Tuberculosis diagnostics in Fiji: how reliable is culture?

Settings: Acid-fast bacilli (AFB) smear microscopy and Mycobacterium tuberculosis culture are the first-line diagnostic tests for tuberculosis (TB). The contamination of TB cultures significantly reduces the reliability of TB diagnosis.

Objective: To investigate factors associated with TB culture contamination in Fiji, and the relative diagnostic performance of culture compared to microscopy.

Design: All tests performed at the Daulakao Mycobacterium Reference Laboratory (DMRL) in Fiji from 2010 to 2012 were reviewed. Study variables included AFB smear and TB culture results, age and type of specimen, referring TB testing centre and patient age.

Results: Of 5708 specimens reviewed, 70% had both AFB smear and culture results recorded; 421 specimens were contaminated; 2.7% of specimens were either degraded or had no result recorded. There was moderate agreement (κ = 0.577) between the two tests. Culture was more likely to be positive at higher AFB smear scores. Culture contamination was associated with distance from the DMRL, sample age and operator-associated factors.

Conclusion: Increases in the speed of referral from TB testing centres or the addition of preservatives to sputum specimens may results in less culture contamination. The planned introduction of liquid culture techniques in combination with culture on Ogawa media is likely to increase the sensitivity of TB diagnosis in Fiji.