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A course for staff of the Global Center for Mass Medicine at the Ministry of Health by Dr Omar Hasan Kasule MB ChB (MUK), MPH (Harvard), DrPH (Harvard) Professor of Epidemiology at King Fahad Medical City Riyadh
4.1 ENVIRONMENTAL EXPOSURES:
4.1.1 Environmental epidemiology studies the causes and prevention of environmental disease. The objective is to eliminate a hazard or set a safe exposure limit
4.1.2 Commonest causes of air pollution are automobile emissions, fossil fuel energy plants, and industrial plants. Water pollution is due to municipal sewage or industrial pollutants. Soil pollution is by solid waste (residential, commercial, mining, industrial, municipal, and agricultural), hazardous waste (industrial and medical), or sewage.
4.1.3 Epidemiological studies may show an exposure-disease relation but with insufficient evidence. Laboratory level confirmation is needed.
4.1.4 Risk assessment is an analytic process of combining information on human exposure to environmental agents with data on health effects to produce the probability or frequency of health effects in a population
4.2 OCCUPATIONAL EXPOSURES:
4.2.1 Data on occupational diseases is limited and is unreliable. Job histories and exposures are difficult to document because they change often.
4.2.2 Occupational hazards can be psychological stress, physical hazards (electrical, noise, radiological, temperature, and vibration), chemical hazards, biological hazards, and ergonomical hazards.
4.2.3 Epidemiological studies investigate suspected hazards, determine quantitative relation between hazards and disease, and assess the effectiveness of the intervention.
4.2.4 Prevention of Occupational Disease: Primary prevention is to reduce exposure. Secondary prevention is reducing the effects of the exposure by control (engineering control, personal protection, standards, isolation, ventilation, and education). Tertiary prevention is reducing the effects of the disease (complications and disability).
4.3 NUTRITIONAL EXPOSURES:
4.3.1 Nutritional epidemiology studies the relationship between diet and disease.
4.3.2 PEM occurs in children in LDC and adults in hospital. Obesity is worldwide being more in DC and high SES. Micronutrient deficiencies are worldwide.
4.3.3 Diseases Associated with Malnutrition: hypertension (high sodium intake), CHD (high dietary unsaturated fats, low dietary fiber), colon cancer (high protein, high fat, low fiber), diabetes type 2 (high fat and low fiber).
4.3.4 Assessment of Nutritional Status: Dietary intake can also be measured as its effects either biochemical or anthropometric (weight and height).
4.3.5 Epidemiological Studies of Nutritional Exposures: Dietary habits, anthropometry, and biological assays can be used both as exposure or outcome variables depending on the hypotheses of the study. Morbidity and mortality are used as outcome measures. All nutritional studies share the problem of imprecise and nonspecific measurement of food intake.
4.4 RADIATION EXPOSURES:
4.4.1 Radiation is used medically in diagnostic procedures (x-rays, radioisotopes) and treatment of malignancies. It also has military and industrial uses. Exposure to radiation is a cause of disease.
4.4.2 There are 2 main sources of radiation in the environment: background natural radiation (cosmic or solar from space such as UV, geological /terrestrial from the rocks, inhaled radioactive material, and the radioactive gas radon) and man-made radioactive sources (nuclear bombs, emissions from nuclear power plants, medical exposure, residential exposures to TV and appliance, and occupational exposures).
4.4.3 Effects of Radiation: Ionizing radiations cause DNA damage, DNA mutations, and chromosomal aberrations. Health effects of radiation may be acute (sunburn, photosensitivity, and acute radiation syndrome) or chronic (cancer, infertility, teratogenesis, and dermatological). There is a disagreement about the existence of a threshold.
4.4.4 The objective of an epidemiological study is to relate exposure to health effects and to relate dose to biological effects
4.4.5 Primary prevention is to prevent or limit exposure Secondary prevention is mostly supportive: treatment of infection, replacement of bone marrow, etc), Tertiary prevention is by long-term follow-up for those exposed because effects may appear late. Genetic counseling may be necessary.
4.5 OTHER EXPOSURES:
4.5.1 Biological Markers: Molecular epidemiology is the use of biological markers (cellular, biochemical, molecular, genetic, immunologic, or physiological) to study disease-exposure relations. Both exposure and outcome biomarkers are used
4.5.2 Genetic Exposures: Genetic epidemiology investigates the role of genetic factors and their interaction with environmental factors in disease etiology. Primary prevention of genetic disease is by genetic counseling. Secondary prevention is by surgical correction, replacement therapy
4.5.3. Adverse Drug Reactions (ADR): Primary prevention of Adverse drug reactions (ADR) is by control of prescription, knowing allergies avoiding polypharmacy, and rational drug use. Secondary prevention of ADR is by stopping the drug, using an antidote, monitoring for further side effects. Post-marketing surveillance of drugs is necessary to pick up more ADRs.
4.5.4 Drug interactions: 10-20% of all ADR are due to drug interactions. Primary prevention is by recording all drugs the patient is taking and making sure no drugs known to interact are given. Secondary prevention is by stopping/substituting one of the pairs of interacting drugs. Tertiary prevention is by treating any complications.