General Principles of Infectious Disease Epidemiology and Control Flashcards
Define Epidemiology
The study of the distribution and determinants of health related conditions in populations and how it is applied to the control of health problems
How do we calculate the prevalence of an infectious disease
number of infected/100,00
How do we calculate the incidence of an infectious disease
(# of infected/100,00)/ per annum
Prevalence/per annum
How do we calculate the standard mortality rate due to an infectious disease
(# of deaths/100,00)/per annum
Define R0
This is also known as the reproductive index which signifies the contagiousness or transmissibility of an infective agent.
When R0 < 1 its low
When R0 > 1 it is high
What is viral shedding?
This is the release of a viral illness from an infected person’s body into the environment by sneezing, coughing or speaking
What are the four steps in infection control?
- Data collection and quality
- Description of Infection
- Analysis of Infection
- Predictions and Planning
What are 5 sources of data collection in epidemiology
- Lab reports
- Clinical reports
- Death reports
- Surveillance
- Investigation
Why is the quality of data important and why would data from these sources be inaccurate?
The numbers may not always be accurate. From death certificates for example the death may not be caused by the infection being analyzed, additionally not all deaths come with a postmortem and the cause of death may not be known
Additionally with investigation, not everyone would be comfortable with health officials coming into their homes and conducting a thorough investigation
What are the three categories of description epidemiologists give to infections
- Definite
- Probable
- Possible/Suspected
Suspected infections come about from
no samples, they tend to be secondary infection after being in contact with a confirmed case
Probable infections are determined from
an indeterminate sources, the infection tends to be contracted in the hospital
Definite infections are determined from
A positive sample/source/case
Infections abide by the ‘equation’ below
Index case —–transmission——> Susceptible
The infection can be interrupted at any point.
What three ways can the index case be interrupted?
Prioritizing
- Case definition
- Effective treatment
- Isolation
Infections abide by the ‘equation’ below
Index case —–transmission——> Susceptible
The infection can be interrupted at any point.
What three ways can the transmission be interrupted?
Prioritize
- Understanding transmission routes
- Understanding how to control these transmission routes
Infections abide by the ‘equation’ below
Index case —–transmission——> Susceptible
The infection can be interrupted at any point.
What three ways can the susceptibles be protected
Prioritize
- Isolation
- Immunization
- Chemoprophylaxis
Define chemoprophylaxis
The administration of medication in order to prevent a disease
The most successful infections have the two following traits
- numerous methods of transmission
- persistent pathogens (e.g MRSA and C.difficile are contracted in hospitals where the most intense hygienic practices would be thought to be.)
What is a formite?
An object that spreads a disease
What are the five methods of transmission
- Direct contact
- Formites
- aerosol
- Oral
- Vector borne
Who constructed the first mathematical model to be used in epidemiology?
Bernoullini in 1760
What is the purpose of mathematical models in epidemiology?
These are used in the planning stages of a possible epidemic to determine the probable severity of the infection using R0.
They help
-set priorities for research and determine gaps in knowledge
- evaluate interventions previously used
What are the two main things mathematical models in epidemiology should represent?
- Changes in the infection status of people in the population
- The movement patterns of the infection
What is the aim of the planning stage?
To find a way to achieve R0<1
Explain why infectious diseases are said to be successfully controlled when R0<1
When R0<1 is when there is sufficient herd immunity.
How does R0 affect the herd immunity.
The higher the R0 value the higher percentage pf vaccine coverage is required for herd immunity
e.g The R0 for measles is 12-18 and the percentage vaccination for her immunity is 83%-94% while for mumps it is 4-7 and 75%-86% respectively
