Unit 7.3: Introduction to Epidemiology
Outline
Learning Objectives
After reading the following, you should be able to:
- Define epidemiology.
- Describe the different types of epidemiological studies.
- Describe healthcare-associated (nosocomial) infections.
- Explain why infections are more likely in a health-care setting, and name and describe the 3 factors that must interact to produce a nosocomial infection.
- Name three common pathogens involved in healthcare-associated infections
- Describe the top three sites of healthcare-associated infections from most to least common.
- Describe what is meant by “universal precautions” and relate these to the three factors that must interact to produce a healthcare-associated infection.
Epidemiology: The field of epidemiology concerns the geographical distribution and timing of infectious disease occurrences and how they are transmitted and maintained in nature, with the goal of recognizing and controlling outbreaks. The science of epidemiology includes etiology (the study of the causes of disease) and investigation of disease transmission (mechanisms by which a disease is spread).
Types of Epidemiological Studies: Today, epidemiologists make use of study designs, the manner in which data are gathered to test a hypothesis, similar to those of researchers studying other phenomena that occur in populations. These approaches can be divided into observational studies (in which subjects are not manipulated) and experimental studies (in which subjects are manipulated). Collectively, these studies give modern-day epidemiologists multiple tools for exploring the connections between infectious diseases and the populations of susceptible individuals they might infect.
- Observational Studies: In an observational study, data are gathered from study participants through measurements (such as physiological variables like white blood cell count), or answers to questions in interviews (such as recent travel or exercise frequency). The subjects in an observational study are typically chosen at random from a population of affected or unaffected individuals. However, the subjects in an observational study are in no way manipulated by the researcher. Observational studies are typically easier to carry out than experimental studies, and in certain situations they may be the only studies possible for ethical reasons.
Observational studies are only able to measure associations between disease occurrence and possible causative agents; they do not necessarily prove a causal relationship. For example, suppose a study finds an association between heavy coffee drinking and lower incidence of skin cancer. This might suggest that coffee prevents skin cancer, but there may be another unmeasured factor involved, such as the amount of sun exposure the participants receive. If it turns out that coffee drinkers work more in offices and spend less time outside in the sun than those who drink less coffee, then it may be possible that the