Epidemiology is the study of patterns of disease occurrence
in populations, and the factors that affect them.
Epidemiology of HIV is The study of how HIV moves
between individuals, and its effects on populations.
Allows you to consider very large data sets to generate
statistically meaningful data.
Epidemiological studies give information about
populations, not about specific individuals.
Benefits of epidemiology
Identify new diseases
Identify populations at risk for a disease
Identify possible causative agents
Identify factors or behaviors that determine the risk for a disease, and also determine the relative importance of that factor in causing the disease
Rule out factors or behaviors as causes
Evaluate therapies
Guide the development of effective public health measures and preventative strategies
Types of epidemiological studies
1. Descriptive studies – gathers data from existing
or previous epidemics
2. Analytical studies – builds upon quantitative data
from existing or previous epidemics
Types of Descriptive studies
Descriptive studies – gathers data from existing
or previous epidemics
Look for clustering by person, place, time,
or a combination.
Case Reports/Case Report Series
Cross-sectional/Prevalence Studies
Types of Analytical studies
Analytical studies – quantitative data from existing
or previous epidemics
Experimental/Interventional Studies
Observational Studies
Analytical studies – quantitative data from existing
or previous epidemics
Correlations – studies may show different outcomes.
Possibilities:
There is no causal relationship
There is an indirect relationship
There is a direct causal relationship
What type of associations are needed to show a casual relationship?
Types of Analytical studies
Criteria for a causal relationship:
Strength of the association between the factor and
the disease. The strongest collation would be if everyone who with the factor gets the disease, and no one without the factor does. Perfect correlation is rarely achieved.
The association is consistent. The same correlation is observed in other studies under different circumstances.
The association has the correct time relationship. Exposure to the agent must occur before the onset of the disease.
The association has a biological plausibility. The association of the factor with the disease must make biological sense.
Types of Analytical studies
The following slides show examples of the type of information that can be obtained
from analytical studies using
epidemiological data
New AIDS conversions in the US by year: 1978-2010
AIDS Distribution by
Risk Group
AIDS Distribution by Ethnicity
Relative Risk of Unprotected Anal Sex
AIDS Cases by Risk Group
has changed over time
AIDS Cases by Ethnicity
has changed over time
Worldwide distribution of HIV Infection 2008-2009