Hong Kong Institute of Medical Laboratory Sciences Ltd.

The International Association of Medical Laboratory Technologists (IAMLT)

Biomedical Laboratory Science Day, April 15th 2002

Biomedical Science - The Key to the Diagnosis of Food and Water-borne Diseases

Food and Water-Borne Diseases

Poor sanitation, faulty plumbing, the use of human excrement as fertilizer, and unclean food handling make food and water borne diseases common diseases.

While diarrhoea can be related to many factors, including change in diet, it is often the result of an infection with one of a variety of organisms (viral, bacterial, or parasitic).

Quite a few disease, including hepatitis A, cholera and typhoid fever, are transmitted by unsanitary food handling procedures and contaminated water. Food and beverage precautions are essential in order to reduce chance of illness.

Hepatitis A
Hepatitis A is a virus that is spread by contaminated food, drinks or water. It is one of the most common serious health problems in travellers for which there is a vaccine. Symptoms of hepatitis A may include fever, fatigue, loss of appetite, nausea and jaundice.

Although hepatitis A occurs worldwide, it is most common in developing countries due to poor sanitary conditions. Hepatitis A vaccine gives a very high level of protection and is recommended for travellers going to risk areas.

Cholera is a bacterial disease that may cause severe diarrhoea and dehydration. The best prevention is strict water and food precautions and good hand-washing. The risk of cholera is very low for most travellers. People working in high-risk situations (e.g. health care, refugee camps) or isolated remote areas may benefit from oral cholera vaccine.

Typhoid Fever
Typhoid fever is a bacterial illness that is spread by contaminated food and water. Symptoms may include headache prolonged high fever, loss of appetite, diarrhoea or constipation and rash. It is a serious illness that may last several weeks and if untreated can be fatal. Typhoid vaccine is recommended for people travellng to areas where sanitation is poor and incidence of the disease is high.

Diagnostic analyses of enteropathogenic organisms
Laboratories of appropriate standards to do bacterial analyses to diagnoses water and food-borne illnesses routinely identify Salmonella, Shigella, Campylobacter and E.coli O157:H7. Many laboratories have the abilities to test for organisms like Yersinia enterocolitica and enteropathogenic Vibrio and other rare organisms, when suspicions arise of infections caused by them. Identification is based on biochemical, serological and genetic characteristics of the organisms.

Susceptibility testing of those organisms is important, as resistance to antimicrobial agents is increasing at alarming rate.

Food and water-borne diseases caused by ova and parasites are serious problems in many developing countries and not uncommon in developing countries. Identification is mainly based on microscopic characteristics of the organisms.

The vast majority of epidemics of acute non-bacterial gastroenteritis are attributable to Calici viruses. Diagnostic analyses are done using molecular techniques.

Diagnostic analyses of pathogens that cause other diseases than gastroenteritis
Many organisms that are the cause of severe diseases, other than gastroenteritis, are food and water-borne. The risk of infection is relative to the hygienic status in the area, thus higher in developing countries where diagnostic analyses may also be lacking. Where the quality standards are appropriate, different methods of diagnostic analyses are selected for different organisms. Selection of samples is also based on the suspected organisms. Examples of organisms of this kind are: - Listeria monocytogenes, hepatitis A virus and polio virus.

Prevention of food and water-borne diseases

The primary strategy in preventing diarrhoea is the avoidance of food and water contaminated with faecal pathogens.

Water Preparation
Tap water may be contaminated unless it is known to be safe; i.e., potential pathogens are removed or inactivated. Drinking bottled water may be the best advice in much of the world, but may not be practical in many instances. The preferred method of water disinfection is to boil it for 3 minutes. This is adequate with even heavily contaminated water.

Food Preparation
In parts of the world, foods purchased or served in restaurants and homes may be contaminated. Serving contaminated foods can easily be prevented by safe cooking and storage methods.

Fresh Fruit and Vegetables: Vegetables may have been fertilized with night soil (human waste), handled by several people, or washed with unclean water. Thorough cooking of vegetables inactivates pathogens but destroys some important nutrients.
Fruits and vegetables that can be peeled are safe once peeled. Any fruits or vegetables that are not or cannot be peeled should be washed in clean water prior to consumption.

Meat preparation: All meats should be cooed thoroughly. Adequate cooking will prevent parasitic (trichinosis and tapeworm) and bacterial infections.

Milk products: Bring all fresh (unpasteurised) milk to boil before consuming. Avoid eating fresh cultured dairy products (such as yoghurt) since there is no way of pasteurising it.

Canned foods are generally safe.

Freezing does not disinfect food.

Food should be eaten immediately after cooking if appropriate cool storage is not available. Delay can allow bacteria to multiply again, if the cooking methods have been inadequate to kill possible enteropathogens, or it can become contaminated during storage. Cooked food should be protected from flies and other sources of recontamination.

The prevention and control of food and water-borne diseases will be influenced by the provision of training for various categories of health workers in the prevention and control of food and water-borne diseases.

Global Forum

The first ever Global Forum of Food Safety Regulators was held by WHO and FAO in Marrakech, Morocco, January 28-31, 2002. The documents are available at the site:- http://www.foodsafetyforum.org/global/

Information on the Web

Following is a list of pages on the WHO web site on different items related to the theme.

Antimicrobial-resistant bacterial infections

Assessment of food technology


Chemical contaminants in food


Diarrhoeal diseases / dysentery

Drinking water quality

Escherichia coli O157:H7

Food safety

Food-borne infections


Infant feeding

Intestinal nematodes



Sustainable water supply & sanitation

Typhoid Fever

Water & sanitation