Disease transmission

1
Disease transmission

• In a nursing context one of the major aims is to
  prevent infection.
• So for every episode of infection
• 1) Where did the organism come from?
• 2) How did it get there?

2
Reservoirs of Infection

• A reservoir is the original source of the
  organism, not necessarily the most recent.
• Where the organism normally lives and multiplies.
• Reservoirs for Human Disease
• Humans animals environment

3
Human reservoirs

• endogenous versus exogenous

Infected people
symptomatic
true
asymptomatic
Convalescent phase
carriers
Incubation period
Normal flora
Infect somebody else
Infect yourself (endogenous)
4
Endogenous infection

• What conditions can produce an endogenous
  infection?
• Change in host defenses / physiology.
• Change in site of the organism.
• Change in number of the organism.

5
More reservoirs of infection
Animals
Normal flora
infected
Different disease
Same disease
Environment
Especially the soil, but also water.
6
Portals of exit and entry

• Where the organism LEAVES one host and ENTERS
  another.
• - usually identical in both hosts.
• - can be different.
• - some organism have multiple portals.
• Portal of entry can modify disease.
• Portal of entry can also modify communicability

7
Direct and Indirect Transmission

• Direct transmission
• Indirect transmission

Reservoir
New host
New host
intermediate
Reservoir
Vector (living)
Vehicle (non living)
Food, water, fomites
biological
mechanical
8
Shigella
faeces
flies
fingers
food
New host
Hepatitis B
Body fluids
semen
needle
Blood donation
New host
9
Transmission through air

• Droplet nuclei - about 1m - DIRECT.
• Airborne - more than 1m
• - longer time span
• - air now becomes a vehicle.
• - INDIRECT

10
Bloodborne infections

• Relatively non communicable due to portal of
  entry and exit.
• HIV, Hep B and C, arboviruses.
• Mechanisms of transmission
• Blood transfusion, IV inoc
• Insects
• Cutaneous inoculation (needlestick)

11
Common source outbreaks

• Same infection in many people acquired via common
  exposure.
• Compare with a propogated outbreak.
• Food and water are often implicated as common
  source vehicles.

12
Diseases in a population

• Sporadic, endemic or epidemic
• Morbidity, mortality, prevalence, incidence
• Level of infection is governed by
• Infectivity of organism (dose required)
• Level of exposure (means of transmission)
• Susceptibility of the population.