Module 6: Using the evidence Flashcards
What is epidemiology
The study of occurrence and distribution of health related events, states or processes in specified populations, including the study of the determinants influencing such processes and the application of this knowledge to control relevant health problems
What is public health
The science and art of preventing disease, prolonging life and promoting health through organised efforts of society
What is primary prevention
Interventions that attempt to prevent disease from occurring, i.e reduce the incidence of disease. E.g immunisation
What is secondary prevention
Interventions that attempt to reduce the impact of disease by shortening its duration, reducing severity or preventing recurrence. E.g cures, earlier treatments and diagnoses
What is tertiary prevention
Interventions that attempt to reduce the number or impact of complications and improve rehabilitation. E.g rehabilitation
What are the two strategies for primary prevention
High risk (individual) strategy: individuals in need are identified, preventive process controls level of exposure
Population (mass) strategy: reduce the health risks of the entire population
What are some examples of mass primary prevention
Increasing price of tobacco, regulation of salt content of foods, cycleways
What are the pros and cons of the mass strategy
Radical, large potential for whole population, behaviourally appropriate. Small benefit to individuals, poor motivation of individuals, benefit to risk ratio may be small
What are the pros and cons of the high risk strategy
Appropriate to individuals, individual motivation, clinician motivation, favourable benefit to risk ratio for individuals. Need to identify individuals, might be against population norms, can be hard to sustain behavioural change
What is the prevention paradox
A large number of people at small risk may give rise to more cases of disease than the small number who are at high risk. But a prevention that brings large benefit to the community may offer little to each participating individual
What is evidence based practice
Treatment taking into account patient values and choices, best available evidence and clinical expertise. Research provides the evidence to guide your practice, evidence is evolving, you need to know how to evaluate it
What is the lowest in the hierarchy of evidence
Anecdotes
What is the highest in the hierarchy of evidence
Systematic review and meta analyses
What are the best study designs to work out how common a disease is and who is most likely to get it
Cross sectional or cohort studies of incidence and prevalence
What are the best study designs to work out the causes of a disease
Cohort or case control
Diagnostic accuracy studies tend to be (study design type)
Cross sectional
What is the best study to work out the natural history of a condition (what happens if you do nothing)
Cohort
What are the best studies to work out the best treatment
RCTs
Why is good evidence vital
To prevent ineffective treatments, treatments for which the harms outweigh the benefits, fail to provide effective interventions
What is epidemiological surveillance
Ongoing systematic collection, analysis, interpretation and dissemination of data regarding a health event for use in public health action to reduce morbidity and mortality and to improve health. Ongoing descriptive epidemiology
What are the elements of surveillance
Data collection, analysis, interpretation, dissemination, action
What is surveillance used for
Characterising patterns of disease, detecting epidemics, further investigation, research, disease control programmes, setting priorities, evaluation
What are the two types of surveillance
Indicator based and event based
What is indicator based surveillance
Specific selected indicators are under surveillance (generally specific diseases/cancers), report on rates of disease by demographic characteristics of affected individuals
What is event based surveillance
Organised monitoring of reports, media stories, rumours, other information about health events that could be a serious risk to public health
What are the types of indicator based surveillance
Passive (most common), active, sentinel
What is passive surveillance
Relying on individuals to present with a disease. Routine reporting of health data: notifiable diseases, disease registries, hospital data
What are some examples of notifiable diseases (diseases which must be reported by law)
Measles, monkeypox
What is active surveillance
Serosurveillance: the monitoring of the presence or absence of specific substances in the blood serum of a population
Health survey
What is sentinel surveillance
Monitor diseases or trends, detect outbreaks. Selected institutions or groups provide health data. E.g testing someone for HIV when they came in to be tested for syphilis
What are the characteristics of a good surveillance system
Clear case definition, organised, workable/practical/simple, uniform, continuous, timely, sensitive, acceptable (to the public and key stakeholders)
What is screening
The widespread use of a simple test for a disease in an apparently healthy population
What is a screening programme
Organised system using a screening test among asymptomatic people in the population to identify early cases of disease in order to improve outcomes
What is a screening test
A test to test large numbers of apparently healthy people to identify individuals suspected of having early disease who will then go on to have further diagnostic tests to confirm the diagnosis. Differs from diagnosis test as there is greater emphasis on cost and safety and less on definitive diagnosis
Why try to detect early? (screening)
Example of secondary prevention, aim to limit consequences of disease through early diagnosis and treatment
What is the purpose of screening
To improve outcomes and reduce mortality. All screening programmes do harm, some do good as well
When should we screen
Consider seriousness of disease, ability to alter course of disease, lead time (longer lead time = more likely to detect disease early), prevalence of pre-clinical disease (must be high). Need to consider costs to benefits. Must improve quality of life (e.g diagnosed with something uncurable)
What is sensitivity in screening
Proportion of people with the disease which test positive
What is specificity in screening
Proportion of people without the disease who test negative
Want to maximise specificity and sensitivity but
There is a trade off between the two
What is the positive predictive value
Proportion of people who test positive and have the disease (true positive / all positives)
What is the negative predictive value
Proportion of people who test negative and don’t have the disease (true negative / all negatives)
Unlike specificity and sensitivity, PVs are influenced by
Disease prevalence in the population
What is lead time bias
Increasing the morbidity of a disease without reducing mortality
What is length bias
Diagnosing a disease that would never have become apparent.
