SYMPTOMS and SIGNS
Symptoms of food-borne illness generally include diarrhea and vomiting, and fever may or may not be present. Onset of disease varies greatly with the particular cause of disease. Symptoms can be due either to toxins that are present following the growth of pathogens in the food or to an actual infection that occurs in the intestinal tract after eating food contaminated with live pathogens. Symptoms from pre-formed toxins generally have fairly rapid onset (less than 24 hours) and are more likely to include vomiting. Food-borne infections generally require at least a day or two before symptoms appear, and in some cases may not be apparent for weeks. In general, disease caused by protozoan parasites shows slower progression compared to those caused by bacteria or viruses. Bloody diarrhea is generally a symptom of more serious food-borne pathogens, such as Escherichia coli or Shigella. Profuse watery diarrhea, such as that presented by cholera, can be rapidly life-threatening due to dehydration and also requires immediate attention. In susceptible persons, with serious underlying conditions that decrease their resistance to infection (HIV, hemochromatosis, liver disease, diabetes) food-borne infections may be more invasive, leaving the intestinal tract to become systemic and produce toxic shock and rapid death. Some of the more serious diseases, such as typhoid fever and cholera, threaten healthy persons and can cause very large epidemics.
Most persons with food-borne illness will recover without treatment. However, prolonged symptoms may lead to dehydration, which can have serious complications, especially in young children. Re-hydrating solutions are available to ensure both the return of both water and essential salts. Vaccines are available for some food-borne pathogens (V. cholerae, Salmonella, Hepatitis virus) but are generally administered to persons at high risk of exposure, such as travelers to countries where these diseases are endemic.
CAUSES and RELEVANCE to FLORIDA
Causes of food- or water- borne diseases include bacteria, viruses, and protozoan parasites. Non-infectious agents called prions transmit Mad Cow disease, but there is no evidence of this problem in US food supply. Viruses are probably the most common cause of food-borne illnesses and are also the one for which we have the least amount of information and protection. Viral infections generally produce self-limiting disease but can be rapidly spreading and extremely infectious. Florida cruise ships have had well-publicized outbreaks of norovirus (also call Norwalk virus) that has ruined many vacations. Food-borne illnesses are usually transmitted through ingestion of contaminated food or water, but even causal contact with contaminated surfaces may spread this virus. Salmonella and Campylobacter species are probably the most common source of bacterial infections. Parasitic infections are relatively rare in the US, but present a life-threatening concern to persons with compromised immune systems (HIV or the elderly).
The warmer weather in Florida permits more “tropical” pathogens, particularly parasites, to flourish. Also, foods exposed to warmer temperatures or temperature-abuse have increased growth rate of many microorganisms. Most pathogens grow best at body temperature (98.6F) so particular caution is needed when the air temperatures are over 90F. Warmer water temperatures can promote the growth in fish or shellfish of pathogens that may not be present in seafood harvested from cooler waters.
PREVENTION: WASH YOUR HANDS!
Most food- or water-borne pathogens are transmitted by fecal contaminants associated with poor personal hygiene. Particularly in Florida where so many people eat at places away from home and consume food that was handled by numerous preparers and servers, ample opportunity for contamination with feces can occur either before or after cooking. Therefore, hand washing is critical to maintaining safety in the food preparation and restaurant industries. Adequate hand washing for several minutes (sing “Happy Birthday” twice while washing) is required to kill most microbes. Even at home, improper hand washing can spread infection rapidly through the family. Contamination of surfaces with raw food is a common source of disease, and cutting boards and utensils should be cleaned thoroughly.
Food must be maintained at the appropriate temperatures and refrigerated at 4C or below. Thawing of frozen food should be done in the refrigerator, and thawed food should never be re-frozen. After cooking, maintain heat or transfer the food as soon as possible to the refrigerator. Check the sell-by dates on food packages and do not eat any products that show changes in appearance, smell, taste or texture. These changes generally indicate very high levels of bacteria (over 10,000,000) and may be dangerous to eat.
The food industry maintains a safe food environment through the HACCP program that ensures stringent protocols and critical review at each step in the food processing chain. However, awareness of food safety in the home is also essential to maintain safe food. Information about proper storage and treatment of raw and cooked products is available in stores and through many online services, including the Cooperative Extension Service.
Prepared by Anita C. Wright, Ph.D.
Associate Professor of Food Microbiology
University of Florida Food Science and Human Nutrition Department