EPIDEMIOLOGY

SAMAR MUSMAR

Basic epidemiologic concepts• Epidemiology comes from the Greek words

epi, meaning “on or upon,” demos,meaning “people,” and logos, meaning “the study

• Defin: the study of factors that determine the occurrence and distribution of dse in a population

• One of ways in which dse is studied—4 ways of scientific study of dse:

1. Sub molecular and molecular—cell biology immunology biochem

2. Tissue or organ level—anatomic pathology3. Individual pt level—clinical medicine4. Population level--epidemiology

Historical background

• Hippocrates--suggested that environmental and host factors such as behaviors might influence the development of disease

• John Graunt--in1662,was the first to quantify patterns of birth, death, and disease occurrence, noting male-female disparities, high infant mortality, urban-rural differences, and seasonal variations

• William Farr,1880 considered the father of modern vital statistics and surveillance, developed many of the basic practices used today in vital statistics and disease classification

• Snow—father of epidemiology—analysis of data for cholera outbreak—mid 19th century

• Real science –after wwII

Classical/clinical epidemiology

• Classical—pop-oriented studies community origins of health problems, nutrition, enviro, human behavior, psychological, social, spiritual.

• Interested in finding risk factors• Clinical—use similar research design and

statistical tools,but studies pts in healthcare settings in order to improve dx tx and prognosis of pts(already have dse)

• Sometimes called—clinical decision analysis

Infectious dse epid/ch dse epid

• Infectious—heavily depends on lab(micro &serology)

• Chronic—heavily depends on complex statistical methods

• Not absolute difference

• Some inf also considered ch (T.B. HIV )

Etiology and natural hx of dse

• Natural hx—progression of dse without medical or public health intervention

• Stages of dse—predse,latent,symptomatic• Predse—before pathologic process begins—

early intervention--? Prevention• Latent stage—dse has begun ,still asympt—

screening and institute tx--? Prevention• Symptomatic stage—dse manifestaion—evident

—intervention arrest ,slow,or reverse progression--?prevention

Mechanisms & causes of dses

• Biologic mech, social & environmental causes—contemplating—

• e.g diet lifestyle –dyslipidemia

• E.g osteomalacia—muslim community?

Triad:host,agent,environment• ? 4th—vector• Host: degree individual able to adapt to stressor

(resistance)• factors: genetic,nutritional,immune system,and social

behavior• Examples• Nutrition immunecompetent/ • Personal hygiene • Agents of dse: Biological,chemical,physical,social &

psychological stressors• Environment: social,political,economic,housing,etc• Vector:insects, mosquits

Risk factors(BEINGS)• Biologic (gender, age, wt ,bone density) and

behavioral(smoking,sexual,ETOH abuse,illegal drug use

• Environmental: e.g aircondition—legionaires dse,Lyme dse—env suitable for tick

• Immunological—small pox-eradicated(vaccine & herd immunity)

• Nutritional—Japanese-American (MI),Burkitt—dietary fibres,Framingham study—high lipid—MI

• Genetic factors:population genetics & genetic epidemiology—genetic screening—PKU

• Services,social factors,spiritual factors:

Ecologic issues in epidemiology

• People are seen not only as individuals but members of communities in asocial context

• Any action in eco system—reaction(+ve/-ve)

• As one factor in eco systems changed—inevitably change others

• Examples:reduction of mortality in childhood—increased prevalence of DJD,control of inf dse—increase of another set of dses

Vaccination and patterns of immunity

• Herd immunity--?• Vaccination program?• Diphteria—vaccine produced immunity is

different now from years ago(natural dse--subclinical booster dose)now more susciptable

• Diphteria epidemic in NIS of soviet union 1990

vaccination

• Smallpox: eradication vaccination(variola major,and variola minor) ? Risk

• Poliomyelitis:salk1950’s(injectable)—no herd immunity.sabin(oral)1960’s—herd immunity--?eradication.

• Palestine(Gaza) salk followed by sabin?• Wild paralytic polio eradicated,only vaccine paralytic

polio (USA)—switch to salk• Syphilis:1ry & 2ry stages—herd immunity,partial

individual immunity,still pt—goes to latent-3ry stage,abx tx quick response ,but reinfection is v high

Sanitation• 19th century—killers—diarheal(children) and T. B(adults)• Sanitation--↓inf mortality rate--↑pop growth• Demographic gap—difference between birth and death rates• ↓inf mortality rate-cause for pop growth and necessity for pop

control• Sanitation—affects dse pattern—e.g appearnce of epidemic

paralytic polio—(iceberg phenomenon) by decreasing exposure of newborns to subclinical infection—delaying inf to childhood(no longer protected by maternal immunity—upper socioeconomic group –most suffered

• Similar is Hep A virus(fecal oral route)—delay of inf to adulthood

Vector Control and land use patterns

• Subsaharan africa –e.g.of negative effects of good act.

• Tse Tse fly control—larger # of cattle—overgrazing—frequent droughts

River dam construction and patterns of dse

• Aswan dam --↑# of ?

• Senga river project-- ↑# of malaria,Rift valley fever, and Denge fever,and schistomiasis

• Why?

Synergism of factors predisposing to dse• STD’s--++HIV—AIDS—reactivation of

latent inf e.g. T.B.

• Malnutrition and infection(vicious circuit)

• Ecological and genetic factors—new strains of influenza(antigenic shift,antigenic drift)

Uses

• Population or community health assessment

• Individual decisions

• Completing the clinical pictureCompleting the clinical picture

• Search for causes