EPIDEMIOLOGICAL APPLICATIONS IN CHN PRESENTING BY: DR/AMIRA YAHIA

DEFINITION OF EPIDEMIOLOGY Epidemiology is the study of the distribution and determinants of health and disease in human populations, and is the principal science of community health practice.

Cont…. Community health nurses use epidemiological concepts to improve the health of population groups by identifying risk factors and optimal approaches that reduce disease risk. Epidemiological methods are important for accurate community assessment and diagnosis and in planning and evaluating effective community interventions

USES OF EPIDEMIOLOGY IN DISEASE CONTROL AND PREVENTION 1. Identifying characteristics of people who suffered from a disease such as cholera or plague and compared them with characteristics of those who are healthy such as personal factors, socioeconomic status and health status

Cont…. 2. Questioning whether there were differences in the location or living environment of ill people compared with healthy individuals and whether these factors influenced disease development 3. Examining whether common time factors existed (i.e., when people acquired disease)

EPIDEMILOGICAL METHODS 1.Descriptive epidemiology : Descriptive Epidemiology focuses on the amount and distribution of health and health problems within a population. Its purpose is to describe the characteristics of people who are protected from disease and those who have a disease.

Cont…. Factors of particular interest include age, sex, ethnicity or race, socioeconomic status, occupation and family status. Epidemiologists use morbidity and mortality rates to describe the extent of disease and to determine the risk factors that make certain groups prone to acquiring disease.

2. Analytic Epidemiology: Analytic Epidemiology investigates the causes of disease by determining why a disease rate is lower in one population group than in another. This method tests hypothesis generated from descriptive data and either accepts or rejects them on the basis of analytic research. The epidemiologist seeks to establish a cause and effect relationship between preexisting condition or event and the disease.

EPIDEMIOLOGICAL TRIANGLE MODEL Is the examination of the interrelationships between host and environmental characteristics and uses an organized method of injury to derive an explanation of disease. In this model the epidemiologist must analyse the following three elements: agent, host and environment

Cont….. The development of disease is dependent upon: a. The strength of the agent b. The host’s genetic or immunological susceptibility c. The environmental conditions existing at the time of exposure, which includes the biological, social, political and physical environment.

Cont….. The model implies that the rate of disease will change when the balance among these three factors is altered. By examining each of the three elements, a community health nurse can methodically assess a health problem, determine protective factors and evaluate the factors that make the host vulnerable to disease.

Epidemiological Triangle Host Environment Agent

Cont…. In studying chronic diseases, epidemiologists use methods that are similar to those used in infectious disease investigation, thereby developing theories about chronic disease control. Risk factor identification is of particular importance to chronic disease reduction

RISK FACTORS Risk factors variables that increase the rate of disease in people who have them (e.g., a genetic predisposition) or in those exposed to them (e.g., an infectious agent or a diet high in saturated fat). Therefore their identification is critical to identifying specific prevention and intervention approaches that effectively and efficiently reduces chronic disease morbidity and mortality.

Cont…. For example, the identification of cardiovascular disease risk factors has suggested a number of lifestyle modifications that could reduce the morbidity risk before disease onset. Primary prevention strategies such as dietary saturated fat reduction, smoking cessation and hypertension control developed in response to previous epidemiological studies that identified these risk factors.

CALCULATION OF RATES The community health nurse must analyze data about the health of the community determine the pattern of disease in a community. The nurse may collect data by conducting surveys or compiling data from existing records (e.g., data from clinic facilities or vital statistics records). Often assessment data are in the form of counts or simple frequencies of events (e.g., the number of people with a specific health condition). Community health nurse interpret these raw counts by transforming them into rates.

RATES: Rates are arithmetic expressions that help nurses consider a count of an event relative to the size of the population from which it is extracted (e.g., the population at risk). When raw counts are converted to rates, the community health nurse can make meaningful comparisons with rates from other countries, from the nation and from previous time periods.

