In a 78‑year‑old asymptomatic woman with a positive QuantiFERON‑Gold interferon‑gamma release assay and a normal chest radiograph, what is the recommended treatment for latent tuberculosis infection and the next management steps?

Treatment of Latent Tuberculosis Infection in a 78-Year-Old Woman

This 78-year-old asymptomatic woman with a positive QuantiFERON-Gold test and normal chest X-ray has latent tuberculosis infection (LTBI) and should be offered treatment, with the preferred regimen being rifapentine plus isoniazid once weekly for 12 weeks under directly observed therapy. 1, 2

Confirm the Diagnosis

Your patient meets the diagnostic criteria for LTBI, which requires three elements:

• Positive immunologic test (QuantiFERON-Gold) 1, 3
• Negative evaluation for active disease (normal chest radiograph, no symptoms) 1, 3
• Exclusion of active TB by history, physical examination, and radiography 1

Do not perform sputum examination in this asymptomatic patient with a normal chest X-ray—sputum testing is not indicated for most persons being considered for LTBI treatment and would be wasteful. 4, 5 Sputum examination is only required if she has respiratory symptoms (chronic cough >3 weeks, hemoptysis, night sweats, fever, weight loss) or an abnormal chest radiograph. 4, 5

Risk Assessment and Treatment Decision

Treatment should be strongly recommended for this patient. Although the lifetime risk of progression from LTBI to active TB in immunocompetent persons is approximately 5-10%, treating LTBI prevents progression to active disease, which carries substantial morbidity and mortality. 1 The benefits of LTBI therapy outweigh the risks when properly monitored, and all individuals with documented LTBI should be offered treatment regardless of age. 1

At 78 years old, age alone is not a contraindication to treatment. 1

Recommended Treatment Regimens

First-line option (preferred):

• Rifapentine 900 mg plus isoniazid 900 mg once weekly for 12 weeks as directly observed therapy 1, 2
• This regimen offers superior completion rates due to shorter duration 1

Alternative regimens if rifapentine is unavailable or contraindicated:

• Isoniazid 5 mg/kg (maximum 300 mg) daily for 9 months 1
• Isoniazid 5 mg/kg daily for 6 months (acceptable but slightly lower efficacy) 1
• Rifampin 10 mg/kg (maximum 600 mg) daily for 4 months (for patients unable to tolerate isoniazid) 1

Do NOT use the 2-month rifampin-pyrazinamide regimen—this is no longer recommended due to high risk of severe hepatotoxicity, including cases requiring hospitalization and resulting in death. 1

Pre-Treatment Evaluation

Baseline Laboratory Testing

Obtain baseline liver function tests (AST/ALT and bilirubin) if your patient has any of these risk factors: 1

• Pregnancy or within 3 months postpartum
• HIV infection
• Chronic liver disease (hepatitis B/C, cirrhosis)
• Regular alcohol use
• Concurrent use of other hepatotoxic medications

Routine baseline liver testing is NOT required for healthy adults without these risk factors. 1

HIV Testing

Offer HIV testing to this patient, as HIV infection markedly increases the risk of progression to active TB and the urgency of treatment. 1, 5 If she is HIV-positive and has any respiratory symptoms, sputum examination would be required even with a normal chest radiograph. 4, 5

Drug Interaction Review

Review all current medications for potential interactions with rifamycins, which are potent inducers of hepatic cytochrome P450 enzymes. 2

Monitoring During Treatment

Clinical Monitoring

Monthly clinical visits are required throughout treatment: 1

• Assess medication adherence
• Evaluate tolerance and adverse effects
• Screen for symptoms of hepatotoxicity at each visit 1

Educate the patient to immediately stop medication and seek urgent medical evaluation if she develops: 1

• Abdominal pain
• Nausea or vomiting
• Jaundice
• Dark urine
• Unexplained fatigue

Laboratory Monitoring

Periodic liver function testing is indicated for patients with: 1

• Abnormal baseline results
• Any of the risk factors listed above
• Development of symptoms suggestive of hepatotoxicity

Discontinue treatment immediately if: 1

• AST/ALT >3× upper limit of normal with symptoms
• AST/ALT >5× upper limit of normal without symptoms
• Bilirubin rises above the normal range (regardless of symptoms)

Important Caveats

Do NOT repeat the QuantiFERON test after treatment completion—the test typically remains positive even after successful LTBI treatment and provides no useful information about treatment efficacy or cure. 1, 6 Studies show 85-88% of patients remain QuantiFERON-positive after preventive therapy, with comparable IFN-gamma responses before and after treatment. 6

Do NOT perform a tuberculin skin test (TST) now that you have a positive QuantiFERON result—both tests should prompt the same evaluation and management. 1

Ensure active TB is definitively excluded before starting single-drug LTBI treatment. Never initiate monotherapy until active disease has been ruled out. 4, 1