Week 13

• Transmission in epidemiology refers to the process by which an organism must be transmitted, either directly or indirectly, from one place to another.
• Experimental Epidemiology is the study that describes the factors relevant to an outbreak of disease.
• Data are collected, collated according to time, place and person, and analyzed and inferences are drawn in Epidemic Investigation.
• Direct Transmission occurs when a reservoir and the susceptible host are in close proximity, closer than 6 feet.
• Direct Transmission can also occur from skin-to-skin contact, as with sexually transmitted disease or direct contact with a free-living organism in the environment.
• Droplet Spread occurs when infectious aerosols produced by coughing, talking, and sneezing transmit infection to a susceptible host.
• These infectious aerosols are large particles that are pulled to the ground by gravity and can only infect a new host within a distance of 6 feet.
• Indirect Transmission occurs when the reservoir and the susceptible host are separated.
• This separation can be as small as 6 feet or as large as thousand miles.
• Indirect Transmission can involve the transmission of an infectious agent from an animate organism, such as mosquitoes, fleas, mites, and ticks.
• Infectious agents may be transmitted through purely mechanical means, such as on the feet or the wings of the insect, or it may actually grow and multiply in the vector.
• Vehicle spread involves the transportation of an infectious agent or inanimate objects such as toys, school supplies, bedding, or biologic equipment, or in contaminated food, water, milk or biological supplies.
• Airborne spread involves droplet nuclei 1-5 microns in size, which are produced by talking, sneezing, coughing or singing and float on air currents over large distances for varying periods of time.
• The three major epidemiologic techniques are descriptive, analytic and experimental.
• Descriptive Epidemiology involves the collection of data that describe the occurrence of disease from various sources and the collation of these data by time, place and person.
• Descriptive Epidemiology:A lowering of the overall immunity of a population or a segment thereof can result in an increase in the occurrence of the disease.
• Analytic Epidemiology: Analyzes disease determinants for possible causal relationships, the two main analytic methods are the case-control (case-comparison) and the cohort method.
• Cohort Method: prospectively studies two populations: one that has had contact with the suspected causal factor under study and a similar group that has had no contact with the factor, advantages include accuracy of the collected data and the ability to make a direct estimate of the disease risk resulting from factor contact, more expensive.
• Cross-sectional study: a population is surveyed over a limited period to determine the relationship between a disease and variables present at the same time that may influence its occurrence.
• Case Control Method: starts with the effect and retrospectively investigates the cause of disease, relatively easy to conduct and can be completed in a shorter period, inexpensive and reproducible.
• Descriptive Epidemiology: Change in antigenic properties of the causative agent can lead to an increase in the occurrence of the disease.
• Descriptive Epidemiology:Epidemic occurrence is a sudden increase in occurrence due to prevalent factors that support transmission.
• Experimental Epidemiology: a hypothesis is developed and an experimental model is constructed in which one or more factors may be manipulated, manipulation will either confirm or disprove the hypothesis.
• Descriptive Epidemiology:Three different sites are considered in the description of epidemiologic data by place: Where the individual was when the disease occurred, Where the individual was when he or she became infected from the source, and Where the source became infected with the etiologic agent.
• Descriptive Epidemiology:Seasonal trend reflects the seasonal changes in disease occurrence following changes in environmental conditions that enhance the ability of the agent to replicate or be transmitted.
• Descriptive Epidemiology:The third focus of descriptive epidemiology is the infected person, all pertinent characteristics should be noted: age, sex, occupation, personal habits, socioeconomic status, immunization history, presence of underlying disease, and other data.
• Four trends are considered in describing the epidemiologic data: Secular trend describes the occurrence of disease over a prolonged period and is influenced by the degree of immunity of the population.
• Periodic trend is a temporary modification in the overall secular trend.