Epidemiology in Community Health Care Chapter 7 Epidemiology in Community Health Care

Objectives: Upon mastery of this chapter, you should be able to: Explore the historical roots of epidemiology. Explain the host, agent, and environment model. Describe theories of causality in health and illness. Explain a “web of causation” matrix that assists you with recognition of multicausal factors in disease or injury occurrences.

Objectives: Define immunity and compare passive immunity, active immunity, cross-immunity, and herd immunity. Explain how epidemiologists determine populations at risk. Identify the four stages of a disease or health condition. List the major sources of epidemiologic information.

Introduction In this unit, the focus is on epidemiology, communicable disease control, and environmental health and safety. These are cornerstone areas of public health practice and are just as important at the local level as at the regional, national, and international levels.

Definition of health The World Health Organization (WHO) defines the health as “ a state of complete well-being, physical, social, and mental, and not the absence of diseases …. 1988

Definition of Epidemiology Epidemiology :is the study of distribution and determine of health-related states or events in specific populations, and the application of this study to control of health problems

What is Epidemiology? Science of Public Health that studies: Distribution of disease Determinants of health/disease Specific populations Look for patterns of disease Time, place, personal characteristics Interventions Prevention is key

What does Epidemiology study? Health-related Infectious disease Chronic disease

Historical Roots of Epidemiology Ancient Times: Hippocrates, Greek physician 460 to 375 BC Middle Ages: 1348: Plague (Black Death) 18th century: Florence Nightingale (1820–1910) 19th century: modern epidemiology sanitary statistics infectious-disease epidemiology chronic-disease epidemiology

Epidemiologic Information 1) Case definition 2) Person 3) Place 4) Time

1) Case Definition Standard set of criteria Clinical and lab Allows for comparison

Case Definition example : Smallpox Clinical Description An illness with acute onset of fever >101 °F followed by a rash characterized by vesicles or firm pustules in the same stage of development without other apparent cause. Laboratory Criteria for Confirmation Isolation of smallpox (variola) virus from a clinical specimen, or

Case Definition Gradient High Specificity Low Specificity Suspected Probable Confirmed

2) Person Age Sex Race/Ethnicity Socio-Economic Status Behaviors

3) Place Geographic Distribution Natural Clustering vs. uniform Home Work School Hospital room

Regional HIV and AIDS statistics and features, 2006 TOTAL North America Eastern Europe & Central Asia Latin America South and South-East Asia Sub-Saharan Africa Oceania Western & Central Europe Caribbean East Asia Middle East & North Africa 18 000 [11 000 – 26 000] 84 000 [58 000 – 120 000] 65 000 [51 000 – 84 000] 590 000 [390 000 – 850 000] 2.1 million [1.8 – 2.4 million] 270 000 [170 000 – 820 000] 2.9 million [2.5 – 3.5 million] 0.8% [0.6% – 1.1%] 0.9% [0.6% – 1.4%] 0.5% [0.4% – 1.2%] 0.6% [0.4% – 1.0%] 5.9% [5.2% – 6.7%] 1.0% [0.9% - 1.2%] 4.3 million [3.6 – 6.6 million] 43 000 [34 000 – 65 000] 140 000 [100 000 – 410 000] 860 000 [550 000 – 2.3 million] 2.8 million [2.4 – 3.2 million] 4000 [2300 – 6600] 12 000 [ <15 000] 19 000 [14 000 – 25 000] [26 000 – 64 000] 36 000 [20 000 – 60 000] 0.4% [0.2% – 0.9%] 0.3% [0.2% – 0.4%] 1.2% [0.9% – 1.7%] 0.1% [<0.2%] 0.2% [0.1% – 0.3%] 7100 [ 3400 – 54 000] 22 000 [18 000 – 33 000] 27 000 [20 000 – 41 000] 100 000 [56 000 – 300 000] 68 000 [41 000 – 220 000] Adult & child deaths due to AIDS Adult (15‒49) prevalence [%] Adults & children newly infected with HIV Adults & children living with HIV 24.7 million [21.8 – 27.7 million] 39.5 million [34.1 – 47.1 million] 1.4 million [880 000 – 2.2 million] 1.7 million [1.2 – 2.6 million] [1.3 – 2.5 million] 7.8 million [5.2 – 12.0 million] 81 000 [50 000 – 170 000] 740 000 [580 000 – 970 000] 250 000 [190 000 – 320 000] 750 000 [460 000 – 1.2 million] 460 000 [270 000 – 760 000] Regional HIV and AIDS statistics and features, 2006 Table b

Geographic Distribution

4) Time Onset of symptoms Incubation Period Infectious Period Seasonality Baseline vs. epidemic Interval Long-term trends Shorter for environmental exposure

Mortality versus Morbidity rate Mortality rate : is a measure of the number of deaths (in general, or due to a specific cause) in some population, scaled to the size of that population, per unit time. * Morbidity rate : refers to the number of individuals who have contracted a disease during a given time period

Examples : *Mortality rate : Ex. Number of deaths from TB is 39 per 10 100000 population in KSA. *Morbidity rate : Ex.: the number of HIV cases is 432 per 100000 population in South Africa.

Epidemiologic Triangular: Host, Agent, & Environment susceptible human or animal who harbors and nourishes a disease-causing agent 2)Agent a factor that causes or contributes to a health problem or condition 3)Environment all the external factors surrounding the host that might influence vulnerability or resistance

Epidemiologic Triangular

Epidemiologic Triangular

Theories of Causality in Health and Illness Relationship between a cause and its effect 1) Chain of Causation:

Chain of Infection

Web of Causation: Infant Mortality 2) Multiple Causation:

Transmission b) Indirect a) Direct Portal of Entry Portal of Exit Airborne Vehicle Vector Mechanical vs. biologic a) Direct Contact Droplet Portal of Entry Portal of Exit

Definition & Types of Immunity A host’s ability to resist a particular infectious disease–causing agent. Acquired immunity: is the resistance acquired by a host as a result of previous natural exposure to infectious agent Ex. : having a measles once protects against future infection * Acquired immunity may be induced by active or passive immunity

Types of immunization : 1- Active immunity: refers to immunization of an individual by administration of an antigen (infectious agent or vaccine ) and usually characterized by the presence of an antibody produced by the individual host *long-term immunization Ex.: vaccination of the children against measles .

Types of immunization : 2- Passive immunity: refers to immunization through the transfer of specific antibody from an immunized individual to no immunized individual . * short-term immunization. Ex .: used of immunoglobulin to hepatitis patient .

Populations at Risk The risk of developing a health problem is directly influenced by their biology, environment, lifestyle, and system of health care.

Four Stages of a Disease or Health Condition

Major Sources of Epidemiologic Information Existing Data Vital Statistics Census Data Reportable Diseases Disease Registries Environmental Monitoring Informal Observational Studies Scientific Studies

Incidence rate Incidence rate: Number of new disease cases per population at risk High incidence implies high disease occurrence Low incidence implies low disease occurrence Measured over a given time interval Usage: 1-Determine probability of developing a specific disease 2-Used to detect etiologic factors refers to all new cases of a disease or health condition appearing during a given time.

Incidence rate formula : Ex.: the number of people age 30-39 at risk at 10,000, since all the time new people are entering the population at risk ( 100 cases ) Number of persons developing a disease x100% Total number

Summary Case definition, person, time, place Know disease/agent Triangular epidemiology Passive and active immunization Incidence rate calculation