Agent factors Of course, these factors are only applicable in the case of diseases with causative or associated agents which may include prions, viruses, bacteria, protozoa and transmissible cancers. Features of the agent which affect the levels of disease within an infected population include infectivity the ability of the agent to establish infectionpathogenicity the ability of the agent to produce disease and virulence the severity of the resultant diseasealong with characteristics of the life cycle of the pathogen such as incubation period the time between infection and diseaselatent period the time between infection and infectiousness and the infectious period the duration over which the pathogen can be transmitted to others. It is important to note that many of these characteristics are as much characteristics of the host as of the agent, and indeed this relationship is often dynamic - with host characteristics impacting upon agent characteristics and vice versa. Environment factors This category includes a wide variety of factors which are neither directly associated with host or agent characteristics, and encompasses animal husbandry, climatic and geographical features, amongst others.
Analytic Epidemiology As noted earlier, descriptive epidemiology can identify patterns among cases and in populations by time, place and person. From these observations, epidemiologists develop hypotheses about the causes of these patterns and about the factors that increase risk of disease.
In other words, epidemiologists can use descriptive epidemiology to generate hypotheses, but only rarely to test those hypotheses. For that, epidemiologists must turn to analytic epidemiology.
Consider a large outbreak of hepatitis A that occurred in Pennsylvania in While the investigators were able to narrow down their hypotheses to the restaurant and were able to exclude the food preparers and servers as the source, they did not know which particular food may have been contaminated.
The investigators asked the case-patients which restaurant foods they had eaten, but that only indicated which foods were popular.
The investigators, therefore, also enrolled and interviewed a comparison or control group — a group of persons who had eaten at the restaurant during the same period but who did not get sick. Further investigation of the ingredients in the salsa implicated green onions as the source of infection.
Shortly thereafter, the Food and Drug Administration issued an advisory to the public about green onions and risk of hepatitis A. This action was in direct response to the convincing results of the analytic epidemiology, which compared the exposure history of case-patients with that of an appropriate comparison group.
When investigators find that persons with a particular characteristic are more likely than those without the characteristic to contract a disease, the characteristic is said to be associated with the disease.
The characteristic may be a: Demographic factor such as age, race, or sex; Constitutional factor such as blood group or immune status; Behavior or act such as smoking or having eaten salsa; or Circumstance such as living near a toxic waste site.
Identifying factors associated with disease help health officials appropriately target public health prevention and control activities.
It also guides additional research into the causes of disease. Thus, analytic epidemiology is concerned with the search for causes and effects, or the why and the how.
Epidemiologists use analytic epidemiology to quantify the association between exposures and outcomes and to test hypotheses about causal relationships. It has been said that epidemiology by itself can never prove that a particular exposure caused a particular outcome.
Often, however, epidemiology provides sufficient evidence to take appropriate control and prevention measures. Epidemiologic studies fall into two categories: Experimental studies In an experimental study, the investigator determines through a controlled process the exposure for each individual clinical trial or community community trialand then tracks the individuals or communities over time to detect the effects of the exposure.
For example, in a clinical trial of a new vaccine, the investigator may randomly assign some of the participants to receive the new vaccine, while others receive a placebo shot. The investigator then tracks all participants, observes who gets the disease that the new vaccine is intended to prevent, and compares the two groups new vaccine vs.
Similarly, in a trial to prevent onset of diabetes among high-risk individuals, investigators randomly assigned enrollees to one of three groups — placebo, an anti-diabetes drug, or lifestyle intervention. At the end of the follow-up period, investigators found the lowest incidence of diabetes in the lifestyle intervention group, the next lowest in the anti-diabetic drug group, and the highest in the placebo group.
The two most common types of observational studies are cohort studies and case-control studies; a third type is cross-sectional studies. A cohort study is similar in concept to the experimental study.
Case-control and cohort studies are observational studies that lie near the middle of the hierarchy of evidence. These types of studies, along with randomised controlled trials, constitute analytical studies, whereas case reports and case series define descriptive studies (1). CASE CONTROL STUDY Facilitator: Dr. NAVPREET. Assistant Professor, Department of Community Medicine. Govt. Medical College & Hospital, Chandigarh. Specific Learning Objectives ANALYTICAL EPIDEMIOLOGY • Testing a hypothesis – Statistical. and case-control studies – in greater depth. The study designs discussed in this chapter are called analytic because they are generally (not always) employed to test one or more specific hypotheses, typically whether an exposure is a risk factor for a.
In a cohort study the epidemiologist records whether each study participant is exposed or not, and then tracks the participants to see if they develop the disease of interest.
After a period of time, the investigator compares the disease rate in the exposed group with the disease rate in the unexposed group. The unexposed group serves as the comparison group, providing an estimate of the baseline or expected amount of disease occurrence in the community.
If the disease rate is substantively different in the exposed group compared to the unexposed group, the exposure is said to be associated with illness. The length of follow-up varies considerably.Case-control and cohort studies are observational studies that lie near the middle of the hierarchy of evidence.
These types of studies, along with randomised controlled trials, constitute analytical studies, whereas case reports and case series define descriptive studies (1). A case-control study is a retrospective study that looks back in time to find the relative risk between a specific exposure (e.g.
second hand tobacco smoke) and an outcome (e.g. cancer).
A control group of people who do not have the disease or who did not experience the event is used for comparison. They differ from case-control studies in that they aim to provide data on the entire population under study, whereas case-control studies typically include only individuals with a specific characteristic, with a sample, often a tiny minority, of the rest of the population.
epidemiology EVERYTHING. STUDY. PLAY. Matching in a case-control study is a strategy used to control for confounding. This approach involves what level of the study? both design and analysis. Which of the following is typically not a type of analytic epidemiology study? Case-control study – is one of the three basic analytical observational study designs.
A case-control study starts by defining groups according to the outcome (e.g. disease present or absent) and then looks back to establish the study factor (e.g. exposure present or absent). and case-control studies – in greater depth. The study designs discussed in this chapter are called analytic because they are generally (not always) employed to test one or more specific hypotheses, typically whether an exposure is a risk factor for a.