infectious disease Flashcards
infectious disease
an illness due to a specific infectious agent or its toxic products that arises through transmission from an infected person, animal, or reservoir to a susceptible host, either directly or indirectly through an intermediate plant or animal host, vector, or inanimate environment
features that make infectious diseases different from other diseases
- a case may also be a risk factor due to contact
- a case may be a source without being recognized: asymptomatic
- urgency at a population level
- preventive measure
- cause is often known
infectious disease epidemiology characteristics
- deals with 2 or more populations
- a case is a risk factor
- case if often known
- surveillance
what is infectious disease epidemiology used for
- identification of causes of new, emerging infections
- surveillance of infectious diseases
- identification of the source of outbreaks
- studies of routes of transmission and natural history of infections
- identification of new interventions
epidemiologic triad
host
vector
agent
environment
environment
could include geography, quality of ari and of life
agent
determines the degree of infectivity, virulence, survival, antigenic stability, pathogenicity and immunogenicity
modes of transmission
person to person
vector
common vehicle (water, food)
mechanical vectors (toothbrush, door handles)
subclinical disease
disease that is not clinically apparent and is not destined to be clinically apparent
clinical disease
characterized by signs and symptoms
carrier
an individual who harbours the organism but is not infected: can infect others
dynamic of infectiousness
infection; latent period; infectious period; non-infectious
dynamics of disease
infection; incubation period; symptomatic period; non-diseased
incubation period
the interval between the time of contact and/ or entry of agent and onset of illness: time required for the multiplication of microorganisms
epidemiology of tuberculosis
exposure; subclinical infection; infectious tuberculosis and non-infectious tuberculosis; death
diagnosis criteria for tuberculosis
- tuberculin skin test (TST): low specificity
- interferon-gamma release assay (IGRA): high specificity
latent tuberculosis infection
people with LTBI have tuberculosis in their bodies, but do not have TB disease and cannot spread the infection to other people
agent for HIV
free virus
HIV infection stages
primary infection
clinically asymptomatic stage
symptomatic HIV infection
progression from HIV to AIDS
latent period
time interval from infection to being infectious
infectious period
time during which the host can infect another host
symptomatic period
period in which symptoms of the disease are present
endemic
habitual presence of a disease in a given geographic area
epidemic
the occurrence of a group of illnesses of a similar nature within a given community or region over normal expectancy and derived from a common or a propagated source
pandemic
a worldwide epidemic
herd immunity
resistance of a group to an attack by a disease to which a large proportion of members of the group are immune
virulence
severity of the disease produced by the organism
how is virulence expressed as
number of cases of overt infection/ number of total cases
attack rate
attack rate = number of people at risk who develop disease/ number of people at risk during a specified period of time
individualistic R0
number of infections an infected person would generate throughout their infection if everyone they encountered were susceptible
population R0
the average force for the growth of infection in a population where everyone is susceptible
force of infection
the risk of being infected
equation for R0
R0= p x c x d
p= transmission probability per exposure
c= number of contact per unit time
d= duration of infectious period
