Interventions in Disease Prevention and Control – Comprehensive Bullet Notes

Classification of Interventions

• Two broad categories
  • Preventive interventions
  • Aim to stop disease from occurring → lower \text{incidence} (new cases)
  • Therapeutic interventions
  • Aim to treat, mitigate, or postpone effects once disease is under way → lower \text{case\ fatality\ rate} or reduce disability/morbidity
  • Some interventions possess dual preventive & therapeutic effects

2.1 Preventive Interventions

2.1.1 Vaccines

• Administered before natural exposure (usual case) to protect against infectious agent
• Mechanism
  • Induce humoral and/or cellular responses
  • Create immunological memory → long-term protection; boosters if interval to exposure is long
• Trial considerations
  • Enrol healthy individuals (often infants/children) unless disease exposure occurs later (e.g. STIs) or a novel agent emerges (e.g. new influenza strain)
  • Some vaccines given after exposure (e.g. anti-parasitic vaccines that limit proliferation; vaccines targeting parasite forms in vectors)
• Geographic sequence of trials
  • Initial trials usually in high-income countries (HICs) where vaccines are produced
  • LMIC trials still required due to different co-infections, nutrition, epidemiology
  • First efficacy trials for LMIC-specific pathogens (malaria, visceral leishmaniasis, TB, HIV) likely begin in LMICs

2.1.2 Nutritional Interventions

• Malnutrition (macro & micro) is a major cause/risk factor, esp. in low-income settings
• Trial types
  • Individual supplementation (high-protein/calorie diets; iron, folate, zinc, iodine, vitamin A, etc.) → repeated visits over years
  • Community-level fortification (e.g. iron-rich flour, iodized salt, vitamin D milk)
  • Agricultural or food-preparation modifications to boost nutrient intake

2.1.3 Maternal & Neonatal Interventions

• Maternal health during pregnancy/delivery is pivotal for maternal mortality & child outcomes
• Preventive components
  • Family planning, infection treatment (syphilis, malaria), balanced nutrition + micronutrients, antenatal monitoring, skilled birth attendance, postpartum care
• Trial settings
  • Community-based: early pregnancy detection, complication prevention
  • Facility-based: improve health-system performance around birth
• Neonatal examples: exclusive breastfeeding; kangaroo mother care (skin-to-skin, usually mother carrying preterm infant)

2.1.4 Education & Behaviour Change

• Some interventions entirely rely on behaviour change (anti-smoking, breastfeeding promotion)
• Educational input is universal but varies in intensity
  • Simple info (clinic times) → deep lifestyle change (diet, sexual habits)
• Behaviour change requires knowledge plus capacity, willingness & motivation
• Methodological notes
  • Often classified as complex interventions; necessitate formative community research (Ch. 9 & 15 methods)
• Example content areas
  • Hand-washing with soap (diarrhoea & respiratory infection reduction)
  • Adherence promotion for long-term regimens (HIV, TB)
  • Community participation for immunization/drug distribution, vector control, environmental improvements
• Trials are challenging; sustained change rarely achieved without multi-decade, multifaceted effort (e.g. smoking)

2.1.5 Environmental Alterations

• Aim: reduce transmission via environmental engineering
• Targets & measures
  • Water-borne / faecal–oral infections → latrines, sewerage, clean water, safe food storage
  • Air pollution → indoor/outdoor interventions; hazardous waste disposal
• Usually applied to entire communities → community or household = unit of randomization
• Require parallel education & lifestyle adaptation

2.1.6 Vector & Intermediate-Host Control

• Key for diseases transmitted via mosquitoes, tsetse, triatomines, sandflies, ticks, snails, etc.
• Control arsenal
  • Chemical: insecticides, larvicides
  • Biological: selective agents against vectors
  • Engineering: drainage, habitat reduction, housing/screen improvements
  • Community actions: eliminate breeding sites, deploy traps, combined strategies to delay resistance
• Evaluation
  • Process indicators (vector density) + health outcomes
  • Example (malaria):
  • Larval site control, repellents, residual indoor spraying (DDT on walls), insecticide-treated nets (ITNs)
  • Design nuances: residual spraying benefits neighbouring households → needs near-universal coverage; ITNs provide personal + community protection
  • Trials typically cluster-randomized; risk of inter-cluster contamination through vector flight

2.1.7 Drugs for Prevention (Chemoprophylaxis / Pre-emptive Therapy)

• Modes
  • Prevent infection (e.g. isoniazid in HIV+ to prevent TB)
  • Slow disease progression (ARVs in HIV)
• Delivery models
  • Individual diagnosis vs. group/mass administration (anti-helminthic to schoolchildren; fluoride in water; medicated salt)
• Strategy choices
  • Mass vs. targeted treatment; influenced by prevalence & cost-effectiveness
• Constraints: duration of drug action, adverse reactions, potential for resistance
• Examples
  • Anti-malarials for short-term travellers vs. pregnant residents
  • Annual praziquantel to school-age children → near elimination of severe Schistosoma\ mansoni outcomes

