Scope of Epidemiology-2

Types of Epidemiological Investigations:

There are four approaches to epidemiological investigation

• Descriptive epidemiology
• Analytical epidemiology
• Experimental epidemiology
• Theoretical epidemiology

Descriptive epidemiology

Descriptive epidemiology involves observing and recording diseases and possible causal factors. “First part of an investigation” Observations may generate hypotheses that can be tested more rigorously later.

Analytical epidemiology

Analytical epidemiology is the analysis of observations using suitable diagnostic and statistical procedures.

Experimental epidemiology

• Experimental epidemiologists observe and analyze data from groups of animals from which they can select, and in which they can alter, the factors associated with the groups
• An important component of the experimental approach is the control of the groups
• Use of laboratory animals whose short lifespan enable events to be observed more rapidly than in humans

Theoretical epidemiology

Theoretical epidemiology consists of the representation of disease using mathematical ‘models’ that attempt to simulate natural patterns of disease occurrence. 

Epidemiological subdisciplines:

There are various epidemiological subdisciplines

Clinical epidemiology

Clinical epidemiology is the use of epidemiological principles, methods and findings in the care of individuals, with particular reference to diagnosis and prognosis.

Computational epidemiology

• Application of computer science to epidemiological studies
• Representation of disease by mathematical models
• Use of expert systems (Formulating disease control strategies, predicting animals productivity Supporting management decisions)

Genetic epidemiology

• Genetic epidemiology is the study of the cause, distribution and control of disease in related individuals, and of inherited defects in populations. Also explore Interactions between genetic and non-genetic factors.

Field epidemiology

• Field epidemiology is a timely, judgmental process based on description, analysis, common sense and the need to design practical control policies
• When outbreaks of foot-and –mouth disease occur, field epidemiologists promptly trace potential sources of infection in an attempt to limit spread of the disease.

Participatory epidemiology

• 1980 with development of veterinary services, animals were economically and socially important, use of local knowledge to gain information, with the main goal of improving animal health
• Techniques that are employed evolved in the social science, and consist of simple visual methods and interviews to generate qualitative data
• “Participatory epidemiology” it is a tool for the field epidemiologist, which is increasingly used in developing counties. Is concerned with local knowledge of, and practices relating to, the health of animals

Molecular epidemiology

• Study of small genetic and antigenic differences between viruses and other microorganisms at a higher level of discrimination
• The methods include peptide mapping, nucleic acid ‘fingerprinting’ and hybridization, restriction enzyme analysis, monoclonal antibodies and the polymerase chain reaction
• Nucleotide sequencing of foot-and–mouth  that some outbreaks of the disease involved vicinal strains, suggesting that improper inactivation or escape of virus from vaccine production plants. Unrestricted animals movement is a major factor in dissemination of the disease in West Africa.

Environmental Epidemiology:

• Concerned with the relationship between disease and environmental factors such as industrial pollution and occupational hazards

Micro-Epidemiology:

• Study of disease in a small group of individuals with respect to factors that influence its occurrence in larger segments of the population

Macro-Epidemiology:

Study of national patterns of disease, and the social, economic and political factors that influence them

Chronic disease epidemiology

Nutritional epidemiology

Subclinical epidemiology

Social epidemiology

Psychosocial epidemiology

Components of epidemiology:

The first stage in any investigation is the collection of relevant data. Investigations can be either qualitative or quantitative or a combination of these two approaches.

• Qualitative investigations
• Quantitative investigations

Qualitative investigations

• The natural history of disease
• The ecology of diseases, including the distribution, mode of transmission and maintenance of infectious diseases, is investigated by field observation. Field observations also may reveal information about factors that may directly or indirectly cause disease.
• Causal hypothesis testing
• If filed observations suggest that certain factors may be causally associated with a disease, than the association must be assessed by formulation a causal hypothesis

Quantitative investigations

• Quantitative investigations involve measurement (e.g., the number of cases of disease), and therefore expression and analysis of numerical values. Quantitative investigations include surveys, monitoring and surveillance, studies, modeling, and the biological and economic evaluation of disease control. Walls of the research organization- ‘armchair epidemiology’

Surveys

• A survey is an examination of an aggregate of units.       
• Surveys can be undertaken on a sample of the population.
• A census, a cross-sectional survey records events occurring at a particular point in time.
• A longitudinal survey records events over a period of time. Prospectively form the present into the future; on may be a retrospective record of past events. 
• In epidemiological surveys, characteristics might include the presence of particular diseases, or production parameters such as milk yield.

Screening

• A particular type of diagnostic survey is screening. Identification of undiagnosed cases of disease using rapid tests or examination
• Screening tests are not intended to be diagnostic; individuals with positive test results (i.e., that are classified as diseased by the screening test) usually require further investigation for definite diagnosis. They therefore differ from diagnostic tests.
• Screening involves investigation of the total population (mass screening). Targeted at animals only in areas where there have been cases of disease (strategic screening). Prescriptive screening aims at early identification of diseases that can be controlled better if they are detected early in their pathogenesis.

Monitoring and surveillance

• Monitoring is the making of routine observations on health, productivity and environmental factors and the recording and transmission of these observations.
• Recording of milk yields or routine recording of meat inspection findings at abattoirs
• Surveillance is a more intensive form of data recording than monitoring. Used to describe the tracing and observation of people who were in contact with cases of infectious disease Include all types of disease – infectious and non-infectious 
• It is normally part of control programmes for specific diseases.

Studies

There are four main types of epidemiological study:

• Experimental studies;
• Cross-sectional studies;
• Case-control studies;
• Cohort studies

Modelling

Using mathematical equations ‘Modelling’

Risk assessment

Evaluation of the risk of the occurrence of adverse, development of formal methods of quantitative and quantitative risk assessment e.g. Microbiological risk assessment with food safely risks, and estimation of the magnitude of microbial exposure at various stages in the production chain (rearing on the farm; transport and processing; retail and storage; preparation) to campylobacter spp and salmonella spp.

Disease control

The goal of epidemiology is to improve the veterinarian's knowledge so that diseases can be controlled effectively, and productivity thereby optimized. This can be fulfilled by treatment, prevention or eradication