Basic Infectious Disease Epidemiology

1. Basic Infectious Disease Epidemiology

3. Spread of infection Three conditions must be met for infection to spread from person to person If any of these conditions are not met, the chain is broken and the infectious disease does not spread.

4. 3 conditions required for infection to spread from one person to another 1. One person must be infected with a microorganism 2. The other person must be susceptible to infection with that microorganism 3. The microorganism must be able to leave the body of the infected person and enter the body of the susceptible person.

5. Susceptibility Ability to become infected with an organism when exposed to it People may loose susceptibility (or become immune) once they have been: infected with the organism vaccinated Medications may reduce susceptibility temporarily

6. Mode of transmission The way a microorganism is spread from an infected person to a susceptible person

7. Modes of Transmission

8. Direct transmission The spread of an organism from one person to another as a result of the direct contact of an infected and a susceptible person The modes of direct transmission direct contact droplet spread

9. Direct contact The organism is passed to a susceptible person when he or she has contact with an infected person’s skin, mucus membranes or body fluid (blood, urine, feces).

10. Droplet spread The organism is spread to a susceptible person in respiratory secretions that form when an infected person breaths, coughs or sneezes. A susceptible person can become infected if the droplet enters his eyes, nose or mouth directly or via contamination of hands.

11. Droplet Spread Considered direct transmission because droplets are heavy so they do not tend to travel more than 6 feet from the infected person A susceptible person who is not near an infected person will not become infected The spread of disease by respiratory droplets usually requires extended contact

12. Indirect transmission Occurs when an organism is spread from an infected person to a susceptible person via an intermediary or go-between. Via the air = airborne Via an insect = vectorborne Via an inanimate object = vehicleborne

13. Types of infection Colonization – infection present on surface of body – Organism propagating at a rate sufficient to maintain its numbers without producing identifiable evidence of any reaction in host Inapparent or subclinical infection organism not only multiplying but also causes a measurable reaction that is however not clinically detectable Symptomatic infection Organism causes clinically detectable reaction

14. Time parameters of interaction Latency Period = the time between infection agent and onset of infectiousness Incubation Period = the time between infection and onset of symptoms Latency period may not be the same as the incubation period A disease may have incubated but remains latent, or dormant, within the body. For instance, the latent period between exposure to HIV (human immunodeficiency virus) infection and the onset of AIDS (acquired immunodeficiency syndrome) may be many years Example Influenza – incubation period is longer than the latency periodA disease may have incubated but remains latent, or dormant, within the body. For instance, the latent period between exposure to HIV (human immunodeficiency virus) infection and the onset of AIDS (acquired immunodeficiency syndrome) may be many years Example Influenza – incubation period is longer than the latency period

15. Time parameters of interaction