2.1.8 Injury Prevention

• Injuries = major death/disability cause in LMICs; heavy burden on youth & economy
• Leading types: road traffic, drowning, fires, poisoning, violence, war
• Possible interventions: traffic calming, pedestrian separation, secured water sources, etc.
• Research gap: few RCTs; high demand for rigorous trials

2.2 Therapeutic Interventions

2.2.1 Treatment of Infectious Diseases

• Most drugs kill/inhibit pathogen replication
• Strategy: case detection ⇒ treatment ⇒ reduced morbidity/mortality & possibly reduced transmission
• Success contingent on
  • High case-finding coverage (sensitive definition + diagnostics)
  • Case-holding (patient follow-up), especially for TB, leprosy

2.2.2 Surgical & Radiation Treatments

• Usually tested via clinical RCTs; field trials rarer but feasible (e.g. cataract extraction, hernia repair)
• Blinding issues: sham operations possible in some contexts; often open-label design required

2.2.3 Diagnostics to Guide Therapy

• Accurate, affordable, user-friendly diagnostics are critical
  • Sensitivity, specificity, predictive values directly affect intervention impact
• Example: rapid diagnostic tests (RDTs) for malaria → replace microscopy/presumptive therapy; spotlight non-malarial fever management
• Diagnostic performance studies = specialised design (Peeling et al., 2010)

2.2.4 Control of Chronic Diseases

• May be infectious (HIV, TB) or non-infectious (CVD, cancers)
• Management demands:
  • Behaviour change + daily pharmaceuticals
  • Community screening, staging, lab tests, long-term monitoring systems
• Trials often multi-year/decade to capture true efficacy

2.3 Other Forms of Intervention

2.3.1 Legislation, Legal Action, Taxation & Subsidies

• Laws & fiscal tools strongly shape behaviour (e.g. tobacco/alcohol taxes curb consumption)
• Difficulty of randomized evaluation: interventions usually nation-wide → scarce control groups
• Emerging conditional cash transfers & performance incentives
  • Examples: pay families for children’s school attendance; incentivize providers for quality care
  • Some assessed via RCTs; more potential exists

2.3.2 Health Systems Interventions

• Focus on system-level levers: policy, financing, education reform, leadership/governance
• Historically rolled out without rigorous evaluation
• RCT feasibility improved via stepped-wedge (phased introduction) designs (Brown & Lilford, 2006)
• Many qualify as implementation research or complex interventions

2.3.3 Implementation Research

• Objective: optimize delivery of already efficacious interventions in real-world contexts
• Examines practical, contextual challenges & cost-effectiveness
• Example trial: comparing clinic-based vs. home-based delivery of antiretroviral therapy with lay workers (Jaffar et al., 2009)

2.3.4 Complex Interventions

• Contain multiple interacting components (education, behaviour, service change)
• Challenges
  • Standardizing delivery, context sensitivity, logistical complexity, lengthy causal chains
• UK MRC Framework (2000, revised) outlines stages: Development → Piloting/Feasibility → Evaluation → Reporting → Implementation
  • Key questions across stages (Box 2.1): clarity of goals & theory, adequacy of piloting, choice of design (parallel, cluster, stepped-wedge), process & economic evaluation, detailed reporting, strategy for scale-up & monitoring
  • Poor attention to any stage weakens intervention quality & evaluability

Key Epidemiologic Metrics (formulas)

• Incidence: Incidence = \frac{\text{New\ cases\ in\ period}}{\text{Population\ at\ risk\ during\ period}}
• Case-Fatality Rate: CFR = \frac{\text{Deaths\ from\ disease}}{\text{Diagnosed\ cases}} \times 100\%

Ethical, Philosophical & Practical Considerations

• Transferability: Efficacy in HIC trials may not translate to LMICs (co-infections, nutrition, epidemiology differences)
• Equity & Access: Maternal/neonatal, environmental, vector control, and injury-prevention trials often aim to reach marginalized groups
• Resistance: Overuse of prophylactic drugs may accelerate drug-resistant organisms
• Community Engagement: Essential for behaviour change, environmental improvements, vector control, and complex interventions; poor engagement → trial failure
• Blinding & Placebo Ethics: Particularly delicate in surgical/radiation or community-wide interventions
• Long-Term Monitoring: Needed for chronic disease control & post-implementation surveillance of complex interventions