Epidemiology The study of distribution and determinants of disease frequency in human population .
epidemiology is divided into : 1. Descriptive epidemiology . 2. Analytic epidemiology .
Descriptive epidemiology : Describes the distribution of disease in a population , and observing the basic feature of its distribution in terms of person , place and time , the typical study design for descriptive study is ( cross-sectional study) .
many types of descriptive studies: 1. on populations ( correlational studies) 2. on individuals : a. case reports . b. case series. c. cross sectional surveys.
Descriptive studies raise the question of association rather than proving it.
Analytic epidemiology : Testing a specific hypothesis about the relationship of a disease to putative cause , by conducting an epidemiologic study that relate the exposure of interest to the disease of inertest . typical study designs: cohort , case- control studies . also we have intervention studies or what called clinical trial or experimental studies.
The basic triad of descriptive Epidemiology the three essential characteristics of disease we look for in descriptive epidemiology are: 1. person . 2.place. 3.time.
Person Who is getting the diseases ? many variables are involved and studied , but factors like sex , age and race have a major effect .
Characteristics of person : . Age . Sex (gender) .Ethnic group .Socioeconomic status .Nativity .Religion .marital status .Occupation
Place .Where are the rates higher ? lower? . Geographic location of source .Geographic location of reservoir
5 criteria of place : 1. high rate observed in all ethnic group in the area . 2. high rate NOT observed in persons of similar groups inhabiting other areas . 3. Healthy persons entering area get ill at same frequency . 4. people who leave do NOT show similar levels . 5. Similar levels of infestation in other species ( if zoonotic disaes).
characteristics relating to place: . International .Variation within countries
Urban-rural Local .Building maps
Interaction of time and place : 1.Time-place clustering . 2. Migration .
Time .When does the disease occur ? "Temporal " Range from hours to decades
Characteristics relating to time : 1. Secular change (long-term) . 2.Point epidemics (short-term) . 3. Cyclic trends. 4.Seasonal variation.
.Descriptive epidemiology is a necessary antecedent of analytic epidemiology
To undertaken an analytic epidemiology study you must first : . know where to look .know what to control for .be able to formulate hypotheses compatible with laboratory evidence.
A common error in epidemiology is moving to analytic epidemiology without having a solid base in the descriptive epidemiology of the condition .
Population at risk It is a frequent term in the epidemiology that denotes to the sharing of a characteristic by certain population subgroup that put them at increased risk for development of a health outcome ( disease , death , ...)
so the population at risk is : any group that is susceptible and exposed to risk factor .( they should have both criteria to be population at risk) .
In previous definition , we have the word " characteristic " and there are 3 types of characteristics : 1. Biological : which includes the sex (gender) , age , genetic factors, ..... 2. Environmental : such as being nearby chemical factories or near polluted water resources. 3. Socioeconomical : such as nutritional status , poverty , ....
Risk : a term which denotes to the more probability for having an outcome . Risk factor : a condition , physical characteristics or behavior that increase the probability that a currently healthy individual will develop a particular disease . Outcome : it's the notement at the disease status , so it may be death or accident or handicaps.
Types of risk factors 1/ Environmental risk factors : they are found in the physical environment ( infectious organisms, pollutant , toxins , and drugs ) , 2/ Behavioral ( life habit) risk factors include such behavior as smoking and failing to observe occupational safety precaution .
Types of risk factors 3/ Social risk factors : like divorce , death of family member and job loss. 4/ Genetic risk factors : are inherited factors ex.( familial hypercholesterolemia ) which increase the risk of coronary artery disease .
Relationship of risk factors to disease A risk factor may be a causal factor of disease or merely a marker for increased probability of disease , for example: while poor prenatal care and drug use constitute causal factors for neonatal mortality , the socioeconomic status would be consider a marker for neonatal mortality .