Tuberculosis screening

Screening for active tuberculosis is needed to make sure that people with active TB, especially in their lungs, are treated promptly and efficiently. It is also needed to make sure that people are not given prophylactic treatment in the presence of active TB, since this would only serve to generate drug-resistance. Active TB in people with HIV frequently presents outside the lungs and can take atypical forms.

TB screening may be prompted when people with HIV are admitted to hospital, including women giving birth, to prevent onward transmission to other people with HIV, patients and staff, as well as to ensure proper treatment.

Chest X-rays are of obvious value wherever tuberculosis is a major HIV-related public health problem, but must always be used in conjunction with other tests.

Culture of tuberculosis requires more specialised facilities and growth media which may or may not be available.

Protocols for TB diagnosis in the presence or absence of chest X-rays and with different levels of laboratory facilities have been published by WHO and local protocols should be developed, implemented and audited in line with national guidelines.

Alongside screening for active TB, people with HIV should be tested for latent TB, using a PPD skin test for past infection. In many settings, it is now clear that people who test positive can benefit from a course of treatment with isoniazid for six months, to prevent active disease.

One problem with skin tests is that people who are immunosuppressed often test negative, even though they are infected with the TB organisms. Sometimes positive results may be induced because of recent BCG vaccination rather than genuine TB exposure. (Indeed, this is one reason why BCG vaccine is not generally used in the USA.) Another problem is that they require a second clinic visit or contact with a trained health worker to read the test.

New tests are therefore being developed and evaluated, including PCR-based tests (like HIV viral load tests). Other tests may be based on immune responses to TB components such as an ELISPOT test which measures cellular immune responses to a protein which is found in TB but not in BCG. This has the advantage that it can be carried out on a stored blood sample and so does not require a second clinic visit.

Diagnosing other HIV-related infections

Some HIV-related conditions, such as Kaposis sarcoma, are often clinically obvious and do not necessarily require laboratory facilities for diagnosis.

An ophthalmic microscope is needed to assess CMV retinitis which can be a seriously disabling condition in late-stage HIV disease.

Many conditions do at least require access to light microscopy, staining materials and, in the case of most bacterial infections, laboratory culture facilities.

Ideally, there should be access to CT (computed tomography) scanning and/or MRI (magnetic resonance imaging), particularly to assess the extent of suspected brain tumours and lesions.