Principles of Infectious Disease Flashcards
EPidemiology
The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to control health problems.
What is an infectious disease?
An illness
due to a specific infectious agent or its toxic products
that arises through transmission of that agent or its products
from an infected person, animal, or reservoir to a susceptible host,
either directly or indirectly through an intermediate plant or host, vector, or the inanimate environment”
Difference about infectious disease.
The organisms that cause infectious diseases are necessary causes
Certain organisms may cause infection and there may be no evidence of disease for years although the individual may spread the infection
Immunity may be acquired by exposure to certain organism or through immunization with vaccines and this may provide protection against re-infection with the same organism
Source: Human to human, Zoonosis.
One can sometimes immediately control predisposing factors but often not
Difference between infection and disease.
Infection
Invasion of a host by an agent, with subsequent establishment & multiplication of agent
May or may not lead to disease
Disease
A condition of abnormal physiological functioning/ anatomical structure
Sometimes the host response contributes more to tissue destruction/malfunction than the infectious agent
Compare source to reservoir.
Source:
The actual object, animal or person from which the infection is acquired (Giesecke)
E.g. airvents, water tank
Reservoir:
The natural habitat of the infectious agent
Humans are reservoirs for which organisms?
Syphilis, Gonorrhoea, HIV, Hepatitis
Animals are reservoirs for which organisms?
Rabies, Brucellosis
soil are reservoirs for which organisms?
Histoplasma, tetanus
Water are reservoirs for which organisms?
Legionella, Pseudomonas
Give Examples of direct transmissions.
Mucous membranes-STD
Placental-Taxoplasmosis
Blood-Hep B
Skin- Herpes 1
Sneezes, cough- Influenza and TB
Indirect transmission
common vector/vehicle
Food-borne
E.g. salmonella (typhoid)
Water
E.g. Cholera, Hepatitis A
Objects
E.g. scarlet fever (toys in in a nursery)
Vectors (mosquitoes)
E.g. malaria
When is prevalence important for Infectious diseases?
Challenges with prevalence:
Some infectious diseases have short duration/occurs repeatedly
Many infectious diseases have a short duration and may occur repeatedly, and thus prevalence is not as important a measure in these instances
E.g. Diarrhoeal/resp infections (point prevalence may be low but annual incidence high)
When is prevalence useful:
Some infectious diseases are chronic in nature
Some infectious agents have a chronic nature, and both incidence and prevalence are important measures with prevalence providing a more accurate measure of risk of infection and the size of the infectious pool
Why is it important to understand time periods of infection?
To monitor and investigate outbreaks
To know how fast the infection/disease will spread/decrease
Incubation period
The time between exposure to an infectious agent and the onset of symptoms or signs of infection
Serial interval
For diseases that are spread from person to person the time period between successive generations
Time between the appearance of similar SYMPTOMS in successive generations
If person is infectious before symptoms occur (i.e. latent period shorter than incubation period) the serial interval will be shorter than the incubation period
