HIV TB

World wide TB is the most common cause of death in people with HIV About 1/3 of HIV infected people worldwide are co-infected with TB (co-infection rates differ: sub-Saharan Africa 75%, Australia –very low) Patients with HIV are at a greater risk of: – Reactivating latent infection (7-10% annually vs. 5-10% lifetime risk in non-HIV people) – 10-20% likely to acquire TB from open contact (vs. 5-10%) – Developing progressive primary disease (30-40% vs. 5-10%) – Developing disseminated, miliary or extrapulmonary disease (>60% vs. <25% in non-HIV people) – Developing second episode of TB from exogenous infection

Clinical presentation CharacteristicAdvanced HIV infection **Early HIV infection Pulmonary : extra pulmonary disease 50:5080:20 Clinical presentationOften resembles primary TB Often resembles post- primary TB Chest radiograph Intrathoracic lymphadenopathy CommonRare Lower lobe involvementCommonRare CavitationRareCommon Tuberculin anergyCommonRare Sputum smear positivityLess commonCommon Adverse drug reactionsCommonRare Relapse after treatmentCommonRare ** CD4 T lymphocyte count < 200/mm3

Dx of TB in HIV All patients with active TB should be tested for HIV. Diagnosis difficult due to (particularly in advanced HIV): – Frequently negative sputum smear findings – Atypical radiographic findings – Higher prevalence of extra-pulmonary TB at inaccessible sites – Resemblance to other opportunistic pulmonary infections In patients with late stage HIV and low CD4 count diagnosis is usually made by mycobacterial culture of blood, bone marrow or tissue.

Rx of TB in HIV co-infection Rx consists of four drugs (isoniazid, rifampicin, pyrazinamide + ethambutol) for the first two months. Once sensitivities are confirmed pyrazinamide and ethambutol are withdrawn, the other two are continued for 4 months. In some cirumstances Rx maybe extended beyond 6 months (extrapulmonary TB). Rifampicin has pharmacokinetic interactions with protease inhibitors (PI) and non- nuclease reverse transcriptase inhibitor (NNRTIs) – via cytochrome p450. There are also overlapping toxicities between HAART and anti – TB drugs: in particular hepatotoxicity, peripheral neuropathy and GI side effects. Therapeutic principles in HIV TB: – Anti TB treatment takes precedence over HAART for HIV – In patients already on HAART, the same has to continue with modifications both in HAART and anti- TB treatment. – In patients not on HAART, the need and timing of initiation are based on the short term risk of disease progression and death, CD4 count and type of TB, on an individual basis. Treatment should be supervised (DOTS). MDR occurs in about 6% of cases of TB in HIV positive individuals.