Letter to the Editor - Sputum sampling, storage and recovery: accuracy and sensitivity for Mycobacterium tuberculosis

Dear Editor,

The recent article by Pye et al. discusses the recovery of bacteria from sputum specimen samples stored at different temperatures (1). This article highlights sample handling, storage and transport, from the field to the clinical laboratory. This may be important in the field collection and identification of highly contagious and epidemiologically important microbes like Mycobacterium tuberculosis (MTB). Indeed, Tansuphasiri et al. found that positive cultures of MTB decreased significantly when stored at room temperature for 5 days compared with cultures from fresh specimens (2). Conversely, storage of MTB at low temperatures (-20 0C) for 2 months also increased bacterial lysis and decreased recovery (3). To date, research supports the use of molecular methods (e.g. polymerase chain reaction) the sensitive detection of small sample sizes of sputum collection bacterial (i.e. MTB) (4), and the shipping of sampling from rural, isolated areas for accurate molecular diagnosis is preferred methodology over sputum smears (5).

Kenneth Hoekstra
Assistant Professor
Western States Chiropractic College

References

1. A Pye, S L Hill, P Bharadwa, and R A Stockley Effect of storage and postage on recovery and quantitation of bacteria in sputum samples J Clin Pathol 2008; 61: 352-354

2. Tansuphasiri U, Chinrat B, Rienthong S.Evaluation of culture and PCR-based assay for detection of Mycobacterium tuberculosis from sputum collected and stored on filter paper. Southeast Asian J Trop Med Public Health. 2001 Dec;32(4):844-55.

3. Pathak D, Chakravorty S, Hanif M, Tyagi JS. Lysis of tubercle bacilli in fresh and stored sputum specimens: implications for diagnosing tuberculosis in stored and paucibacillary specimens by PCR. BMC Microbiol. 2007 Sep 4;7:83.

4. Guio H, Okayama H, Ashino Y, Saitoh H, Xiao P, Miki M, Yoshihara N, Nakanowatari S, Hattori T. Method for efficient storage and transportation of sputum specimens for molecular testing of tuberculosis. Int J Tuberc Lung Dis. 2006 Aug;10(8):906-10.

5. Tansuphasiri U, Boonrat P, Rienthong S.Direct identification of Mycobacterium tuberculosis from sputum on Ziehl-Neelsen acid fast stained slides by use of silica-based filter combined with polymerase chain reaction assay. J Med Assoc Thai. 2004 Feb;87(2):180-9.