HIV weakens the immune system making an infected person more vulnerable to tuberculosis. The risk of a HIV positive person to develop active TB is 5-15% per year vs. 10% lifelong for a non-infected person. Not only does HIV increase the risk of reactivating latent Mycobacterium tuberculosis, but it also increases the risk of rapid TB progression soon after infection or re-infection. As the CD4 lymphocyte count declines, the risk of active TB further increases to reach levels of between 15-20% per annum in patients with CD4 cell counts less than 200 cells/uL.

The algorithm for the diagnosis of smear-negative pulmonary TB is to include HIV status, severity of AIDS and TB, and early use of Chest radiography (an indispensable diagnostic tool) in the decision tree. During the pre-HIV years of TB control its use became restricted indeed for cases who had signs and symptoms of TB, but whose sputum was repeatedly negative. This situation changed dramatically when the implications of TB / HIV co-infection became well known and evidence based.

HIV positive TB patients have more often negative sputum and diagnosis then relies on Chest X-ray and clinical judgment. In addition, early mortality in TB/HIV co-infected patients is common and can only be prevented by rapid and early diagnosis of TB, a process in which the Chest X-ray is an essential tool. WHO Stop TB has acknowledged the need for a shift in the place of the Chest X-ray in combating TB and HIV mortality. Chest X-ray shortens delays in diagnosing TB and non-TB chest diseases common among people living with HIV. Co-infected patients with signs and symptoms may die before sputum or culture are available. When using Digital Radiology, Chest images are instantly available and abnormalities consistent with TB can be detected on the spot. However, patients with CD4 cell counts less than 200 cells/uL show less typical abnormalities in their Chest image.

TB Intensified Case Finding (ICF) is a core activity to identify TB-suspects, for whom active TB needs to be ruled out or confirmed. Furthermore, ICF strategy is going to be expanded to strengthen identification of TB suspects and break the chain of transmission, especially among people living with HIV. For those who are appropriately screened for TB (including a Chest X-ray) and have no active TB, Isoniazid Preventive Therapy (IPT) is a recommended and proven intervention to prevent development of clinical TB. The Tanzania TBHIV policy proposes IPT as an intervention in the care of PLHIV. Chest –X ray screening of eligible persons for IPT is a cornerstone of the intervention.

In the TB screening process the Chest X-ray (CXR) is an indispensable tool in PLHIV, for whom sputum is often negative. Physicians dealing with PLHIV may have limited knowledge and experience in the interpretation of CXR.

With decentralization of HIV Care and Treatment to the District Hospital (DH) and Health Centre (HC) level more X-ray facilities required with an increasing number of clinical staff needing to be trained in CXR diagnosis of TB and HIV related conditions. In fact, several international trials have shown that the diagnostic performance of CXR could improve when a well-defined Chest Reading and Recording methodology is used to read the films, a system of CXR quality control is in place and the X-ray reader knows the underlying information of the patients, such as treatment history, age or HIV status. Digital radiology in combination with Computer Aided Diagnosis to detect images TB suspect have the potential to assist (remote and on site) the less experienced readers in diagnosing TB more effectively.

 

 

More publications by Dr. Jan van den Hombergh on the fight against co-infection in Eastern Africa can be found at: http://siteresources.worldbank.org/EXTAFRREGTOPHIVAIDS/Resources/TB-HIV-TEXT-Online.pdf