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Epidemiology
Epidemiology is the study of the distribution and determinants of health-related states or
events in specified populations and the application of this study to the control of health
problems
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Epidemiology
can; determine which locations or populations to implement disease prevention
programmes, identify sources of infection, and identify unexpected disease patterns
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Incidence is the number of new cases in the population in a defined time
period
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Mortality rate is the proportion of the
whole population who die from a disease in a specific period or area
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Emerging infectious diseases are infectious
that have recently appeared within a population or those whose incidence or geographic
range is rapidly increasing or threatens to increase in the near future
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Re-emerging infectious diseases are emerging
diseases which had been considered to be under control
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Consequences of exposure to infectious diseases
Consequences of exposure to infectious disease include; the organism is unable to survive
due to host immunity, subclinical infection in which an individual is infected but presents with
no or non-specific symptoms, clinical infection in which an individual is infected and displays
obvious symptoms of infection, or becoming a carrier which occurs after an individual has a
clinical or subclinical infection and fails to remove the organism after apparent recovery
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Any
patient who satisfies all the criteria is defined as a case
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Diagnosing a case depends upon the patient displaying symptoms and thus going
to the doctor and upon the doctor ordering the correct tests
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The primary case is the
person who introduced the dishes into a specific population
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Secondary cases are people who become infected through
contact with the primary case
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In the
UK notifiable diseases are reported to; public health Englnd, public health Wales, health
protection scotland, or public health agency Northern Ireland
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Notifiable diseases may differ between countries
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Mathematical models
The attack rate is the probability of contracting the disease
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The attack rate is difficult to measure as it is difficult to accurately determine all the people
who are infected
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Disease incidence; is static if each
case leads to one new case (R=1), increases is each case leads to more than one infective
secondary case (R>1), and decreases if each case leads to less than one infective
secondary case (R<1) which will result in disease control and eradication
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This formula
shows that the basic reproduction number is not specific to an infectious agent only, but also
to a specific host population at a particular point in time
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A completely susceptible population is unusual
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The net reproduction number ®
is the average number of secondary cases in a population where not all individuals are
susceptible
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The lower the proportion of susceptible
individuals in a population, the lower the probability that an infectious individual will be in
contact with a susceptible individual
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The proportion of the
population immune to infection is called herd immunity (HI): HI=1-x
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Susceptible individuals become immune once they
are vaccinated with a highly effective vaccine
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K and B are modifiable factors, K can be altered by changing people's
behaviour, B can be changed by vaccination
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For self-limiting, non-fatal, diseases, can allow natural
immunity to develop with the population
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Hepatitis B virus (HBV) infection is an example of an infectious disease in which
interventions have been implemented to change the basic and net reproduction rate
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Other at risk
populations are also routinely vaccinated
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