Epidemiology is the science that studies when and where diseases occur and how they are transmitted.

Modern epidemiology again with the work of John Snow 150 years ago who investigated outbreaks of cholera in London. He analyzed the death records attributed to cholera, gathered information about the victims of the disease, and interviewed survivors of the disease. Using this information, he made a map that showed that most individuals who died of cholera drank water from a certain pump. After he removed this pump, the number of cholera cases dropped significantly. Snow’s method of analyzing a disease based on when and where it occurs was a new approach to medical research.

Today, epidemiologist use three basic types of investigations when analyzing the occurrence of a disease: descriptive, analytical, and experimental. The first two will be considered here.

Descriptive epidemiology entails collecting all data that describe the occurrence of the disease i.e. relevant information about the affected individuals and the place and period in which the disease occurred. These methods are usually retrospective in which one looks backwards after the disease has ended i.e. one backtracks to the cause and source of the disease.

Analytical epidemiology entails the investigations and comparison of people who have been exposed to a hazard and have become ill to those who have not. These studies can be done in different ways. In the case control method, a group of people who have the disease are compared with another group of people who do not have the disease. The people who have the disease are examined to determine what exposures they are receiving now or could have received in the past that could the source of disease. These studies are retrospective. Examples of case control studies in environmental health include the association of cigarettes and lung cancer.

In cohort studies, individuals who have received unusual exposures are followed over time to determine what diseases they develop and whether there is an increase in the incidence of those disease that might be presumed to have been caused by the exposure. Epidemiologic studies of survivors of World War II exemplify these studies.

HOW A TYPICAL OUTBREAK OF FOODBORNE DISEASE MIGHT BE EPIDEMIOLOGICALLY INVESTIGATED

1. Physician sees more than one individual with symptoms resembling foodborne disease or an individual with symptoms suggestive of one of the more virulent food borne pathogens e.g. E. coli O157:H7.

2. Physician calls other physicians and/or local health department to see if other cases have appeared.

3. Depending on the extent of the disease, the State Health Department or Centers for Disease Control and Prevention may become involved.

4. Epidemiologist from these agencies collect the isolated organisms from these individuals and compare them by a variety of identification procedures with the most definitive being molecular techniques whereby the number and sizes of the DNA pieces of the organisms are compared. See handout on PulseNet which is a new national molecular subtyping network for investigating foodborne disease. Epidemiologist also use case control methods whereby they interview people with and without the disease and try to determine a common source exposure.

TWO FEDERAL AGENCIES PRIMARILY RESPONSIBLE FOR REGULATING SAFETY OF FOODS

1. "FDA - Food and Drug Administration at present, the FDA is a part of the Federal Public Health Services in the Department of Health and Human Services. It is delegated the power to administer the federal Food, Drug and Cosmetic (FD&C) Act. In that capacity, the FDA ensures the safety and wholesomeness of all foods, except meat, poultry, and eggs sold in interstate commerce, as well as exported and imported foods. The safety and wholesomeness of foods served on planes, trains, and buses are also inspected by the FDA. It also conducts research to improve detection and prevention of contamination of food, develops regulatory testing procedures, specifications, and standards, and enforces regulations on processing and sanitation of foods and processing facilities. The FDA sets up specific microbiological criteria that contain specifications (toleration levels) for aerobic plate counts (APC), coli forms, Esc. Coli, coagulase-positive Sta. Aureus, pathogens, and mycotoxins in various foods. FDA inspectors inspect processing plants once every 2 to 3 years, unless a processor is in violation and a food has hazard potential. The FDA also helps processors develop their effective sanitation programs as well as gives contracts to state regulatory agencies to inspect plants. For foreign countries interested in exporting food to the United States, the FDA sends inspectors to help improve their food quality according to U.S. regulations.

In case of violations, the agency sends formal notice of violation to the offender and sets a date (usually 10 d) by which the problem needs to be corrected. In case of failure, depending upon the severity of the offense, the FDA is authorized to take legal action, through the Department of Justice, that includes seizure of products, destruction of products, and criminal prosecution of the offenders. This includes products produced in the United States as well as imported products. In addition to microbiological quality and safety of foods, the FDA is also responsible for testing foods for composition, nutritional quality, food additives, food labeling, and pesticide residues (some with other agencies). FDA also conducts market basket survey to test certain number of foods (imported and produced in the United States) for safety and other qualities." From p. 483, Ray, Fundamental Food Microbiology.

2. "Under the Wholesome Meat Act and the Wholesome Poultry Product Act, the FSIS is responsible for inspection of slaughtering facilities of food animals and birds, and the production of wholesome and safe meat, poultry, eggs, and egg products that are sold in interstate commerce or imported. The FSIS also sets up microbiological specifications, particularly pathogen levels, for some of these products. It also conducts research on food safety and quality." From p. 483, Ray, Fundamental Food Microbiology.

INFORMATION REGULATORY AGENCIES USE IN MAKING REGULATIONS CONCERNING FOOD

RISK ASSESSMENT - Assessing the risk of the food to impairment of human health. This assessment is based on the likelihood of occurrence of problems in food (microbiological, chemical and physical hazards with microbiological By and for the largest) and the severity of the problem. It should be noted that the Of risk assessment used as a decision making tool in governmental agencies is relatively new and although it is agreed that this is a rational and logical approach, this assessment is only as good as the scientific evidence that is available and in many cases we have very little scientific data.

ECONOMIC IMPLICATIONS OF CONTROL MEASURES

CONSUMER/POLITICAL IMPLICATIONS OF CONTROL MEASURES

In summary, regulatory decisions involve an analysis of the scientific, economic, and political issues. An example is the recent regulation of FDA to require the labeling of all unpasteurized juice and the proposed standard that most juice manufacturers develop a HAACP (Hazard Analysis and Critical Control Points) program. This program was originally developed by USDA to insure the safety of seafood and later the safety of meat and poultry.

SKIN

Normal flora produces free fattyacids which inhibit growth of other microorganisms.

Skin infections occur when continuity of skin is broken.

RESPIRATORY TRACT

Particles entrapped in nasal cavity are swept by beating action of cilia along mucous stream to the back of the throat where they are swallowed and destroyed by low pH of stomach.

Coughing and sneezing

GASTROINTESTINAL TRACT

Production of hydrochloric acid
Peristalsis of small intestine, normal flora, secratory IgA, enzymes, etc.

UROGENITAL TRACT

Normal flushing action and pH of urine
Production of lactic acid by normal flora of the vagina

CONJUNCTIVA

Flushing action of tears
Lysozyme

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