What are the two ways an infection can spread?
From a non-human source to humans.
From person to person (through either indirect or direct contact).
What are some examples of non-human sources?
Food/water: salmonella (food-poisoning)
What are some examples of person to person infections?
What is an example of "indirect" transmission from person to person?
This happens via vectors.
Example of tansmision via vectors: mosquitos tramission of malaria.
What are the consequences of transmission?
- Endemic disease
What is an endemic disease?
A disease with an incidence of the normal range.
Example: chicken pox in children
What is an outbreak of a disease?
Two or more cases linked in time and place.
What is a disease epidemic?
A rate of infection that is greater than the usual background rate.
What is a disease pandemic?
A very high rate of infection spreading across many regions, countries, and continents.
What are some reasons for a disease outbreak?
- New pathogen
- New hosts
- New practice
What factors could a new pathogen have that would result in an outbreak?
- Virulence factors
- Antibacterial resistance
What reasons could new hosts have to cause an outbreak?
- Non-immunes (never encountered pathogen before)
- Healthcare effects (comorbidities)
What reasons could new practice have to cause an outbreak?
What is the main factor that determine transmissibility?
The infectious dose
What is the infectious dose?
The number of micro-organisms required to cause infection.
How can the infectious dose vary?
Can vary by the following:
- presentation of the micro-organism
- immunity of potential host
How does infectious dose affect the tranmissibility of a disease?
The larger the infectious dose, the more difficult it is to be affected by the pathogen.
What can we act on to prevent the spread of infections?
- Pathogen (including the vector)
What actions can be taken against pathogens to prevent infections?
Reduce/ eradicate pathogens:
- antibacterials (including disinfectants)
Reduce/ eradicate vectors:
- eliminate vector breeding sites
What actions can be taken on patients to prevent infections?
- medical treatment
- passive (e.g. maternal antibody, IV immunoglobulin)
- active (e.g. vaccination)
What is 'herd ammunity'?
The concept of majority people being vaccinated, and therefore unable to contribute the spread of an infection.
This by proxy, protects those who aren't vaccinated.
What actions can be taken on practices to prevent infections?
Avoidance of a pathogen or its vector
- geographic ("don't go there")
- protective clothing, equipment
- safe sex
- safe disposal of sharps
- food and drink preparation
What actions can be taken on a place to prevent infections?
- safe water
- safe air
- good quality housing
- well designed healthcare facilities
What are some of the consequences of good infection prevention?
- Decreased incidence or elimination of a disease/ organism
Examples: smallpox, polio
What are some consequences of bad infection prevention?
- Decreased exposure to pathogen leads to decreased immune stimulus. This increases susceptibility and can lead to a potential outbreak.
- Later average age of exposure leading to more severe infection
- Examples: polio, chicken pox
- Examples: polio, chicken pox