10 - Prevention Flashcards
Primary (1o) Prevention
the protection of health by personal and community-wide efforts with a focus on the whole population
• Objectives:
– To prevent new cases of disease occurring and therefore reduce the incidence of disease
• Where and How?:
– Population-level
– Individual level
1o Prevention at Population-level
• By reducing exposure to causal (risk) factors
- e.g., reducing smoking initiation in teenagers
• By adding a factor that prevents disease
- e.g., vaccination, water fluoridation
• Usually requires policy and/or legislation
- Smoking = tobacco taxes, restrictions on smoking indoors
- Physical activity = structural changes to the environment– sidewalks, walking paths, bike lanes (Town planning)
• Primary prevention at the population-level works best when it is driven by changes in societal attitudes
- e.g., drinking and driving, bikes lanes
1o Prevention at Individual-level
• By removing or lowering risk factors in at-risk patients
– Occurs at the patient-physician level
– Rationale behind the periodic health exam (PHE)
• e.g., smoking cessation counseling
• e.g., risk factor screening in at-risk patients (BP, BC, Physical inactivity, abdominal obesity)
• Distinction between primary prevention and secondary prevention hinges on the presence of existing disease
• Primary prevention = no existing disease
Secondary (2o) Prevention
measures available for the early detection and prompt treatment of health problems
• Objectives:
– To reduce the consequences of disease (death or morbidity) by screening asymptomatic patients to identify disease in its early stages and intervening with a treatment which is more effective because it is being applied earlier.
– It cannot reduce disease incidence
• Where and how do we screen?:
– Population-level or mass screening
– Individual-level screening or case finding
Screening – two different approaches
- population level screening
- individual level screening
• Population-level screening
– National level policy decision to offer mass screening to a whole sub-group of a population
• e.g., mammography screening
• e.g., Vision and hearing screening in primary schools
• Individual-level screening
– Occurs at the individual patient-physician level
– Also refereed to case finding
• e.g., BP screening every time you visit GP
– Focus is on identifying existing disease in patients who don’t know they have it.
Tertiary (3o) Prevention
• measures available to reduce or eliminate long-term impairments and disabilities, minimize suffering, and promote adjustments to irremediable conditions
• Objectives:
– To reduce the consequences of disease (esp. suffering) by treating disease and/or its direct complications in symptomatic patients.
• A proactive approach to medical care– may involve rehabilitative and/or palliative care
• Examples
• education about disease management (asthma)
• regular foot exams in diabetics
• pain management in hospice patients
Screening
- Objective: to reduce mortality and/or morbidity by early detection and treatment.
- Effective screening involves both diagnostic and treatment components
Pre-clinical Phase (PCP)
period between when early detection by screening is possible and when the clinical diagnosis would normally have occurred.
• Prevalence of PCP indicates how much early disease there is to detect
Lead Time
Lead time = amount of time by which diagnosis is advanced or made earlier
Sensitivity (Se)
the proportion of cases with a positive screening test among all individuals with pre-clinical disease
– Want a highly Se test in order to identify as many cases as possible…
Specificity (Sp)
the proportion of individuals with a negative screening test result among all individuals with no pre-clinical disease
Imperfect Sp affects many (the healthy), whereas an imperfect Se affects only a few (the sick)
Assessing the feasibility of screening
- Burden of disease: Effectiveness of treatment without screening
- Acceptability: Convenience, comfort, safety, costs (= compliance)
- Efficacy of screening: Test characteristics (Se, Sp), Potential to reduce mortality
- Efficiency: Low PVP, Risks and costs of follow-up of test positives, Cost-effectiveness
- Balance of risks (harms) vs. benefits
What makes an infection controllable?
• Relationship between symptoms and infectivity
• Healthcare can only respond to symptoms
– Quarantine, treatment, etc
Pathogens that are infectious following symptom onset are easiest to control
Issues surrounding vaccination
1• Reasons for vaccinating 2• Efficacy / Effectiveness 3• Logistical constraints (limited resources) 4• Ethical considerations 5• Behavioural aspects
- Reasons for vaccinating
• Direct benefit
– protection individuals against infection
• Indirect benefit
– invoking herd immunity
– don’t need to vaccinate everyone
– models can help estimate how much immunity in population is needed
- Efficacy / Effectiveness
- Not all vaccines are 100% effective or immediately effective
- Can be estimated using RCT or observational studies (confounding bias may be an issue)
- Logistical constraints (limited resources)
• Henderson ascribes success of smallpox eradication campaign to several factors:
1. Coordinated response across many countries
2. Vaccine could be kept at 37°C for a month, didn’t need refrigeration
– difficult to do in developing countries
3. Cases were highly symptomatic (rash) and easily identified
4. People in affected areas didn’t travel far, so had high success in finding further cases around an index case
- Ethical considerations
• Limited vaccines mean limited vaccinations
• Who should get vaccinated?
– those at high risk of complications if infected (immuno-compromised for e.g.)?
– groups of the population responsible for transmission? (e.g. school children)
– other targeting? (e.g. large households)
- Behavioural aspects
• The intension of individuals to seek treatment or follow control advice may change during an epidemic
Identifying optimal control options
– Minimize infection – Minimize transmission – Minimize death – Minimize other impacts of disease – Time to epidemic end – Reduce epidemic peak – Minimise social or economic impact – Eradication
