Definition and Concept of Epidemics, Endemic, Sporadic and Pandemic, Screening

Definition and Concept of Epidemics, Endemic, Sporadic and Pandemic

Endemic

The habitual presence of a disease within a given geographic area is called endemic. It is also termed as to describe levels of infection which do not exhibit wide fluctuations through time in a defined place. Stable endemicity is where the incidence of infection or disease shows no secular trend for increase or decrease. For example, respiratory infections are endemic in the world, malaria is endemic in the southern hemisphere, visceral leishmaniasis is endemic in Nepal and India, lyme disease is endemic in US. Due to frequent travel of the people, every infectious disease can become endemic globally.

Hyperendemic : It expresses that disease is constantly present at a high incidence or prevalence rate and affects all age group equally.

Halo endemic: It is a high level of infection beginning early in life and affecting most of the child population leading to a state of equilibrium such that the adult population shows evidence of the disease much less commonly than do the children as in the case of malaria.

Sporadic

The word “sporadic” means “scattered around”. The scattered distribution of the disease in low frequency of occurrence is called sporadic. The cases occur irregularly, haphazardly from time to time and generally infrequently. The cases are so few and separated widely in space and time that they show little or no connection with neither each other nor a recognizable common source of infection. For example: Tetanus.

Pandemic

The global distribution of the disease affecting all population is called apandemic. It is an epidemic that encompasses the entire world. For example, AIDS is a pandemic; the bird flu is often pandemic. In the past several pandemics have been reported and in the future, there are possibilities of increasing pandemics because of acombination of worldwide rapid travel and the increasing human populations.

Concentrated epidemic

An epidemic affecting a particular group of population is called aconcentrated epidemic. HIV/AIDS in Nepal is said to be concentrated epidemic since it is focused on specific group e.g. commercial sex workers, migrant population, and intravenous drug users.

Epidemics

An epidemic is an occurrence, in a community or region, of a group pf illness of similar nature, clearly in excess of normal expectancy. A relatively sudden increase in the number of cases of a particular disease in a particular area or place refers epidemics. For example, a local epidemics of the measles, dengue, cholera epidemic in India etc. The area and the number of increased cases are always part of the description of any epidemic. The concept of an epidemic, today, is not limited to communicable disease. Lung cancer, traffic accidents and adverse effects of some medications such as thalidomide, are the examples of disease due to non-communicable agents.

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Fig. Disease endemic and epidemic curve

Screening

Definition

The process, by which an unrecognizable disease or defects are identified by test that can be applied rapidly on a large scale is known as screening. Screening sorts out healthy people from those whom may have a disease.

it is not diagnostic. The presumptive identification of unrecognozable disease or defects by the application of tests, examinations, or other procedures, which can be applied rapidly (United States Commission on Chronic Illness, 1957) is known as screening. Screening is a medical investigation which does not arise from a patient's request for advice for a specific complaint (McKeown, 1968).

There are different types of screening:

Mass screening: It involves the screening if a whole population

Multiple or multiphase screening: It involves the use of a variety of screening tests on the same occasion.

Targeted screening: It involves screening of specific groups.

Case finding or opportunistic screening: It is restricted to patiebts who consult a health practitioner for some other purpose.

Basic Feature of Screening Program

The following are the basic features for the institution of the screening program.

Recommending Screening Procedures

Screening procedure is recommended to find the following:

• the current burden of morbidity, mortality and suffering caused by the condition
• the validity and acceptability of the screening procedure
• the effcetiveness of the resulting intervention

Burden can be considered in two broad are:

1. The impact on the individual in term of potential years of life lost, the extent of the disability, pain and discomfort, cost of treatment, and the impact on the individual's family.
2. The impact on society-mortality, morbidity.

Criteria for Assessing the Screening Test

Simplicity:a test should be simple to perform, and easy to interpret.

Acceptability:since participation in screening is voluntary, atest should be acceptable to those undergoing it.

Accuracy:a test must give true measurement of the condition or symptom under investigation.

Cost:the expense of test must be considered in relation to the benefits of detection of disease.

Precision or repeatability:the test should give consistent results in repeated examinations.

Sensitivity:a test should be capable of giving positive findings when the person being screened has the disease being sought.

Specificity:a test should be capable of giving negative findings when a person being screened does not have the disease being sought.

Criteria for Instituting a Screening Program

The following are the criteria for instituting a screening program:

Disease

• Serious
• High prevalence of preclinical stage
• Natural history understood
• Long period between first signs and overt disease

Diagnostics tests

• Sensitive and specific
• Simple and cheap
• Safe abd acceptable
• Reliable

Diagnosis abd treatment

• Facilities are adequate
• Effective, acceptable and safe treatment available

Finally, these screening tests must be:

• Cheap and easy to apply
• Acceptable to the public
• Reliable and valid

Biases in Screening

1. Lead tine bias-It is the interval between the diagnosis of a disease at screening and when it would have been detected due to the appearance of symptoms. For example, screening ofincubation period of disease.
2. Length bias-This happenss when the disease is a heterogenous with respect to its natural history. For example, several diseases at the same time.
3. Self selection bias-People who choose to participate int he screening program are different from the ones who refuse.

References

Atlas, RM and R Bartha. Microbial Ecology:Fundamentals and Applications. The Benjamin Cummins Publication co. Inc., 1998.

Gordis, L. Epidemiology. third edition. 2004.

Maier, RM, IL Pepper, and CP Gerba. Environmental Microbiology. Academic press Elsevier Publication, 2006.

Park, K. Park's Text Book of social and prevention Medicine. 18th edition. 2008.