A 28-year-old woman with newly diagnosed pulmonary tuberculosis (sputum smear-positive, cavitary disease) is started on standard 4-drug therapy. Her husband, who is HIV-positive (CD4 count 180 cells/µL), is asymptomatic and has a negative tuberculin skin test (TST). What is the most appropriate next step for TB prevention in the husband?

Explanation

## TB Prevention in HIV-Positive Contacts with Low CD4 Count ### Clinical Context The husband is: - A close contact of an active TB case (wife with smear-positive, cavitary TB) - HIV-positive with CD4 <200 cells/µL (advanced immunosuppression) - TST-negative (likely due to anergy from severe immunosuppression) - Asymptomatic with normal CXR ### WHO/CDC Recommendations for TB Prevention in HIV | Scenario | CD4 Count | TST Result | Recommendation | |----------|-----------|-----------|----------------| | Contact of active TB | Any | Negative | IPT for 6 months | | Contact of active TB | Any | Positive | IPT for 6–9 months | | Non-contact, no TB disease | >200 | Negative | No IPT | | Non-contact, no TB disease | ≤200 | Negative | IPT for 6 months | | Non-contact, no TB disease | ≤200 | Positive | IPT for 6–9 months | **Key Point:** In HIV-positive individuals with CD4 <200 cells/µL who are contacts of active TB (regardless of TST status), isoniazid preventive therapy (IPT) for 6 months is indicated. TST anergy in advanced HIV does not exclude TB infection risk. ### Why IPT Now (Not Deferred) 1. **Close contact** with smear-positive, cavitary TB (high transmission risk) 2. **Severe immunosuppression** (CD4 <200) — cannot mount immune response to contain infection 3. **TST anergy** — negative TST does not rule out TB infection or risk; it reflects immune dysfunction 4. **Timing** — IPT should begin as soon as TB disease is ruled out, regardless of CD4 count **Clinical Pearl:** In HIV patients with CD4 <200 cells/µL, TST sensitivity is only 10–20% due to anergy. A negative TST does NOT exclude TB infection or the need for preventive therapy in contacts. **High-Yield:** IPT (isoniazid 5 mg/kg/day for 6 months) is safe and effective in advanced HIV and should be started immediately in contacts, even if CD4 is very low. Antiretroviral therapy (ART) should also be initiated urgently (CD4 <200 is an AIDS-defining condition). **Mnemonic:** **CONTACT + LOW CD4 = IPT NOW** — Do not wait for CD4 recovery or TST conversion in TB contacts with advanced HIV.