Public Health Microbiology Flashcards
Epidemiology
The study of how diseases occur, spread and are controlled.
A good surveillance system
- Systematic collection of relevant data
- Collation and evaluation of data
- Prompt dissemination of findings to those who can take appropriate action
What is morbidity ?
The condition of suffering from a specific disease or medical condition.
E.g, the levels of air pollution are associated with increased morbidity from respiratory diseases
What is mortality ?
The number of deaths that a specific illness or health condition has caused.
Mortality rate
The number of deaths normalised by population, usually in a given period of time
How did epidemiology begin ?
Miasma theory dominant
- Epidemics of cholera and typhoid caused many deaths in major cities in Europe
- Recording of deaths via the ‘Bills of Moratlity’
- John Snow opposed the miasma theory - believed that water was the source of cholera
Surveillance of infectious diseases
- Who gets infected ?
E.g, sex, age, occupation - Where are those who become infected ?
E.g. travel abroad - When did infection occur ?
E.g. incubation period, seasonal trends
Incidence of a condition
The number of new cases diagnosed in a population in a given period - usually one year.
Prevalence of a condition
The total number of people who have the condition at a particular point in time, regardless of how long they have been affected
Sporadic
A single episode of infection e.g, case of tetanus
Endemic
The disease habitually present within a given geographical area. Population is constantly exposed to infection from birth onwards. E.g, common cold in UK
Epidemic
The occurrence in community or region of an outbreak of illnesses in excess of normal expectancy and derived from a common source.
E.g, whooping cough and measles in the UK
Pandemic
Worldwide spread of disease e.g, influenza 1918
When is an epidemic not an epidemic ?
When there are more cases but is kept o expected levels from morbidity data
Activities following occurrence of a notifiable disease
- Isolation of patients (perhaps)
- Contacts of patients traced
- Carriers of organism must be found
- Epidemiological studies undertaken to find source of outbreak
- Immunisation programmes introduced where possible to prevent further spread or recurrence
- Specifc measure such as withdrawal of food product or closure of food premises
Point source outbreak
Single social function e.g. party
Common source outbreak
People eating at the same restaurant or food outlet over a period of time
Cohort study
When people become ill at a particular function e.g, point source outbreak
Attack bites
Define groups of people who ate each food & compare rates of illness between groups to identify the suspect vehicle
Calculating relative risk
RR = Attack rate for those exposed / Attack rate for those not exposed
Nationwide Salmonella outbreak
- Performed case-control study (12 cases, 19 controls)
- Questioned about date of onset of illness, symptoms, and what they had eaten in the previous 3 days
- Statistical analysis of data — calculated probability that particular food is implicated in outbreak (Fisher exact test), accept result if p is smaller or equal to 0.05.
Notifiable disease surveillance
- Passive
- Investigator waits for a disease report from health-care providers, laboratories, and others who are requested/required to report these diseases to the public health agency
Aims of vaccination
- To protect individuals
- To protect vulnerable or at risk individuals
- To achieve ‘population immunity’
3 broad approaches to vaccination policy
- Voluntary
- Incentivised
- Quasi-mandatory
