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level: Level 3

Questions and Answers List

level questions: Level 3

Question	Answer
determine the exposure status for each individual (clinical trial) or community (community trial); we then follow the individuals or communities to detect the effects of the exposure	Experimental
observe the exposure and outcome status of each study participant	Observational
Types of Observational study	1 cohort study 2 case-control study
categorize subjects on the basis of their exposure and then observe them to see if they develop the health conditions being studied It look at cause and proceed to effect study before the disease is manifest and proceed to study over a period of time for the disease to occur. Cohort means a group of people sharing a common experience.	cohort study
enroll a group of people with disease (“cases”) and a group without disease (“controls”) and compare their patterns of previous exposures It start from effect and then proceed to cause Both exposure and outcome have occurred before start of the study The study proceeds backwards from effect to cause Select subjects based on their disease status. The control group should ideally come from the same population that gave rise to the cases. Case control studies are usually faster and more cost effective	case-control study
simplest form of observational study. It is based on single examination of cross-section of population at one point of time. If the sampling methodology is accurate, results can be projected to the entire population. They are more useful for chronic illnesses, e.g. hypertension. save on time and resources, but provide very little information about natural history of disease and incidence of illness.	Cross-sectional studies is also called PREVALENCE STUDY.
Cause of disease is a factor (characteristic, behavior, event, etc.) that influences the occurrence of disease An increase in the factors leads to an increase in disease. Reduction of the factors leads to a reduction in disease	Causation
traditional model of infectious disease causation.	Epidemiologic triangle Agent -> Host -> Environment (Triangle)
1 susceptible human or animal who harbors and nourishes a disease-causing agent 2 a factor that causes or contributes to a health problem or condition 3 all the external factors surrounding the host that might influence vulnerability or resistance	1 Host 2 Agent 3 Environment
Infectious microorganism - must be present for disease to occur Virus Bacterium Parasite other microbe	Agent
1 Intrinsic factors that influence an individual’s exposure, susceptibility, or response to a causative agent. Age Race Sex socioeconomic status behaviors 2 Extrinsic factors which affect the agent and the opportunity for exposure physical factors biologic factors socioeconomic factors	1 Host factors 2 Environmental factors
Chain of Infection	1 Portal of entry - means by which an agent enters a susceptible host 2 Host - individual infected with the agent 3 Reservoir of an agent - is the habitat in which an infectious agent normally lives, grows, and multiplies 4 Portal of exit - is the path by which an agent leaves the source host
(Chain of Infection) Modes of transmission	1 Direct - Direct contact - Droplet spread 2 Indirect - Airborne - Vehicle borne - Vector borne - Mechanical - Biologic
1 immediate transfer of the agent from a reservoir to a susceptible host by direct contact or droplet spread Direct contact Droplet spread 2 an agent is carried from a reservoir to a susceptible host by suspended air particles or by animate (vector) or inanimate (vehicle) intermediaries Airborne Vehicle borne Vector borne Mechanical Biologic	1 Direct 2 Indirect
Relationship between a cause and its effect	1) Chain of Causation 2) Multiple Causation