact shell eggs from reliable premises.
  Observe the expiry date and storage temperature on the package/label of eggs.
  As a general rule, shell eggs need not to be washed.  However, if eggs are soiled with faecal matter, they can be washed. Washed eggs should be used immediately.
  Avoid eating raw or inadequately cooked eggs and egg products, particularly so for the elderly, infants and pregnant women.
  Eggs should be thoroughly cooked until the yolk and white are firm.
   
  Choose pasteurised eggs or egg products or dried egg powder to prepare dishes not requiring heat treatment.

Advice to trade

•    Avoid cross-contamination between raw eggs and other food. The food contacting surface and utensils used for preparation of raw eggs should be cleaned thoroughly.
  Choose pasteurised eggs or egg products or dried egg powder to prepare dishes not requiring heat treatment.
  Avoid using cracked eggs as they are more likely to be contaminated and thus present a higher health risk

More information

8.         The related article is published in the CHOICE MAGAZINE (Issue 457 released on 17 November 2014)(Chinese only)

November 2014
Risk Assessment Section

Centre for Food Safety
Food and Environmental Hygiene Department

 

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Last Revision Date : 17-11-2014