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nApplied Epidemiology
Introduction
The main goals of vet. Services are:
ü Health protection and maintenance.
ü Animal production.
Animal health programmes:
Animal health programmes assess:
The present situation in livestock production and future needs.
The effect disease is having on the present situation and in the future.
The potential for intervention in animal health, the resources available, and the interventions that are technically possible.
Planning for livestock programme:
Several steps are involved in this stage:
Give goals and objectives.
Resources and approaches available to deal with the disease.
A rough design should be made covering technical, social, organization, economic etc ..
A final design then will be made.
Programme implementation, monitoring, control and evaluation:
The problem of project should be considered at time zero at the start of evaluation.
The monitoring and control activities carried out during this stage enable the necessary adjustments to be made in the project design as the project progresses.
The information generated from these activities will provide feedback to all levels of the planning progress and will also be used in the final evaluation of the project once it has ended or a particular phase has been completed.
n The Role of various disciplines in the planning process
ü The specific disciplines that are essential to the understanding of the animal health problems (epidemiology and animal production).
ü In the following figure it is clear the inter- disciplinary approach involving the close and continuous cooperation of the various disciplines concerned.
n The major disciplines involved in the planning
and Evaluation of animal health programmes
n The main difficulties in such programmes are the coordination and cooperation between the different departments.
n The two points should be considered are:
ü Planning and evaluation of animal health programmes require a clear understanding of both the epidemiology of the diseases in question and the livestock production system involved.
ü The availability of reliable and up-to-date information at all stages of planning and evaluation process.
n What is the Epidemiology ?
Epidemiology is the study of the distribution, frequency and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems.
This is emphasizes that epidemiologists are concerned not only with death, illness and disability but also with more positive health states and with the means to improve health.
n Some basic epidemiological concepts:
n It is known that epidemiologists are interested in studying diseases in populations.
n Epidemiologist determines What, When, Where, Who, and Why. However, the epidemiologist is more likely to describe these concepts in slightly different terms: case definition, time, place, person, and causes.
ü Epidemiology is data-driven and relies on a systematic and unbiased approach to the collection, analysis, and interpretation of data.
ü Basic epidemiologic methods tend to rely on careful observation and use of valid comparison groups to assess whether what was observed, (such as the number of cases of disease in a particular area during a particular time period or the frequency of an exposure among animals with disease), differs from what might be expected.
The following points were considered:
n Population
n Population at risk: the part of a population which is potentially susceptible to a disease under consideration.
n The interaction of a large number of different factors ( host, causative agent and environmental factors).
n Uses of Epidemiology
ü Assessing the population’s health.
ü Making individual decisions.
ü Completing the clinical picture.
ü Searching for causes
n Epidemiology Tasks
In the mid-1980s, five major tasks of epidemiology in public and animal health practice were identified:
Public and animal health surveillance.
Field investigation.
Analytic studies.
Evaluation: is the process of determining, as systematically and objectively as possible, the relevance, effectiveness, efficiency, and impact of activities with respect to established goals.
Linkages: During an investigation an epidemiologist usually participates as either a member or the leader of a multidisciplinary team. Other team members may be laboratorians, sanitarians, infection control personnel or other clinical staff, local, state, or federal levels of government, academic institutions, clinical facilities, or the private sector and, increasingly, computer information specialists.
A sixth task, policy development, was recently added.
n Types of epidemiological studies
• Prospective study
ü Look forward over period of time and examine associations between determinants and the frequency of occurrence of a disease in groups.
ü Called cohort studies. For high incidence diseases.
n Types of epidemiological studies
2 . Retrospective studies
ü Look backward over period of time and compare associations between determinants and the frequency of occurrence of a disease in groups diseased and non diseased individuals.
ü Called case – control studies, Cheap, can make use of present data, can be used for diseases of low incidence occurrence
n Types of epidemiological studies
3. Cross – sectional studies
ü Which is attempt to examine and compare estimated of disease prevalence between various population at particular period of time.
ü They are called surveys. They are carried in a limited time period, detecting prevalence rate in different populations, the effect of different determinants on disease prevalence.
n Important epidemiological definitions
• Endemic: a persistent level of occurrence with a low to moderate disease level.
• Sporadic: an irregular pattern of occurrence, with occasional cases occurring at irregular intervals.
• Epidemic\ Epizootic\ Outbreak: when occurrence of a disease within an area is clearly in excess of the expected level for a given time period.
• Pandemic: it is spread of an epidemic over several countries or continents, affecting a large number of animals.
n FREQUENCY MEASURES OF RISK
Incidence, prevalence, and mortality rates are three basic frequency measures that are used to characterize the occurrence of health events in a population.
Incidence:
Refers to the occurrence of new cases of disease or injury in a population over a specified period of time. Although some epidemiologists use incidence to mean the number of new cases in a community, others use incidence to mean the number of new cases per unit of population.
n We use incidence rates instead of raw numbers for comparing disease occurrence in different populations because rates adjust for differences in population sizes.
Prevalence:
The term “disease prevalence” refer specifically to all current cases (new and old) existing at a given point in time. Or over a period of time in a given population. The total number of all individual who have attribute or disease at a particular time (or during a particular period) divided by a population at risk of having attribute or disease at this point of time or midway through the period. Prevalence rate is really a ratio.
Method for calculating prevalence of disease
All new and pre-existing cases
during a given time period
x100
Population during the same time period
Mortality rate
A mortality rate is a measure of the frequency of occurrence of death in a defined population during a specified interval. Morbidity and mortality measures are often the same mathematically; it’s just a matter of what you choose to measure, illness or death.
The formula for the mortality of a defined population, over a specified period of time, is:
Deaths occurring during a given time period
x10ⁿ
Size of the population among which
the deaths occurred
n= 1000 or 100,000
Case-fatality rate
The case-fatality rate is the proportion of persons with a particular condition (cases) who die from that condition.
It is a measure of the severity of the condition.
The formula is:
Number of cause-specific deaths among the
incident cases
x10ⁿ
Number of incident cases
n=100 (percentage)
n In 1989, 733,151 new cases of gonorrhea were reported among the United States civilian population. The 1989 mid-year U.S. civilian population was estimated to be 246,552,000. calculate incidence.
§ In a survey of workers at Khartoum teaching hospital, 180 of 300 workers interviewed reported use of personal protection equipment (gloves) at least once during the 2 months before the interview.
n A total of 2,123,323 deaths were recorded according to influenza infection in 1987. The mid-year population was estimated to be 243,401,000 . calculate mortality rate.
n two died of the 11 neonates who developed listeriosis,. calculate The case-fatality rate.
منتصر محمد عبدالله
السودان / نهر النيل / شندي
ساحة النقاش