Performance of OMNIgene.SPUTUM (DNA Genotek) and cetylpyridinium chloride for sputum storage prior to mycobacterial culture

Purpose. The aim was to assess the performance of both cetylpyridinium chloride (CPC) and OMNIgene.SPUTUM (OMNI) reagents for the maintenance of Mycobacterium tuberculosis viability in sputum prior to recovery by culture.

Methodology. Using 312 sputa, we evaluated the performance of the two reagents using culture on Lowenstein-Jensen medium after sputum storage in CPC or OMNI for up to 28 days. In addition, the viability of M. tuberculosis isolates stored in both reagents was assessed.

Results. The contamination rates for freshly processed samples and those stored in CPC were not statistically different, while the contamination rate for OMNI was significantly lower than that for fresh sputa (P=0.026 for 8 days and P=0.002 for 28 days of storage). The culture positivity for fresh sputa (81.7 %) was similar to that for samples stored in CPC, regardless of the storage time (89.8% for CPC-8 and 73.0% for CPC-28). For OMNI-preserved samples, the culture positivity was similar after 8 days of storage (84.2 %), but decreased significantly after 28 days (42.7 %; P

Conclusion. Culture from sputum stored for 8 days at room temperature in OMNI or CPC gave comparable culture positivity rates to culture from fresh sputum, but after 28 days of storage the performance of OMNI decreased significantly compared to CPC.