Comparison of two bacteriophage tests and nucleic acid amplification for the diagnosis of pulmonary tuberculosis in sub-Saharan Africa.

SETTING

National reference laboratory in Zambia, a high-incidence setting with a high prevalence of HIV infection.

OBJECTIVE

To compare the performance of a commercial bacteriophage kit with a nucleic acid amplification kit and an 'in-house' bacteriophage method for rapid diagnosis of pulmonary tuberculosis (TB).

METHODS

Sputum specimens from suspected pulmonary TB cases were examined by direct fluorescence microscopy and culture on Löwenstein Jensen (LJ). In a blinded study, remaining samples were tested by AMTD and FASTPlaqueTB or an in-house bacteriophage assay. Two specimen decontamination protocols were investigated.

RESULTS

Microbial contamination of 40.4% was observed when using the FASTPlaqueTB kit specimen preparation protocol. When compared to culture on LJ, the sensitivity of the FASTPlaqueTB test was 20.7%. Implementation of a modified Petroff's decontamination protocol reduced contamination to 5.8% and the FASTPlaqueTB test detected 8/25 (32%) of culture-positive specimens. The sensitivity of AMTD and smear microscopy for these specimens were 64% and 48%, respectively. In a separate experiment the sensitivity of an in-house bacteriophage assay was 45.3% compared to 64.2% for AMTD and 45.3% for direct smear microscopy.

CONCLUSIONS

Additional analysis of sputum specimens by bacteriophage assay provided no advantage in this setting. For the rapid diagnosis of TB, AMTD offered improved sensitivity over direct smear microscopy.