Latent and Subclinical Tuberculosis in HIV Infected Patients

A Cross-sectional Study

Meaghan M Kall; Katherine M Coyne; Nigel J Garrett; Aileen E Boyd; Anthony T Ashcroft; Iain Reeves; Jane Anderson; Graham H Bothamley

Disclosures

BMC Infect Dis. 2012;12(7) 

In This Article

Background

In 1998, the World Health Organization recommended detection of latent tuberculosis infection (LTBI) in HIV infected individuals in order to institute preventive treatment.[1] Currently, in resource constrained settings, isoniazid preventive therapy is recommended for those likely to have LTBI, but research is required to evaluate the role of tests to identify tuberculosis (TB) and LTBI.[2] Interferon-gamma release assays (IGRAs) have a higher sensitivity in patients with lower CD4 counts and greater specificity in those from areas with a low incidence of TB than the tuberculin skin test; although in active disease the sensitivity is still about 80%.[3] The T-SPOT®.TB (immunospot) assay may have a higher sensitivity with fewer indeterminate results in immunosuppressed patients than the QuantiFERON-TB Gold.[3] This may be because the immunospot uses a fixed number of peripheral blood mononuclear cells and should therefore be less affected by the CD4 lymphocyte count.

In low TB burden countries, the role of IGRAs in screening HIV infected individuals has yet to be established. The United States Center for Disease Control guidelines advocate testing for LTBI at HIV diagnosis regardless of TB risk category[4] whereas UK national guidelines suggest an approach based on region of origin, CD4 count and length of time on antiretrovirals.[5] However, there are limited data on the utility of IGRAs as a screening tool in a low incidence clinical setting and on the management of positive results.[6–8]

Homerton University Hospital is situated in Hackney, London with an HIV prevalence five times the national average (825 versus 164 per 100,000 population),[9] and annual TB incidence four times the national average (58 versus 15 per 100,000 population).[10] The area has high numbers of migrants from sub-Saharan Africa. Over a third of the HIV patient cohort is from high tuberculosis burden countries, as defined by WHO criteria.[11] Approximately two thirds were diagnosed with HIV at a late stage of infection (CD4 < 350 cells/μl). The aims of this study were to evaluate the use of an IGRA in screening for latent or symptomless active TB in a cohort of patients with HIV infection, and to determine the completion rate of preventive treatment in patients with positive tests.

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