Extrapulmonary TB (EPTB) accounts for nearly 30% of TB cases in HIV endemic settings, such as South Africa. The diagnosis of extrapulmonary TB is complicated by the poor performance of Gene Xpert and TB Culture in extrapulmonary fluid (30-50% sensitive), as well as the poor specificity of ADA. We can therefore not reliably use these tests to diagnose EPTB as effectively as we use them in sputum samples. The current best practice for diagnosing pleural TB is to perform a pleural biopsy, which is both invasive and costly. A rapid, easy to use test is needed to allow accurate and fast diagnosis of EPTB. Interferon-gamma is released at high concentrations in extrapulmonary fluid in active EPTB. Antrum Biotech has developed the IRISA-TB assay (validated and SAHPRA licenced) for the diagnosis of EPTB.

The study will assess the real-world performance of IRISA-TB compared to ADA, Gene Xpert, and TB Culture when used to diagnose EPTB. We will evaluate IRISA-TB's performance in the following patient groups:

• Suspected TB pleural effusion (n= 650)
• Suspected TB pericardial effusion (n= 280)
• Suspected TB peritonitis (n= 200)
• Suspected TB meningitis (n = 1040) As part of our evaluation, we will ask clinicians who treat these patients to provide their feedback on IRISA-TB. We will ask them to indicate to what extent the IRISA-TB test helped them to make treatment decisions. Finally, we will conduct an economic assessment to determine the true cost of diagnosing and treating EPTB to the health system and patients, and we will determine how IRISA-TB could potentially result in cost savings.

Inclusion Criteria:

1. Male or female participants 18 years and over attending health care facility with symptoms of TB.
2. Serosal or CSF fluid sample provided to NHLS with sufficient volume to perform SOC tests + 1ml.
3. Patients in whom extrapulmonary TB is part of the treating clinicians' differential diagnosis.

Exclusion Criteria:

1. Volunteers who refuse to sign informed consent and/or provide clinical details (Proxy consent will be obtained for participants who are incapacitated, with a follow up consent when they have recovered their capacity to consent)
2. Patients with current significant history of substance or alcohol abuse that may impact study visits.
3. Patients who are unable to communicate by telephone or who do not have a current active traceable contact number.
4. Patients not willing to undergo an HIV test.
5. Patients whose fluid sample volumes are insufficient to perform standard of care testing in addition to IRISA-TB
6. Positive sputum GXP within 2 weeks prior to serosal fluid or CSF sampling.