What influences the spread of disease
Properties of the agent, sources of infection, biological reservoirs, host factors, exposure variation, environment
What is the epidemiological triangle
Host (who gets the disease): descriptive epidemiology
Environment (what conditions led to the disease): environmental investigation
Agent (what causes the disease): laboratory investigation
Immunity, transmission and survival
What are infectious agents
Bacteria, viruses, fungi, protozoa, helminths
What is infection
Entry of a microbiological agent into a higher order host and its multiplication within the host
What is infestation
External surface only
What is infectivity
Ability of an organism to invade and multiply in a host
What is pathogenicity
Ability of an organism to produce clinical symptoms and illness (proportion of those exposed who get ill)
What is virulence
Ability of an organism to produce serious disease (case-fatality rate)
What is direct transmission
Touching or inhaling infectious secretions
What is indirect transmission
Always involves a vehicle (fomites, food, water, animal, etc)
What is the infectious process
Infection, incubation period, clinical disease, recovery, immunity
Latent -> infectious period
What is an epidemic
Unexpected increase in the incidence of a disease (localised). Two or more cases identified from a common source, cases in excess of the expected number in a given time or place
What is an endemic
Constant presence of a disease or infectious agent within a geographical area or population group
What is a holoendemic
Constant presence of a disease or infectious agent within a geographical area or population group
What is a hyperendemic
Intense disease with time periods of no transmission
What is a pandemic
Disease affecting a large number of people across international borders
What is a cluster
Aggregation of relatively uncommon events or diseases in space or time that are thought to be greater than could be expected by chance. Usually rare, non-infectious. May have a suspected environmental cause. Many emerging diseases first become apparent in clusters
What is the secondary attack rate
Spread of disease from primary case to other (secondary) cases
What is the pattern of rate of infection
Slows down as more people become immune (around generation 3)
Why do we need to investigate outbreaks
Stop and prevent further illness, prevent further outbreaks from similar sources, address public concerns and involve public in disease control, reduce direct and indirect costs, identify new mechanisms of transmission of known diseases, identify new or emerging disease agents
What are the steps to outbreak investigation
Preparation, surveillance, confirmation, outbreak description, outbreak investigation (analytic epidemiology component, environmental component, laboratory component), outbreak control, outbreak communication, outbreak documentation
What is outbreak confirmation
Taking seasonal changes into account and decide if a spike in cases is unusual
What are the types of outbreaks
Common source (point source, continuous common source, intermittent source), propagated source (person to person), mixed (e.g point source then propagated person to person)
What does a common source epi curve look like
Normal distribution, not everyone exposed at the same time gets sick at the same time (differing incubation periods)
What does a continuous source epi curve look like
More continuous
What does a intermittent source epi curve look like
Clustered
What does a propagated source epi curve look like
Intermittent (one case to begin with), then exponential growth and decay
Surveillance vs screening
Fundamental purpose of surveillance is prevention, fundamental purpose of screening is clinical
What is the process of investigation of an outbreak
Examine cases, environmental scan for additional cases, look for more details by conducting detailed analysis for possible causes
What is geospatial mapping
Enables distribution of cases to be visually represented
What is the pandemic plan for Aotearoa
Plan for it, keep it out, stamp it out, manage it, recover from it
