PUBH 3131 Lecture Notes - Lecture 11: The New England Journal Of Medicine, Chikungunya, Infection
Studying epidemics was long seen as the primary function of an epidemiologist…because
stopping epidemics has to be done at the population level and was the real motivator to the
very idea of PUBLIC health. You can see why when you look at history…
Consider this example
Turns out it’s pretty tricky to find the excess mortality due to the 1918 pandemic. These
numbers are only for France – but consider that the underlying mortality was during WWI.
Epidemics
Endemic vs. epidemic vs. Pandemic
(if you don’t remember these go back to past slides ☺)
Outbreaks
Hopefully you remember this - technically it is the same as an epidemic but tends to be the
term of choice for local and brief outbreaks
Always communicable?
Not necessarily – think opioid addictions or obesity. Generally “outbreaks” are due to some
biological agent but in the case of foodborne outbreaks they may NOT be communicable (for
example botulism)
Reviewish: Communicable Disease Transmission
Direct transmission
Indirect transmission
Vehicle transmission (inanimate)
Vector transmission (animate)
aka vector borne
Airborne
Either!
What’s a fomite?
Ref: Jones DS et al. N Engl J Med 2012;366:2333-2338.
Impact of Infectious Diseases on Human Health
Emerging Infectious diseases
Category used to identify new or re-emerging infections according to CDC
Inclusion on list helps to prioritize research needs
Depends on surveillance to be identified as emerging
Often abbreviated as EID
Factors Influencing (Re)emerging ID*:
Population growth
Changing living patterns and geographic alterations
War and social disruption
Climate change
Changes in underlying health of a community
Travel
Medical advances
Poor vaccine coverage
Countries and territories where chikungunya cases have been reported* (as of March 10,
2015)
*Does not include countries or territories where only imported cases have been documented.
This map is updated weekly if there are new countries or territories that report local
chikungunya virus transmission.
find more resources at oneclass.com
find more resources at oneclass.com
Pathways of Infection
Pathways “take homes”
Routes of entry and exit disease specific
Important to know for control
May be simple safe guards: i.e. handwashing!
Essential Terms
Infectivity: ability of agent to invade and multiply in host
Pathogenicity: ability of agent to produce clinically apparent illness in host
Virulence: ability of agent to produce severe disease in a host
Immunogenicity: degree to which an agent provokes an immune response in host
Measures of communicable disease
Attack rate(%)= (cases / exposed*) X 100
this can be a measure of infectivity
looks easy…but the cases must be found and
who will we count as exposed??
During an epidemic investigation the entire local (to the investigation) population is generally
considered exposed…at least initially
i.e. # new cases in defined population/ # at risk in defined population
→This will be same as population incidence … so it may not be a completely accurate
measure of infectivity
In an outbreak where the source of exposure is known (say a community potluck) or where
those who might be exposed are clearly limited (say a cruise ship, or a prison) the attack rate
will be a better measure of infectivity since it can be limited to those (probably) exposed.
NOTE: attack rates can be used in describing outbreaks even when the cause is not
communicable (like that sad potluck again).
Measures of communicable disease
To get a better idea of disease transmission a contact study may be conducted and an attack
rate is calculated using only those (secondary cases) who acquire the disease after contact
with a primary case. Then the number exposed is based on all susceptible individuals the
primary case had contact with. This special form of an attack rate is known as the
→ Secondary Attack Rate
→ Only applies if disease is spread person to person
But wait – is the number of cases really the number infected?!?
Measures of communicable disease
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Studying epidemics was long seen as the primary function of an epidemiologist because stopping epidemics has to be done at the population level and was the real motivator to the very idea of public health. You can see why when you look at history . Turns out it"s pretty tricky to find the excess mortality due to the 1918 pandemic. These numbers are only for france but consider that the underlying mortality was during wwi. Endemic vs. epidemic vs. pandemic (if you don"t remember these go back to past slides ) Hopefully you remember this - technically it is the same as an epidemic but tends to be the term of choice for local and brief outbreaks. Not necessarily think opioid addictions or obesity. Generally outbreaks are due to some biological agent but in the case of foodborne outbreaks they may not be communicable (for example botulism) Category used to identify new or re-emerging infections according to cdc.
