In a healthy 29-year-old female nurse with a 12 mm purified protein derivative (PPD) skin test and no symptoms, what is the most appropriate management?

Treatment Recommendation for Healthcare Worker with Positive PPD

This 29-year-old healthcare worker with a 12 mm PPD should receive isoniazid 300 mg daily for 9 months (Answer C is closest, though 9 months is preferred over 6 months). 1, 2

Rationale for Treatment

PPD Interpretation in Healthcare Workers

• A 12 mm induration is definitively positive for healthcare workers, who are considered a high-risk group due to occupational exposure 3
• Healthcare workers with positive PPD results should be evaluated for preventive therapy regardless of age if they are recent converters or have occupational exposure risk 3
• The cutoff for a positive test in healthcare workers is ≥10 mm, making this result clearly positive 4

Age Considerations Favor Treatment

• At age 29, this patient is well below the age 35 threshold where hepatotoxicity risk becomes a primary concern 1
• The American Thoracic Society and CDC recommend treatment for all persons under age 35 with positive tuberculin tests, even without additional risk factors 1, 4
• Healthcare workers specifically should receive preventive therapy regardless of age due to their high-risk occupational exposure 3

Optimal Treatment Regimen

Preferred Option: 9 Months of Isoniazid

• Isoniazid 300 mg daily for 9 months is the gold standard regimen with the strongest evidence (A-II rating) 3, 2
• Nine months provides superior protection compared to 6 months, with maximal benefit in preventing progression to active TB 3, 2
• The protection conferred by 9 months of isoniazid is significantly greater than 6 months, though extending beyond 9 months to 12 months provides no additional benefit in HIV-negative individuals 3

Why Not the Other Options?

• Option A (no intervention) is incorrect because this patient has latent TB infection requiring treatment 1, 2
• Option B (3 months) is too short and not supported by any guideline 3, 2
• Option D (triple therapy) is for active TB, not latent infection, and would be inappropriate without evidence of active disease 2

Essential Pre-Treatment Steps

Rule Out Active TB First

• Perform chest radiography to exclude active tuberculosis before initiating treatment 2
• Conduct clinical evaluation for TB symptoms (cough, fever, night sweats, weight loss) 2
• Never start latent TB treatment without excluding active disease 2

Baseline Laboratory Testing

• Obtain baseline liver function tests, particularly given monthly monitoring recommendations 2
• While routine baseline testing is not mandatory for patients under 35, it provides a useful reference point 1, 2

Monitoring During Treatment

Monthly Clinical Assessments

• Educate the patient to stop medication immediately and seek care if symptoms of hepatotoxicity develop (nausea, vomiting, jaundice, abdominal pain, dark urine) 2
• Conduct monthly clinical evaluations to assess for hepatotoxicity symptoms 2
• For patients under 35 without risk factors, routine monthly laboratory monitoring is not required unless symptoms develop 1, 2

When to Withhold Treatment

• Stop isoniazid if transaminases exceed 3× upper limit of normal with symptoms 2
• Stop isoniazid if transaminases exceed 5× upper limit of normal without symptoms 2

Alternative Regimen

Rifampin as Second-Line Option

• Rifampin 600 mg daily for 4 months is an excellent alternative with less hepatotoxicity and better compliance (B-II evidence) 1, 2
• Consider this option if concerns about adherence to 9-month regimen exist or if early hepatotoxicity signs develop 1, 2

Common Pitfalls to Avoid

• Do not withhold treatment based solely on the 6-month option in Answer C - while 6 months is better than nothing, 9 months is the evidence-based standard 3, 2
• Do not delay treatment - healthcare workers are at ongoing occupational risk and should begin therapy promptly after active TB is excluded 3
• Do not forget pyridoxine supplementation (vitamin B6) to prevent peripheral neuropathy, though this is more critical in patients with risk factors like HIV, diabetes, or malnutrition 3