Public Health Flashcards
What is the chain of infection? Why does it help to understand it?
Understanding the chain of infection allows appropriate control measures to be introduced/recommended.
Infectious agent–>reservoir–>portal of exit–>modes of transmission–>portal of entry–>susceptible host.
Reservoir - human, animal, plant, soil where the gent normally lives and multiplies. Not necessarily the source or vehicle of infection. This may include colonisation, where the agent multiplies in/on host without causing infection. Infectious diseases transmissible from animal reservoirs to humans are called zoonoses.
Portal of exit: path by which the agent leaves the reservoir/host usually corresponds with the site at which infection/the agent is localised.
Modes of transmission: direct, indirect and airborne spread
Portal of entry - the path by which the agent enters the susceptible host
Susceptible host - person capable of becoming infected
What are the modes of disease transmission?
Direct transmission
- direct route: contact with skin, blood, other fluids
- respiratory route - droplet spread: sneezing, coughing, talking
- faeco-oral route: faecal material transferred directly to mouth
Indirect transmission
- vehicle-borne route: via contamined inanimate objects e.g. touch points
- vector-borne: either mechanical e.g. simple carriage by a flying insect from A to B or biological: some form of multiplication or development of the agents before transmission is possible
Airborne spread
Dissemination of fine microbial aerosols which remain suspended in the air for some time
What is an epidemiological framework?
Model of infectious disease causation ‘epidemiological triangle’ - interaction between the 3: host, agent and environment.
Host - consider susceptibility, likelihood of exposure, and response to agent. Includes: age, sex, nutrition, ethnicity, culture, lifestyle factors etc
Agent: organism, infectivity, pathogenicity, virulence, reservoir
Environment: extrinsic factors that affect the agent and the opportunity for exposure e.g. climate, sanitation etc
What does infectivity mean?
the likelihood that a person will become infected following exposure.
What does pathogenicity mean?
the likelihood that an infected person will suffer clinical disease
What does virulence mean?
the likelihood the infected person will become severely ill or die
What does incubation period mean?
time between acquiring infection and onset of symptoms
What does latent period mean?
time between acquiring infection and becoming capable of transmitting infection to others
What does period of communicability mean?
time during which an infected person is capable of transmitting the infection
