Preventive Medicine Flashcards

A county health department conducts a cohort study comparing lung cancer incidence between uranium miners and a matched control population over 20 years. The relative risk is 3.8 (95% CI: 2.1–6.9). Which measure would BEST quantify the public health burden attributable specifically to occupational radon exposure in this population?

Answer: Population attributable risk percent (PAR%)

The Population Attributable Risk Percent (PAR%) estimates the proportion of disease in the total population (not just the exposed) that can be attributed to the exposure, accounting for the prevalence of exposure in the population. This is the most useful metric for public health planning and policy because it reflects the overall burden that could be eliminated by removing the exposure. AR_e only quantifies risk among exposed individuals; SMR compares to a reference population but does not isolate attributable burden; NNH is more relevant to clinical interventions.

A 58-year-old female physician is evaluated for fitness for duty after returning from a 6-month humanitarian mission in sub-Saharan Africa. She reports no symptoms. Her tuberculin skin test (TST) converts from 0 mm to 14 mm. She received BCG vaccine in childhood and has a documented negative TST 2 years ago. What is the MOST appropriate next step?

Answer: Chest X-ray; if negative, initiate treatment for latent TB infection (LTBI)

A TST conversion (≥10 mm increase within 2 years) in a healthcare worker with documented prior negative TST is highly significant for true Mycobacterium tuberculosis infection, regardless of childhood BCG history (BCG effects on TST wane significantly after 10–15 years). IGRA can be used but is not mandatory to confirm — the documented conversion from a verified baseline in a high-exposure setting is sufficient. The correct next step per CDC/USPHS guidelines is a chest X-ray to rule out active TB; if negative, initiate LTBI treatment. The preferred regimen in 2026 is 3HP (rifapentine + isoniazid weekly × 12 doses) or 4R, but the question stem focuses on the management decision, not regimen selection.

During a systematic review of mammography screening trials, an analyst notes that the trials with shorter follow-up periods show a larger reduction in breast cancer mortality than those with longer follow-up. Which bias MOST likely explains this finding?

Answer: Lead-time bias inflating apparent mortality benefit in short-term trials

Lead-time bias occurs when screening detects disease earlier in its natural history, making survival appear longer (or mortality appear lower) without actually altering the disease course. In short-term trials, screened patients who are diagnosed earlier appear to survive longer simply because the clock starts earlier — mortality events may not yet have occurred by the end of follow-up. As follow-up lengthens, the mortality curves converge as the postponed deaths accumulate, diminishing the apparent benefit. Length-biased sampling is a real phenomenon in screening but would tend to persist over time rather than diminish with follow-up. Overdiagnosis would reduce apparent mortality in the screened group but would not explain a time-dependent attenuation.

A state epidemiologist investigates a cluster of 11 cases of Vibrio vulnificus septicemia over 6 weeks, all among adults who consumed raw oysters from a single licensed estuary. Water temperatures were documented at 28°C. The estuary tested negative for fecal coliforms. Which preventive intervention has the STRONGEST evidence for reducing Vibrio vulnificus mortality risk at the individual level?

Answer: Advising high-risk individuals (liver disease, immunocompromised) to avoid raw shellfish entirely

Vibrio vulnificus causes fulminant septicemia almost exclusively in individuals with underlying liver disease (cirrhosis, hepatitis), hemochromatosis, diabetes, or immunosuppression — with case fatality rates exceeding 50% in these groups. The strongest individual-level preventive measure with evidence-based support is counseling high-risk individuals to completely avoid raw shellfish. While HPP, temperature controls, and cold-chain management are effective regulatory/supply-chain interventions that reduce Vibrio burden in shellfish, they do not eliminate the risk to a zero threshold. At the individual clinical level, absolute avoidance in high-risk patients is the most impactful recommendation.

A 45-year-old male construction worker presents for a OSHA-mandated periodic medical surveillance evaluation. He works with crystalline silica. Spirometry shows FVC 81% predicted, FEV1 78% predicted, FEV1/FVC ratio 0.82. Chest X-ray shows bilateral upper lobe small rounded opacities, ILO category 1/1. He is asymptomatic and works in a state with no specific crystalline silica standard. Which of the following represents the MOST appropriate occupational medicine action?

Answer: Notify OSHA of the finding and recommend immediate worksite air sampling with exposure controls review

ILO category 1/1 opacities represent early simple silicosis — a sentinel health event that, under OSHA's General Duty Clause (and the 2018 OSHA crystalline silica standards where applicable), obligates the employer to evaluate and control silica exposures. The most appropriate immediate action is to notify OSHA (or trigger the employer's medical surveillance reporting obligation) and ensure urgent air monitoring and engineering controls review at the worksite — protecting other workers at risk. Removal from exposure is not automatically mandated at ILO 1/1 in all guidelines (unlike category 2/2 or progressive massive fibrosis), but the exposure must be quantified and controlled. HRCT is often used for characterization but is not the primary occupational medicine action. Smoking cessation alone is insufficient.

A preventive medicine specialist is asked to evaluate the cost-effectiveness of adding a universal newborn screening program for severe combined immunodeficiency (SCID) using T-cell receptor excision circle (TREC) assay. The program costs $15 per test, detects 1 case per 58,000 births, and early treatment with hematopoietic stem cell transplant (HSCT) achieves 94% survival vs. 40% without screening. The calculated incremental cost-effectiveness ratio (ICER) is $48,000/QALY. Which statement BEST characterizes the policy decision threshold?

Answer: The program falls below commonly used thresholds of $50,000–$150,000/QALY and is generally considered cost-effective

An ICER of $48,000/QALY falls below the conventional US willingness-to-pay (WTP) threshold range of $50,000–$150,000/QALY that is widely used in health technology assessment, making SCID screening cost-effective by standard criteria. The $50,000/QALY figure (derived from early kidney dialysis cost analyses) is often cited but represents the lower bound; many US payers and academic frameworks accept up to $100,000–$150,000/QALY. The GDP-per-capita threshold (~$63,000 in 2026) is a WHO-derived heuristic used more in global health contexts and is not the standard US policy benchmark. Dismissing ICER for rare diseases is incorrect — QALY-based analysis is actually particularly important for rare conditions where clinical volume is low but treatment benefit is high.