tutorial 1b Flashcards
hill’s criteria for causation
strength consistency specificity temporality biological gradient plausibility coherance experiment analogy
strength
a smaller association does not mean that there is not a casual effect through the larger the association, the more likely that is casual
specificity
causation is likely if there is a very specific population at a specific site and disease with no other likely explanation. The more specific an association between a factor and an effect is, the bigger the probability of a casual relationship
temporality
the effect has to occur after the cause ( and if there is an expected delay between the cause and effect, then he effect must occur after that delay)
biological gradient
greater exporsure should generally lead to greater incidence of the effect. However, in some cases, the mere presence of the factor can trigger the effect. other cases, an inverse proportion is observed: greater exposure leads to lower evidence
plausibilty
a plausible mechanism between cause and effect is useful
coherence
coherence between epidionilogical and laboratory findings increases the likelihood of an effect
experiment
occasionally it is possible to appeal to experimental evidence
analogy
the effect of similar factors may be considered
what is an outbreak
an unusaul, statistically significant increase in the incidence of a particular disease
Usually occurs during a brief interval
Caused by a single microbial strain
why investigate an outbreak
To control further transmission
Todescribe causative agents, host or environment
Toassess prevention interventions
To determine quality of surveillance
In a health setting, exitance of an outbreak should be considered when
A clusterof similar infections occur on one unit or among similar patients
AA cluster of infections associated with invasive devices to occue
HCWs and patients develop the same type of infection
A cluster of infections with organisms typically associated with HAI(resistant organsim)
Goals of an outbreak investigation
Identify contributing factrs
Implement interventions that will prevent additional cases from occuring
Institute measures to prevent future similar outbreaks
Keys questions to address
who is involve? when did it happen? where is it happening? what are the agents? how are the agents being transmitted?
investigation inspectations
an investigations ma show association but be unable to prove causation
do not expect to find that every case patient is exposed to the factor that is implicated as the cause
confirm existance of outbreak
background rate of infections vs outbreak perion rate of infection
identy and cout cases - crate a case definition (based on the know facts of the outbreak)
date of onset illness
sign and symptoms
laboratory or diagnostic findings
presence in a specific ward or location
arrange the data in terms of time, place and person
time- provides valuable epidimiolgic inferomation
place- geographic clustering
person- underlying host characteristics that predispose to infection, ag, see, nutritional status, underlying diseases, immunisation history, immunosuppressive therapy
evaluation of control measures
has the incidence of new cases decreased or ceased
conitnua to monitor to avoid misinterpretation of a temporary reduction
control measures successful if acceptable rate of infection is maintained
communicate findings
provide regaular updates to team and personnel in effected areas
also patients, relatives, - ward of media, telephone tachniques
