Basic Epidemiology Notes

Two types of Data according to Source: ƒ Primary Data - obtained by the investigator o Example: interviews, physical examination, laboratory exams o More accurate and up-to-date ƒ Secondary Data - data actually gathered by other individuals or agencies o Example: published reports, clinical/hospital records, census o more readily available but incomplete o confidentiality of information

Surveillance ƒ In most health departments, routinely collected statistics provide the key data for monitoring morbidity and mortality trends. ƒ Surveillance System – includes a functional capacity for data collection, analysis and dissemination linked to public health programs.

Epidemiologic Surveillance ƒ Has been defined by the Centers for Disease Control (CDC) as the ongoing systematic collection, analysis and interpretation of health data essential to the planning, implementation and evaluation of public health practice, closely integrated with the timely dissemination of these data to those who need to know.

Other Sources of Surveillance Data ƒ Hospital and medical care statistics ƒ Panels of cooperating physicians ƒ Public health laboratory reports ƒ Absenteeism from work or school ƒ Telephone and household surveys ƒ Newspaper and news broadcasting reports Locally, data may be available from: ƒ Department of Health ƒ National Institutes of Health ƒ Medical Specialty Societies ƒ National Congenital Defects Registry ƒ Newborn Screening Program ƒ Specialty Hospitals ƒ National Census and Statistics Office Descriptive Epidemiology: Person, Place and Time ƒ The study of the amount and distribution of disease within a population by person, place and time. ƒ WHO (person) is affected? ƒ WHERE (place) do the cases occur? ƒ WHEN (time) does it happen? Person ƒ

Age ƒ

Specific Data that are Useful in Epidemiologic Studies ƒ Data on vital events o Birth, death, marriages, divorces, adoptions, total births/deaths, deaths by specific causes, mortality rate, case fatality rate, etc. ƒ Diseases statistics o prevalence and incidence of specific diseases ƒ Data on physiologic or pathologic conditions o Prenatal Hgb levels, blood sugar levels among diabetics, BP readings ƒ Statistics on Health Resources and Services o Number of hospital beds, vaccine vials consumed, number of health center staff ƒ Statistics pertaining to the environment o Number of households with sanitary water source, number of snail breeding places, amount of pollution in the air, level of noise in the factory, workers’ protective gears ƒ Demographic data o Total number of population, age groups, gender, rural-urban residence, occupation, income ƒ Socio-cultural data o Knowledge, attitude, practices of people regarding health

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The most important determinant among the personal variables Death rate is fairly high in infancy Lowest point is between 5-14 years old Doubling in rate from 40 and every decade of life Chronic conditions tend to increase with age whereas the relation of age to acute infectious diseases is less consistent Age is related to the frequency and severity of infectious diseases High rate of injury in particular age group

Sex ƒ ƒ ƒ ƒ ƒ ƒ ƒ ƒ

10 Key Sources of Data for Surveillance Systems Designed by the WHO ƒ Mortality registration ƒ Morbidity reporting ƒ Epidemic reporting ƒ Laboratory investigation ƒ Individual case investigations ƒ Epidemic field investigations ƒ Surveys ƒ Animal-reservoir and vector distribution studies ƒ Biologic and drug utilizations ƒ Knowledge of the population and the environment

Age, sex, ethnic group, social class, occupation exposures, marital status, family variables, etc.

Death rates are higher for males than females, but morbidity rates are higher for females In utero and neonatal death rates are also higher for males The higher death rates for males throughout life may be due to sex-linked inheritance, differences in hormonal balance, environment or habit patterns The higher mortality rate for men are not paralleled by higher rates of illness Women have more episodes of illness and more physician contacts than men have Rate of attempted suicide is higher in women but completed suicides are more common in men Toxic shock syndrome o Irritant tampons Possible explanations for relatively high morbidity and low mortality in women: o Women seek medical care more freely and perhaps at an earlier age of disease

Ethnic Group and Race ƒ Blacks have higher rates of death caused by CHVD, VCA, TB, SY ƒ Whites have higher rates of death from suicide, leukemia and atherosclerosis Social Class ƒ Difference in wealth, power, prestige: difference in access to medical care and facilities ƒ Poverty affects utilization of medical services ƒ More common cases of mental illness in lower strata

©2007 Mikey

Occupation ƒ This influence may occur through a variety of exposures o Unfavorable physical conditions ƒ Heat, cold changes in atmosphere o Chemicals o Noise o Stress in work ƒ Silica (pulmonary fibrosis) ƒ Asbestos (lung cancer) ƒ Aniline dyes (bladder cancer) ƒ Injury, trauma, social and psychological climate of the job or workplace

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Prevalence = no. of existing cases of a disease / total population Incidence – refers to the proportion of the population who developed the disease in a given interval time Cumulative incidence = no. of new cases of disease / population at risk The higher the number of new (incident) cases, then there would be a greater number of existing (prevalent) cases

Marital Status ƒ Marital status is associated with level of mortality for both sexes ƒ Psychological and physical support from the spouse ƒ For women, marital status may also be related to health through differences in sexual exposure, pregnancy, childbearing and lactation Family Variables ƒ Family size: larger families – especially if they are poor, children may be in a disadvantage: higher rates of fetal, neonatal and infant deaths, higher childhood mortality, and a tendency to poorer intellectual performance ƒ Birth Order: first borns tend to be more healthy and better educated. Personal Variables ƒ Maternal age: etiologic importance in congenital malformations ƒ Parental deprivation – psychiatric, psychosomatic disorders, TB incidence, attempted suicides and accident repeaters ƒ Blood type A – gastric CA, Type O – duodenal ulcer ƒ Environmental exposure ƒ Personality traits – medical advice, compliance Place ƒ ƒ ƒ ƒ ƒ

Frequency of disease can be related to place of occurrence in terms of areas set off either by natural barriers or by political boundaries Frequency of disease may be related to temperature, humidity, rainfall, altitude, mineral content of soil or water supply Lack of iodine, mottled dental enamel Rural-urban differences Migrants in national and international borders

Time ƒ ƒ ƒ

Disease occurrence is usually expressed on a monthly or annual basis Secular trends – refers to changes over a long period of time, years, decades Cyclic change – refers to recurrent alterations in the frequency of disease

Measures of Disease Frequency ƒ Count – the basic measure of disease frequency ƒ Ratio – a measure that shows the relationship between quantities ƒ Proportion – the numerator in the proportion is part of the denominator ƒ Rate – the most common measure Measures of Morbidity ƒ Prevalence – the proportion of individuals with the disease during a given point in time ƒ The probability that a person randomly chosen from the population will have a disease at the time he was examined

©2007 Mikey