Performance of a rapid phage-based test, FASTPlaqueTB, to diagnose pulmonary tuberculosis from sputum specimens in South Africa

Abstract

Setting: Twelve primary health care clinics in the South Peninsula Administration, Cape Town, Western Cape Province, South Africa.

Objective: To evaluate the performance of FAST-PlaqueTB, a new phage-based test, for the rapid diagnosis of TB in individuals with no previous history of TB treatment presenting at primary health care clinics in Cape Town, South Africa.

Design: A comparative study of FASTPlaqueTB, auramine smear microscopy and Lowenstein-Jensen culture of 1692 decontaminated sputum specimens from 853 patients suspected of having TB. Resolution of discrepant results was undertaken by review of clinical information, chest X-ray and follow-up of treatment outcomes.

Results: FASTPlaqueTB detected TB in 75.2% of culture-confirmed cases and 70.3% of all cases with a clinical diagnosis of TB, with a specificity of 98.7% and 99.0%, respectively. The performance parameters of FASTPlaqueTB were significantly superior to those of concentrated auramine smear microscopy (63.4% and 61.3% sensitivity, and 97.4% and 97.3% specificity in culture-confirmed and all cases, respectively). Of those patients with two negative sputum smears, FAST-PlaqueTB detected TB in 54.1% of TB cases confirmed by culture and 48.8% of all cases with a clinical diagnosis of TB. A combination of smear microscopy and FASTPlaqueTB enabled 81.2% of culture-confirmed cases and 78.4% of total TB cases to be detected within 2 days of presentation.

Conclusion: FASTPlaqueTBTM is a rapid, manual test for the diagnosis of TB. The test has significantly higher sensitivity overall compared with auramine sputum smear microscopy in individuals with no previous history of TB treatment, although smear microscopy did detect the most infectious of the TB cases. The FAST-PlaqueTB test is easy to perform, requires no dedicated equipment, and results are read by eye within 48 hours. This test can be useful for the diagnosis of TB in developing countries with a high burden of TB where other rapid diagnostic tests may not be appropriate. The test shows promising performance, particularly in the diagnosis of smear-negative disease, and could be used in conjunction with smear microscopy to aid in the diagnosis of additional cases of TB.