1. Epidemiology – Epidemiology is the study of the distribution and determinants of health-related states or events (including disease), and the application of this study to the control of diseases and other health problems. Various methods can be used to carry out epidemiological investigations: surveillance and descriptive studies can be used to study distribution; analytical studies are used to study determinants.
2. Uses of epidemiology – The major uses of epidemiology are:
a. To assess the magnitude or burden of disease in a community. It, therefore, helps in studying the occurrence of disease ina population.
B. To assess the health status of communities. It, therefore, helps in establishing a community diagnosis.
c. To search for determinants of disease. To find out how and why disease is caused is a major use of epidemiology.
d. To estimate an individual’s risks and chances of suffering from a disease and to establish the prognosis in an individual suffering from disease.
e. To plan comprehensive health services, including specific strategies and ways and means of implementation.
f. To evaluate strategies and interventions for disease control. Such evaluation helps in identifying weaknesses and tosuggest remedial measures for the future. Evaluation of costs and benefits or effectiveness of specific interventions is also anintegral use.
g. To complete the natural history of disease. In a hospital setting only the terminal cases are seen and how disease starts and presents in its initial stages is only possible by studying disease in the community.
h. To forecast future disease trends.
i.To identify syndrome
3. Epidemiological triad - disease caused by an interaction between agents host and environmental characters when all three are in harmony health is insured what maladjustment in their relationships leads to disease. The three factors together constitute the epidemiological triad.
4. Retrospective studies - A retrospective study looks backwards and examines exposures to suspected risk or protection factors in relation to an outcome that is established at the start of the study.Most sources of error due to confounding and bias are more common in retrospective studies than in prospective studies. For this reason, retrospective investigations are often criticised.
5. Prospective studies - A prospective study watches for outcomes, such as the development of a disease, during the study period and relates this to other factors such as suspected risk or protection factor(s). The study usually involves taking a cohort of subjects and watching them over a long period.
6. Case control study - case control study is an epidemiological study where a group of individuals with disease are compared with a group of individuals who are not suffering from disease in terms of specific disease causing exposure. since the starting point is a group of people who already have suffered from the disease this is labelled as a retrospective study.
Advantages of case control studies
-relatively quick and easy to undertake.
- relatively cheap to undertake.
- only method useful in rare disease.
- can be used to study the effect of many exposure variables on a single disease outcome.
Drawbacks of case control studies
- prone to selection and record bias
-can't measure relative risk or provide incidence estimates.
- cannot be used for rare exposure.
6. Cohort study - cohort studies are forward looking that is they look for the development of disease in a group of individuals (the cohort) free of the same at the beginning. The group is followed up over a period of time. During this period some person's will develope the disease under the study while others will remain free of disease. the characteristics are compared between those who suffered from disease and those who remained free from disease.
7. Randomised controlled trial - (RCT) A study in which people are allocated at random (by chance alone) to receive one of several clinical interventions. One of these interventions is the standard of comparison or control. The control may be a standard practice, a placebo ("sugar pill"), or no intervention at all. Someone who takes part in a randomized controlled trial (RCT) is called a participant or subject. RCTs seek to measure and compare the outcomes after the participants receive the interventions. Because the outcomes are measured, RCTs are quantitative studies.
In sum, RCTs are quantitative, comparative, controlled experiments in which investigators study two or more interventions in a series of individuals who receive them in random order. The RCT is one of the simplest and most powerful tools in clinical research.
8. Community trial - A community trial is the modification of the clinical trial where instead of individuals being allocated to experimental control groups whole communities are randomly allocated to receive a specific interventions and analysis is done for whole community rather than for individuals in the communities.
9. Vaccine trial - when a randomised controlled trial is done to test efficacy of a vaccine in preventing disease is called a vaccine trial.
10. Descriptive epidemiology - Descriptive epidemiology aims to describe the distributions of diseases and determinants. It provides a way of organizing and analyzing these data to describe the variations in disease frequency among populations by geographical areas and over time (i.e., person, place, and time).
11. Analytic epidemiology - Analytic epidemiological studies aim to investigate and identify factors associated with the presence of disease within populations, through the investigation of factors which may vary between individual members of these populations.Conceptually, this involves investigating the disease experience amongst different 'groups' of animals within an overall population, distinguished according to the factor(s) of interest. These factors can be classified as one of the components of the 'epidemiological triad' of Host, Agent and Environment, many of which are closely interrelated with each other.
