A 33-year-old man comes to the office for HIV testing after his partner was found to be HIV positive. The patient is asymptomatic and has no history of sexually transmitted infections. He has never had a previous HIV test. The patient has had several male and female sexual partners in his lifetime and uses condoms inconsistently. He does not use tobacco, alcohol, or recreational drugs. Vital signs are within normal limits and physical examination is normal. HIV testing is positive, and subsequent laboratory results are as follows:
| CD4 cell count | 420/mm3 |
| HIV viral load | 229,000 copies/mL |
| Hepatitis panel | |
| Hepatitis A antibody, IgG | positive |
| Hepatitis B surface antibody | positive |
| Hepatitis B surface antigen | negative |
| Hepatitis C virus antibody | negative |
| VDRL | nonreactive |
| Toxoplasma serology | negative |
| Tuberculin skin testing | 8-mm induration at 48 hr |
Complete blood count and liver aminotransferase levels are normal. Chest x-ray is unremarkable. In addition to starting antiretroviral therapy, which of the following interventions is most appropriate for this patient?
Tuberculin skin test (TST) thresholds | |
Induration size | Patient population |
≥5 mm |
|
≥10 mm |
|
≥15 mm |
|
PPD = purified protein derivative; TB = tuberculosis. | |
Approximately one third of the worldwide population has latent tuberculosis infection (LTBI). Although patients with LTBI who are not immunocompromised have a low lifetime risk (~5%-10%) of TB reactivation, those with HIV are significantly more likely (30- to 100-fold) to develop active disease due to impairments in immune signaling, activation, and coordination. Therefore, LTBI testing is recommended for all patients with newly diagnosed HIV. Either the tuberculin skin testing (TST) or interferon-gamma release assay (IGRA) can be used, but IGRA is generally preferred due to higher sensitivity/specificity and lower risk for anergy (false-negative result) at low CD4 counts.
A TST is considered positive in an HIV-infected individual when induration is ≥5 mm at 48-72 hours. Patients with positive LTBI testing require chest x-ray (infiltrate, lymphadenopathy) and symptom review (night sweats, fevers, cough) to rule out active TB. If no signs or symptoms of active TB are present, treatment with a rifamycin-based regimen (eg, rifapentine plus isoniazid weekly for 3 months) or 9 months of daily isoniazid plus pyridoxine is generally curative.
(Choices A and B) A positive TST indicates exposure to TB; repeating either TST or IGRA for confirmation is not recommended for high risk groups (eg, HIV positive). Because patients with HIV who have LTBI are at substantial risk for reactivation, monitoring with yearly chest x-ray would delay treatment and put the patient at significant risk for complications of infection; this patient should be treated for LTBI to prevent active TB.
(Choice C) Patients with advanced HIV (eg, CD4 count <200/mm3) often have false-negative initial TSTs due to anergy. Therefore, such patients are often retested after CD4 counts improve on antiretroviral therapy. Patients with positive initial testing require treatment, not retesting.
(Choices D and E) Chest x-ray and symptom review are sufficient to screen for active TB; a spiral CT scan is not cost-effective and would expose the patient to unnecessary radiation. Because this patient had a negative chest x-ray and symptom review, he should be treated for LTBI, not active TB.
Educational objective:
Patients with newly diagnosed HIV should be screened for latent tuberculosis infection (LTBI) with a tuberculin skin testing (TST) or interferon-gamma release assay. A TST with induration ≥5 mm is considered positive in this population. In the absence of active TB manifestations (positive chest x-ray, fever, night sweats, cough), treatment of LTBI with a rifamycin-based regimen (eg, rifapentine plus isoniazid weekly for 3 months) or 9 months of daily isoniazid and pyridoxine is curative.