principals of infectious diseases Flashcards
What are the levels of infection
Colonistation
subclinical infection
latent infection
clinical infection
What is a communicable disease
Capable of being directly or indirectly transmitte from n infecte person to another, or from animal to human or from environment to human
What are the three points in an epidemiological triad of disease transmission
Host
agent
environment
What are the different modes of transmission
Direct- contact HIV/STI’s
Contact with soil -helminths
inoculation into skin/mucosa -schitosomiasis
Transplacental- syphilis rubella
Indirect vehicle-borne - food water (salmonella, shigella, chlorea) Vector borne- malaria, dengue Airborn-measels fomite born- scabies Unclean hands and fingers Droplet infection TB
What is the iceberg concept of infection
Clinical perception is only of those who have reached the symptomatic period but there may be many more subclinically in
How is the rate of transmission measured
Basic reproductive number
the mean number of individuals directly infected by an infectious case throughout the total infectious period, when introduced to a susceptible pop
What is the equation for R0
P=probability of transmission per contact
C= contacts per unit time
D= duration of infectiousness
PxCxD
What is R>1
The infection will become epidemic
What if R=1
The infection will become endmeic
Define endemic
Persistent occurance/prevalence with low to moderate levels at all time (STI)
Define epidemic
sudden occurance clearly in excess of expected for a given pop at a given time
Explain herd immunity
form of immunity that occurs when the vaccination of a significant portion of a pop provides a measure of protection for individuals who have not developed immunity
How can R0 be used to with herd immunity
helps calculate the lowest percentage of people need to be immune to prevent epidmeics
the higher the R0 value the higher proportion needed to be immunized
When is a disease outbreak labeled as an epidemic
Sharp rise in cases of an endemic disease (malaria)
just one confirmed case of a non-endemic disease (cholera)
1 suspected case of a highly fatal case (ebola)
5 or more suspected cases or at least 3 confrimed cases of measels
Define eradication and suggest a disease to which this is applicable
Eradication it the termination of all transmission of the infectious agent through survellance and containment, none in the world= small pox
Define elimination and an example of a disease that has been eliminated
Eradication from a large geographic region. Polio measels and diptheria, tetanus, whooping cough, yellow fever
Define hyper endemic
equally endemic in all age groups
Define holoendemic
children more than adults
define a pandemic
widespread epidemic distribute or occuring throughout a region/country/continent/glabally
Define point source outbreak
Point source- same exposure over a limited define period of time, usually within one incubation period, rapid rise, peak and then gradual fall
Definecommon persistent source outbreak
exposure to source prolonged and may occur over more than 1 incubation period eg malaria
Define common intermittent source outbreak
sporadic cases of any disease
Define propagated progressive source outbreak
case of disease serves as sources for later cases, series of sucessively larger peaks,reflective of increasing numbers of cases caused by person to person contact
An outbreak has been confirmed what are the two routes of action
Immediate control measure
further investigations
Describe what immediate control measures are there in an outbreak
Prophylaxis
Exclusion/isolation
public warning
hygiene measures
Describe what further investigations can be done when an outbreak has been identified
aetiological agent mode fo transmission vehical of tranmission source of contamination population at risk exposure causing illness
When the cause is know but the mode of tranmission isnt what is prioity
investigation
When the cause is unknown but the source is known what is prioity
Both investigation and control equally important
If the causative agent is unknown and so is the source of the transmission what is the priority
investigation
What are the 10 steps n outbreak investigation
1prepare for field work
2confirm if it is an outbreak
3verify diagnosis and confirm disease
4define an identify case
5descriptive;orient data in terms of time place and person
6Interpret and develop hypothesis
7Analyse; evaluate hypotheses
8draw conclusions
9implement control and prevention measures
10communicate findings and write a report
How do you identify cases in a outbreak investigation
based on timing and infection: index=1st case primary=case that brings infection into a pop secondary=infected my primary case based on degree of certainty: possible/suspected, few features probable- typical features no lab confirmation confirmed
What is the development of a line listing
Identifying info demographic info clinical info risk factor info reported info
What is the role of the lab
confirm diagnosis identify new pathogens tracing spread through typing pathogen antimicrobila susceptabilty as a guide to treatment post-outbreak survellience
How can the source, mode or vehicle of transmission be identified
geographical scope
How can epidemic curves help us
helps understand size of epidemic relationship to endemics pattern of spread time course and where you are in the course
How can a hypothesis be evaluated
Against facts, or using analytical epidemiology to quantify relationships and explore the role of chance
What is the case fatality rate
the proportion of infected indivduals who die from the infection
deaths/diseased x 100
What is the attack rate
proportion of non-immune exposed individuals who become clinically ill
ill/ill+well x100
What is the incidence risk ratio
Compare the incidence risk of the disease in the exposed and unexposed groups,
incidence risk of a disk exposed/unexposed
What is the odds ratio
Compare the odds of exposure in cases and controls odds of exposure in cases/odds of exposure in controls
How can it be decided when the outbreak is over
Looking at
no.of suspected persons who are exposed to course and become infected
period of time over which suspetible people are exposed to the source
minimum and maximum incubation periods for the disease
What usually indicates the outbreak is over
2 case free incubation periods
Who are the stake holders
Outbreak investigation staff ph personnel government officials healthcare providers media community
What should the purpose of a final report be
communicate ph messages influence policy evaulate performance training tool legal proceedings
