Understand how your patient's condition may be related to the conditions in the community orpopulation within which you practice
Understand how your patient's condition may be related to the conditions in the community orpopulation within which you practice: Excerpt from Avoiding Common Pediatric Errors
Author:
Madan Dharmar, MD
What to Do - Gather Appropriate Data
Disease in an individual is an interaction between the individual (host), the
disease-causing agent, and the environment. Each disease is unique in its
causation and its effect on the individual. For example, the genetic makeup of an individual plays an important role in determining susceptibility
and immunity of the individual when interacting with the disease agent
and the environment. Exposure to a causative agent is a necessary step in
the causation of disease in an individual. Disease could be caused by direct
contact with another individual who has the disease or by contact with a
common vehicle or vector (e.g., contaminated food or mosquito). For an
individual, the risk of exposure to an agent could be related the distribution
ofthediseaseandthecausativeagentincommunityorpopulation.Therefore,
to understand the causation of a disease in a community, frequency of the
disease and their determinants in the community or population need to
be measured. By knowing the conditions in the community, health care
providers can plan to deliver appropriate services. The disease burden in a
community, and the evolution of that disease, helps to estimate the risk of
disease development in the people in the community.
Incidence and prevalence aremeasures thathelp us tobetter understand
the trend and patterns of disease occurrence. The most important step in
determining these measures is to define the disease or what differentiates
the individual as diseased or nondiseased.
Incidence. Incidenceisthemeasureofthefrequencyofnewcasesofadisease
in a population. Incidence is represented as the "number of new cases of a
diseaseoccurringinthepopulationduringaspecifiedperiodoftime"divided
by the "number of persons at risk of developing the disease during the same
period of time."
If the disease is uncommon, for example, incidence can be expressed as
incidence per 1,000 persons by multiplying it by 1,000. For an incidence to
be a measure of risk, a period of time must be specified and all the individuals
in the groups represented in the denominator must have been followed up
for the entire period.
Prevalence. Prevalence is the measure of the frequency of all cases of a
disease in a population. Prevalence is represented as the "number of cases of
a disease present in thepopulation at aspecifictime" divided by the"number
of persons in the population at that specified time." Prevalence can also be
expressed per number population such as per 1,000 population.
There are two types of prevalence: point prevalence, which is the prevalence of a particular disease at one point in time, and period prevalence,
which is the prevalence of a particular disease at any time during a certain
period. For period prevalence, the numerator would include individuals who
had the disease at some point during this time period and they could either
still have the disease, recovered from the disease, or died from the disease.
Here is an example to illustrate the above concepts:
1. InJanuary2001,acommunityof5,000peopleunderwentafreeevaluation
for diabetes mellitus. During this evaluation, 40 people were noted to
have diabetes: 15 were newly diagnosed and 25 were already-known cases
undergoing treatment.
2. The same 5,000 people had a repeat evaluation in January 2003: 30 people
were noted to have diabetes; 10 of them were previously diagnosed with
diabetes by their personal physician in last 12 months. Five of the people
diagnosed in the 2001 screening had died of various causes in 2002.
Point prevalence in January 2001 = (40/5,000) × 1,000
= 8 cases per 1,000 people.
Point prevalence in January 2003 = [(40 - 5 + 30)/(5000 - 5)] × 1000
= 13.01 cases per 1,000 people
Period prevalence (January 2001 to January2003)
= [(40 + 30)/5,000)] × 1,000 = 14 cases per 1,000
Incidence during January 2001 to January 2003
= [(30)/(5000 - 40)] × 1000 = 6.04 cases per 1,000
Relationship Between Prevalence and Incidence. Prevalence of a disease
at a particular time point is dependant on the incidence of the disease and
the duration of the disease. An increase in the incidence of disease results
in an increase of the prevalence of the disease, and a decrease in duration of
disease (cured or died) will result in a decreased prevalence.
Suggested Readings
Altman DG, Bland JM. Diagnostic tests 2: predictive values. BMJ. 1994;309(6947):102.
Gordis L. Epidemiology. 3rd ed. Philadelphia: Saunders; 2004.
Pauker SG, Kassirer JP. The threshold approach to clinical decision making. N Engl J Med.
1980;302(20):1109–1117.
Book Source Details
- Book Title: Avoiding Common Pediatric Errors
- Author(s): Anthony D Slonim MD, DrPH; Lisa Marcucci MD
- Year of Publication: 2008
- Copyright Details: Avoiding Common Pediatric Errors, Copyright © 2008 Lippincott Williams & Wilkins.
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Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Avoiding Common Pediatric Errors
Authors: Anthony D Slonim MD, DrPH; Lisa Marcucci MD
Publisher: Lippincott Williams & Wilkins
Copyright: 2008
ISBN: 0-7817-7489-6
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