SMF to Improve Performance of Microscopy for the Diagnosis of PTB in a High HIV Prevalence Setting

TB is a disease caused by a bacterium called Mycobacterium tuberculosis that can affect the lungs or other parts of the body. In most of the world and in Mbarara, Uganda, the method of diagnosis that is used is AFB smear microscopy. This method is widely available, inexpensive and rapid. However, this method's ability to truly detect people having TB is poor. That is, if someone has TB, the test results may say that they are negative, leading to delays in diagnosis, disease progression, and an ongoing transmission of the bacteria.

The new test for TB diagnosis we are studying is called the Small Membrane Filtration (SMF) method. This test that is being compared to the method currently being used and is very similar to the one that is currently used (standard smear microscopy) but has the advantage of concentrating the sputum (mucus) so that we can more easily see if bacteria are present in the sputum. It is hoped that a better way of knowing if someone has TB will help doctors decide when people need to be treated for TB and when not, which will improve the health of patients and help avoid passing the infection to others.

This study will enroll 740 HIV-infected and 310 HIV-uninfected adults with culture confirmed pulmonary TB. These individuals will be identified prospectively at two TB clinics in Mbarara, Uganda.

Study hypothesis: The investigators will assume that one sputum sample will be equivalent to two (null hypothesis) with respect to sensitivity unless we have evidence that the use of two has higher sensitivity (alternative hypothesis). The investigators will assume that SMF is equivalent to AFB smear with respect to sensitivity and specificity unless the investigators find evidence it is superior. The investigators will assume that SMF is equivalent to Xpert unless the investigators find evidence that Xpert is superior.

Inclusion criteria

• Adult (≥18 years)
• Pulmonary TB suspect defined as any person who presents with a productive cough for more than 2 weeks AND accompanied by at least one other respiratory symptom (shortness of breath, chest pains, hemoptysis) and/or constitutional symptom (loss of appetite, weight loss, fever, night sweats, and fatigue) (6).
• Willing to undergo TB evaluation and spontaneously expectorate ≥2 mL of sputum
• Willing to be tested for HIV, if no results available within past 6 months

Exclusion criteria

• Too ill or unable to provide written consent
• Treated with TB drugs for more than 3 days
• Extra-pulmonary or disseminated TB without pulmonary involvement (i.e. no cough)