Epidemiology is the systematic, objective study of the natural history of disease within populations and the factors that determine the spread of disease. This is one of the scientific theoretical foundations of public health.
The identification of risk factors is vital for public health Ancient Times: Hippocrates (460 to 375 BC) Middle Ages:1348 - Plague (“Black Death”) 18th century: Florence Nightingale (1820–1910) 19th century: Modern epidemiology (see Table 8-1) Causal thinking Sanitary statistics Infectious-disease epidemiology Chronic-disease epidemiology Current: Eco-epidemiology- an integrative approach Epidemiologists consider multiple levels of causation Epidemiologists investigate the interplay between genetic and environmental factors epidemiologists increasingly recognize the enrichment that follows from examining the trajectory of health and illness over the life- reflect earlier live experiences Taking a systems or wholes view: Investigators are now demonstrating that methods developed for infectious diseases-such as modeling transmission of epidemics across and within populations-are relevant for noninfectious diseases and behaviors.
Host Susceptible human or animal who harbors and nourishes a disease-causing agent Agent A factor that causes or contributes to a health problem or condition Environment All the external factors surrounding the host that might influence vulnerability or resistance
Relationship between a cause and its effect Chain of causation Causation in noninfectious disease: environmental exposure and potential health outcomes (9 elements) Multiple causation Dever’s epidemiological model, also called the web of causation
Immunity: A host’s ability to resist a particular infectious disease-causing agent Passive immunity: short-term; acquired naturally or artificially Active immunity: long-term, sometimes lifelong; acquired naturally or artificially Cross-immunity: immunity to one agent providing immunity to another related agent Herd immunity: immunity level present in a population group Risk Probability that a disease or unfavorable health condition will develop Directly influenced by biology, environment, lifestyle, and system of health care. Risk factors: negative influences Epidemiologists studying populations at risk: collection of people among whom a health problem has the possibility of developing because certain influencing factors are present or absent or because there are modifiable risk factors Measurement of relative risk ratio: incidence rate in exposed group/incidence rate in unexposed group
From Textbook Susceptibility stage Subclinical disease stage Incubation period Induction period Clinical disease stage Resolution stage
Descriptive epidemiology Counts Rates Incidence : refers to all new cases of a disease or health condition appearing during a given time Number of persons developing a disease Total number at risk per unit of time Prevalence : all of the people with a particular health condition existing in a given population at a given point in time Number of persons with a characteristic Total number in population Computing rates Mortality Morbidity Analytic epidemiology Prevalence studies Case-control studies Cohort studies Experimental epidemiology
July 2010 CDC estimates that more than one million people are living with HIV in the United States. One in five (21%) of those people living with HIV is unaware of their infection. Despite increases in the total number of people living with HIV in the US in recent years, the annual number of new HIV infections has remained relatively stable. However, new infections continue at far too high a level, with an estimated 56,300 Americans becoming infected with HIV each year. More than 18,000 people with AIDS still die each year in the US. Gay, bisexual, and other men who have sex with men (MSM) † are strongly affected and represent the majority of persons who have died. Through 2007, more than 576,000 people with AIDS in the US have died since the epidemic began.
Race/Ethnicity: Black, Hispanic/Latino
World population estimated to be 7 billion 2011 Demography: The study of the characteristics of human populations, such as size, growth, density, distribution, and vital statistics.
Direct transmission: occurs by immediate transfer of infectious agent from a reservoir to a new host- HIV Indirect transmission: occurs when the infectious agent is transported within contaminated inanimate materials such as air, water, or food (vehicle-borne transmission)- Cholera, Typhoid Vector transmission: occurs when infectious agent is carried by a vector (nonhuman carrier such as an animal or insect)- Malaria Airborne transmission: occurs through droplet nuclei—the small residues that result from evaporation of fluid from droplets emitted by an infected host- TB
Primary Education Use of mass media Targeting meaningful health messages to aggregates Immunization Vaccine-preventable diseases and schedule Assessing immunization status of community (possible barriers); planning and implementing immunization programs adult immunizations Secondary prevention Screening Case and contact investigation, partner notification Tertiary prevention Isolation and quarantine Control transmission by health care workers Safe handling and control of infectious wastes
Anthrax Acute bacterial disease that affects mainly the skin (cutaneous) or respiratory tract (inhalation) Case fatality: 5–20% for cutaneous, 100% for inhalation Smallpox Variola virus transmitted person to person Risks associated with smallpox vaccination
WHO’s three-pronged approach: Case finding Surveillance and control Elimination and eradication
Assessment: case identification, case finding; comprehensive; no assumptions; community’s need for surveillance or new/improved control programs Planning: assisting with immunizations, symptom relief, controlling disease if present, limiting exposure, collaboration Implementation: service delivery; supervision of staff; agency functions; primary prevention education for future infections; recordkeeping and reporting Evaluation
NURS 348l Public Health Nursing Chapter 7 Epidemiology in Community Health Care H Harris, 2011
Methods in Epidemiological Investigative Process <ul><ul><li>Descriptive epidemiology </li></ul></ul><ul><ul><ul><li>Counts </li></ul></ul></ul><ul><ul><ul><li>Rates </li></ul></ul></ul><ul><ul><ul><ul><li>Incidence : </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Number of persons developing a disease Total number at risk per unit of time </li></ul></ul></ul></ul><ul><ul><ul><li>Prevalence : </li></ul></ul></ul><ul><ul><ul><li>Number of persons with a characteristic </li></ul></ul></ul><ul><ul><ul><ul><li>Total number in population </li></ul></ul></ul></ul><ul><ul><li>Computing rates </li></ul></ul><ul><ul><ul><li>Mortality </li></ul></ul></ul><ul><ul><ul><li>Morbidity </li></ul></ul></ul><ul><ul><li>Analytic epidemiology </li></ul></ul><ul><ul><li>Experimental epidemiology </li></ul></ul>H Harris, 2011
Sources of Epidemiologic Information <ul><ul><li>Vital statistics </li></ul></ul><ul><ul><li>Census data </li></ul></ul><ul><ul><li>Reportable diseases </li></ul></ul><ul><ul><li>Disease registries </li></ul></ul><ul><ul><li>Environmental monitoring </li></ul></ul><ul><ul><li>National Center for Health Statistics health surveys </li></ul></ul><ul><ul><li>Informal observational studies </li></ul></ul><ul><ul><li>Scientific studies </li></ul></ul>H Harris, 2011
HIV in the United States Incidence and Prevalence, US 1977-2006 H Harris, 2011 http://www.cdc.gov/hiv/resources/factsheets/us.htm
HIV Incidence & Prevalence <ul><li>Gay, Bisexual, and Other Men Who Have Sex with Men (MSM) </li></ul><ul><li>Heterosexuals and Injection Drug Users </li></ul><ul><li>Race/Ethnicity </li></ul><ul><li>Risk Groups </li></ul><ul><li>Incidence </li></ul>H Harris, 2011 http://www.cdc.gov/hiv/resources/factsheets/us.htm