Epidemiology pt. 2 Flashcards
Epidemiology
the study of the distribution of states of health and of the determinants of deviations from health in human populations
Epidemiologists
investigate both infectious and noninfectious diseases - chronic conditions such as cardiovascular disease, cancer, and diabetes; acute events or illnesses; and mental and emotional disorders
John Snow
First epidemiological investigations
- cholera outbreak
When determining the distribution of any disease or injury epidemiologists examine:
incidence, prevalence, and mortality rates
Incidence Rate
the rate at which disease occurs in a population at risk over one year
Mortality or Death Rates
refer to the number of deaths for either all causes or for a specific disease, condition, or age group. Other frequently calculated mortality rates including age specific death rate, cause-specific death rate, maternal mortality rate, and neonatal and infant mortality rates, provide information about the health of a population, as well as the country in general.
natural history of disease
helps to identify approaches to prevention, treatment, and control. the progress of a disease is influenced by the epidemiological triangle, which consists of the disease-producing agent, the affected host, and the environment.
The pre-pathogenesis
before the disease actually occurs. the interaction of these three components may alter the host’s susceptibility.
Pathogenesis period
pathological changes leading to disease take place in the host
Goals of an Outbreak Investigation
- identify the etiologic agent
- identify the reservoir
- identify the mode of transmission
- eliminate the reservoir and transmission
- prevent further outbreaks
Role of CHNs in outbreak investigation
CHNs operate throughout the process… similar to the infection control nurse in Acute Care, there are CHNs who are specialists in the community. All CHNs, however, are mandated as public health nurses to respond to outbreaks as a priority concern.
When outbreak or epidemic is suspected…
there are a series of actions that are taken. The first step is to confirm that an outbreak exists by case-finding and comparing current numbers of an illness to the baseline. Verification of the diagnosis of cases at this point is essential to initiate appropriate control measures.
It is also important to search for…
additional cases that may have been unrecognized or unreported. The cases should be characterized by person, place, and time.
Epidemiologic curve
a curve in which the cases are plotted using a histogram that covers the period of the outbreak, the exposure, and the date of onset. Useful in determining incubation periods by charting the time of exposure to the time of illness onset.
- graphic display of outbreak with time (hours, minutes, days, weeks, months, years) on the x-axis and the number of persons meeting the case definition on the y-axis
- both pre-epidemic and epidemic periods should be plotted.
Outbreak Investigation Summary
- Surveillance (ongoing role of nurses and other public health professionals prior to outbreak)
- Case definition (when outbreak is suspected - clinical description to guide field workers for case finding)
- Case finding (field work)
- ‘line list’ (listing data in a table to quickly identify risk factors and outbreak staring point and movement - timeline (sourcepoint) line of infection (risk factors)
- Identify common exposures
- introduce control measures
Infectivity
the ability of an organism to cause infection in a susceptible house
Pathogenicity
the capacity of an organism to cause disease to a host
Virulence
the severity of illness or disease that an organism causes in its host
Attack Rate
a type of incidence rate calculated for a particular group in a specific event or outbreak, expressed as a percentage
- can be expressed in numbers of people affected, numbers of adverse outcomes, or numbers of infections/diagnoses:
- number of people affected divided by number of people at risk
- number of infections divided by number of people at risk
- number of adverse outcomes divided by number of people at risk
Attack Rate formula
the cumulative incidence of infection in a group observed during an epidemic / number of people exposed x 100
Factors contributing to pathogenicity
- its ability to survive in the environment between hosts, attach to receptor surfaces, proliferate locally, create local tissue damage, invade and disseminate, and alter the cell wall or membrane.
- organisms that have an effective mode of transmission between hosts can also be more effective in producing illness.
Formula for Relative Rate of Risk
attack rate for people who were exposed to the agent/attack rate for those who were not exposed
Gathering Data
preventative efforts are only as effective as the information on which they are based.
Analysis of current epidemiological situations are future predictions are dependent on accurate data gathered through descriptive, analytical, and experimental studies
Descriptive Studies
Descriptive studies are observations of when and where diseases or injuries occur and who they affect (person, place, and time)
- they describe the onset and duration of events and seasonal trends in relationship to physical, economic, and family environments.
- include age, gender, ethnicity, socioeconomic status, and overall health status of the affected individuals, as well as personality traits, environmental exposures, and personal lifestyle factors, such as smoking, drinking, and health history.
Analytical studies
analytical studies use data from descriptive research to formulate and answer specific questions about variations in incidence and prevalence of diseases and injuries in different populations. The primary purpose is to examine associations and test hypotheses.
Differences in purpose, time frame, strengths, and limitations determine if these studies are cross sectional, case-control, or cohort
Cross-Sectional or Prevalence Studies
Cross-sectional, or prevalence studies, examine relationships between disease and other characteristics of a specific population at one point in time. Although a cross-sectional study may demonstrate the simultaneous occurrence of a health factor and a particular health outcome during the same time period, it doesn’t necessarily establish a cause and effect relationship.
Case-Control or retrospective studies
investigate disease by using two groups - cases (people who have the condition) and controls (those who do not) - selected from institutional or community setting. a good design for examining chronic illnesses, rare diseases, and long-term effects related to exposure.
Cohort, prospective, longitudinal studies
involve the use of groups of people who are presumed to be free of disease or condition but differ in the extent of exposure to the studied factor. Subjects are followed over a period of time to evaluate the development of disease.
Translating Epidemiological Findings Into Best Practice
- The volumes of descriptive data gathered during epidemiological studies provide a solid foundation on which to build and implement best practices. This can be a long process that evolves over time.
- As the evidence base becomes more fine-tuned, healthcare practitioners are able to identify appropriate interventions that are most likely to produce optimal outcomes.
- The public is also becoming more informed about best practices, and expectations are high that these practices will be followed.
Experimental Studies
Experimental studies are designed as a result of previous research that indicates a specific factor that may be related to a specific outcome, such as an illness or injury. An experimental study requires the manipulation or control of conditions under which the investigation is conducted.
- Randomization helps to reduce selection bias and ensure that when confounding occurs, it is equally distributed between the groups