Cont…. These analyses assist the nurse in determining the magnitude of a public health problem in a given area and allow more reliable tracking of trends in the community over time

MORBIDITY RATES OF ILLNESS 1. Incidence Rate Incidence rates describe the occurrence of new cases of a disease or condition (e.g., teen pregnancy) in a community over a period of time relative to the size of the population at risk for that disease or condition during that same time period. The incidence rate may be the most sensitive indicator of the changing health of a community because it captures the fluctuations of disease in a population

2. Prevalence Rate Is the number of all cases of a specific disease or condition (e.g., deafness) in a population at a given point in time relative to the population at the same point in time. Morbidity rates are not available for many conditions because surveillance of many chronic diseases is not widely conducted. Furthermore, morbidity rates may be subject to underreporting when they are available. Routinely collected birth and death rates, or mortality rates, are more widely available.

OTHER RATES 1. Crude rates (Basic, rough Rates) Summarize the occurrence of births (i.e., crude birth rate), mortality (i.e., crude death rates), or diseases (i.e. crude disease rates), in the general population. Age specific rates characterize a particular age group in the population and usually consider deaths and births. Determining the rate for specific subgroups of a population and using a denominator that reflects only that subgroup removes age bias.

a. Crude birth rate = number of live births during the year/average (midyear) population Per 1000 population b. Crude death rate = number of deaths during the year/average (midyear) population Per 1000 population c. Age-specific death rate = number of deaths among people of a given age group in one year/average (midyear) population in specified age group Per 1000 population d. Cause-specific death rate = number of deaths from a stated cause in one year/average (midyear) population Per 100,000 population

USE OF EPIDEMIOLOGY IN DISEASE PREVENTION 1. Primary Prevention The central goals of epidemiology are: a. Describing the disease patterns b. Identifying the etiologic factors in disease development c. Finding the most effective preventive measures. When these measures occur before disease development, they are called primary prevention. Primary prevention relies on epidemiological information to indicate those behaviors that are protective, or will not contribute to an increase in disease, and those that are associated with increased risk.

2. Secondary and Tertiary Prevention Secondary prevention occurs after pathogenesis. Those measures designed to detect disease at its earliest stage, namely screening and physical examinations that are aimed at early diagnosis, are secondary prevention. Interventions that provide for early treatment and cure of disease are also in this category. Tertiary prevention includes the limitation of disability and the rehabilitation of those with irreversible disease such as diabetes and spinal cord injury.

ESTABLISHING CAUSALITY A principal goal of classic epidemiology is to identify etiologic factors of diseases to encourage the most effective primary prevention activities. The following six criteria establish the existence of a cause and effect relationship:

Cont… 1. Strength of association: Rates of morbidity or mortality must be higher in the exposed group than in the non-exposed group. Relative risk ratios or odds ratios, and correlation coefficients indicate whether the relationship between the exposure variable and the outcome is causal.

Cont… For example, epidemiological studies demonstrated an elevated relative risk for heart disease among smokers compared with nonsmokers.

2. Dose-response relationship: An increased exposure to the risk factor causes a concomitant increase in disease rate. The risk of heart disease mortality is higher for heavy smokers compared with light smokers. 3. Temporally correct relationship: Exposure to the causal factor must occur before the effect or disease. For heart disease, smoking history must precede disease development

4. Biological plausibility: The data must make biological sense and represent a coherent explanation for the relationship. Nicotine and other tobacco-derived chemicals are toxic to the vascular endothelium. In addition to raising low-density lipoprotein (LDL) and decreasing high-density lipoprotein (HDL) cholesterol levels, cigarette smoking causes arterial vasoconstriction and platelet reactivity, which contributes to platelet thrombus formation

5. Consistency with other studies: Varying types of studies in other populations must observe similar associations. Numerous studies of different designs have repeatedly supported the relationship between smoking and heart disease. 6. Specificity: The exposure variable must be necessary and sufficient to cause disease; there is only one causal evidence, this criterion is less important today. Diseases do not have single causes; they have multi-factorial origins.

SCREENING The purpose of screening programs is to identify risk factors and diseases in their earliest stages. Screening is usually a secondary prevention activity because disease appears after a pathological change has occurred or ideally, early in the disease process.

SURVEILLANCE In addition to screening, surveillance is a mechanism for the ongoing collection of community health information. Monitoring for changes in disease frequency is essential to effective and responsive public health programs.

Cont…. Identifying trends in disease incidence or identifying risk factor status by location and population subgroup over time allows the community health nurse to evaluate the effectiveness of existing programs and implement interventions targeted to high-risk groups.

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