12. Sampling - sampling can be defined as a process of selecting a statically determine number of subjects from the universe or reference population which provides an accurate estimate of the problems being studied. In this only a proportion of the reference population is covered but the results approximate the actual prevalence of the disease condition in the reference population.
a sample is the minimum number of people ard units you need to be contacted or examined to obtain statically acceptable results and their by permits valid inferences to be drawn.
13. Different sampling methods
- simple random sampling
-systematic random sampling
- stratified random sampling
- cluster sampling
- multistage sampling
14. Epidemic - An epidemic is the rapid spread of infectious disease to a large number of people in a given population within a short period of time, usually two weeks or less. in an area where a disease has not been seen for many years even the occurrence of a single case may be sufficient to call it an epidemic.
Some recent epidemics in India
-epidemics of dengue Japanese and cystitis are reported from time to time.
-recent outbreak of plague in India where cases were not seen for many years is an example of an epidemic.
Important note - epidemic disease need not necessarily be communicable disease hence smoking can also be seen as an epidemic.
15. Pandemic - an epidemic which breaks out across many continent is called pandemic.
Some examples of pandemic disease -
- HIV AIDS and smoking is also an example of pandemic as they have affected millions of people across the world.
- drug resistant tuberculosis is also an example of pandemic.
16. Endemic disease - the constant continuous or usual presence of a disease in a defined Geographic area or delimited territory is called an endemic disease.
an endemic disease may become an epidemic if the number of cases usually seen suddenly increase in population.
17. Prevalence rate - Prevalence, sometimes referred to as prevalence rate, is the proportion of persons in a population who have a particular disease or attribute at a specified point in time or over a specified period of time. Prevalence differs from incidence in that prevalence includes all cases, both new and preexisting, in the population at the specified time, whereas incidence is limited to new cases only.
18. Point prevalence refers to the prevalence measured at a particular point in time. It is the proportion of persons with a particular disease or attribute on a particular date.
19. Period prevalence refers to prevalence measured over an interval of time. It is the proportion of persons with a particular disease or attribute at any time during the interval.
20. Incidence rate - incidence rate refers to the number of new cases occurring in a population over a specific period of time. When the denominator is the sum of the person-time of the at risk population, it is also known as the incidence density rate or person-time incidence rate.
21. Relationship between prevalence and incidence -
Prevalence = (Incidence Rate) x (Average Duration of Disease).
22. What increases prevalence of disease
Following factors can cause the increase ini prevalence of disease -
- the duration of the disease is very long that is chronic conditions.
- the level of incidence that is the higher the incidence the larger is prevalence.
- increased method of diagnosis that leads to detection of large number of cases than before.
- availability of effective treatment which prolongs life such that individual lives longer while still suffering from disease.
- sudden Migration of cases into an area where the disease was not common earlier.
23. What decreases president of a disease ?
- a very short duration of the disease.
- a very low incidence of disease.
- lack of proper Diagnostic equipment or skills for the detection of disease.
- disease with the high mortality such that very few individuals survive.
24. Primary case - the first case of a disease which occurs in a community / area is called the primary case. many times the primary case may not be recognised as the disease comes to notice much later.
25. Co primaries - in some disease like acute conjunctivitis a number of primary cases may occur almost at the same point in a time. In such a scenario the primary cases are referred to as co primaries.
26. Index case - the first case which comes to the attention of the healthy authorities in an area is referred to as index case. Such a case maybe or may not be the primary case.
27. Secondary attack rate - The secondary attack rate is defined as the probability that infection occurs among susceptible persons within a reasonable incubation period following known contact with an infectious person or an infectious source.
28. Secular Trend - the pattern or trend of the disease frequency changes only over many years then it is called a secular Trend.
29. Cyclic Trend - if the occurrence of disease changes over a short duration of time like in a year it is called a cyclic Trend.
Most epidemic diseases in India shows the cyclic trend .
30. Seasonal changes - some disease change in frequency over seasons and such changes are referred to as seasonal changes. Examples of seasonal changes are measles and chickenpox.
31. Herd immunity - Herd immunity (also called herd effect, community immunity, population immunity, or social immunity) is a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, thereby providing a measure of protection for individuals who are not immune.
Herd immunity only works if most people in the population are vaccinated (for example, 19 out of every 20 people need to be vaccinated against measles to protect people who are not vaccinated). If people are not vaccinated, herd immunity is not guaranteed to protect them.
32. Nosocomial infection - A hospital-acquired infection (HAI), also known as a nosocomial infection, is an infection that is acquired in a hospital or other health care facility. Usually such infections or more difficult to manage as they are generally resistance to most of the common antibiotics.
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