Prevention Tiers 1–4
Primary = Prevent disease before it occurs (vaccines, smoking cessation). Secondary = Early detection in asymptomatic (screening tests). Tertiary = Reduce disability in established disease. Quaternary = Prevent overmedicalization.
Lung Cancer Screening
Annual Low-Dose CT (LDCT) for adults age 50–80 who have a 20 pack-year smoking history and currently smoke or quit within the past 15 years.
AAA Ultrasound Guideline
One-time screening abdominal ultrasound for men aged 65–75 who have EVER smoked (>= 100 cigarettes in lifetime).
Colorectal Screening
Universal screening begins at age 45 until 75 (Colonoscopy every 10 yrs, FIT annually). If first-degree relative < 60: start at age 40 or 10 yrs before diagnosis.
USPSTF Grade A & B Clinical Screening Guidelines Master Matrix
The US Preventive Services Task Force (USPSTF) establishes evidence-based screening recommendations tested extensively across all medical licensing exams:
| Target Malignancy / Disease | Target Population | Screening Modality | Screening Frequency & Discontinuation Criteria |
|---|---|---|---|
| Colorectal Cancer | Average-risk adults aged 45 to 75 | Colonoscopy (gold standard) OR Fecal Immunochemical Test (FIT) OR Cologuard (sDNA-FIT) | Colonoscopy every 10 years; FIT annually; Cologuard every 3 years; discontinue at age 75 (individualize 76–85) |
| Breast Cancer | Women aged 40 to 74 | Screening bilateral 2D/3D mammography | Every 2 years (biennial); clinical breast exam and self-exams are NOT recommended |
| Cervical Cancer | Women aged 21 to 65 | Ages 21–29: Cervical cytology (Pap smear); Ages 30–65: Cytology alone, hrHPV cotesting, or hrHPV alone | Ages 21–29: Every 3 years; Ages 30–65: Cytology q3y, hrHPV q5y, or cotesting q5y; stop at 65 if adequate prior negative screening |
| Lung Cancer | Adults aged 50 to 80 with ≥ 20 pack-year smoking history | Annual Low-Dose Computed Tomography (LDCT) | Screen annually; discontinue once individual has not smoked for ≥ 15 years or develops health problem limiting life expectancy |
| Abdominal Aortic Aneurysm (AAA) | Men aged 65 to 75 who have EVER smoked (≥ 100 lifetime cigarettes) | One-time Abdominal Duplex Ultrasound | One-time exam; surgical repair indicated if diameter ≥ 5.5 cm or expansion > 1 cm/year; not recommended in non-smoking women |
| Osteoporosis | Postmenopausal women aged ≥ 65 (or younger postmenopausal women with FRAX ≥ 8.4%) | Dual-Energy X-Ray Absorptiometry (DEXA) scan of hip and spine | T-score ≤ -2.5 defines osteoporosis; repeat interval guided by initial T-score (every 2–5 years) |
The 10 Steps of Epidemiologic Outbreak Investigation
CDC protocol for investigating infectious outbreaks and public health emergencies:
| Step Number | Investigative Action | Core Objectives & Board Traps |
|---|---|---|
| Step 1 | Prepare for field work | Assemble interdisciplinary investigative team, supplies, and legal authority |
| Step 2 | Establish the existence of an outbreak | Verify that observed number of cases significantly exceeds the expected baseline endemic incidence |
| Step 3 | Verify the clinical diagnosis | Review clinical findings and laboratory test results with microbiologists; rule out laboratory artifact |
| Step 4 | Construct a working case definition | Define objective criteria: Time, Place, Person, and Clinical/Lab features (Confirmed, Probable, Suspect) |
| Step 5 | Find cases systematically & record information | Active case finding across clinics and emergency rooms; compile line listing (demographics, onset date, exposures) |
| Step 6 | Perform descriptive epidemiology | Plot Epidemic Curve (Epi Curve): Point-source (sharp peak within one incubation period) vs. Propagated (steep progressive peaks person-to-person) |
| Step 7 | Develop hypotheses | Generate biologically plausible hypotheses regarding source, vehicle, and mode of transmission |
| Step 8 | Evaluate hypotheses analytically | Conduct analytical study: Cohort study (calculate Relative Risk) for well-defined populations; Case-Control study (calculate Odds Ratio) for ill-defined open populations |
| Step 9 | Implement control & prevention measures | CAN OCCUR AT ANY STEP; do NOT wait for study completion to halt contaminated food lots or recall products |
| Step 10 | Communicate findings | Publish written public health report; advise healthcare personnel and affected community |
Board Traps & Common Distractors
- In an epidemiologic outbreak investigation, control and prevention measures (e.g., recalling a contaminated food lot or closing a water well) MUST be implemented as soon as a source is identified; NEVER delay life-saving public health control measures to complete analytical hypothesis testing.
- Lead-time bias creates the false appearance of increased survival time caused by earlier diagnosis through screening without actually prolonging true survival from disease onset.
- Length-time bias occurs when screening preferentially detects slower-progressing, more indolent cases with inherently better prognoses, overestimating the clinical benefit of the screening program.