Effect of storage and postage on recovery and quantitation of bacteria in sputum samples

Abstract

Aims: The aims of the study were to compare bacterial recovery following storage of sputum samples at 20oC room temperature and 4oC (refrigerated) for 24 hours, and to determine the effect of postage on viable bacterial numbers. Methods: A total of 38 individual sputum samples from clinically stable patients with bronchiectasis were split into 3 equal aliquots and quantitative bacterial culture was performed either immediately, following storage at 4oC for 24 hours or following storage at 20oC for 24 hours. A further 42 sputum samples were split into two equal aliquots and quantitative bacterial culture was performed either immediately or following postage back to the laboratory by first-class mail from an outside location. Results: The predominant organism could still be recovered following storage at both 4oC and 20oC, but viable numbers were significantly reduced following storage at 4oC (p<0.004) by at least an order of magnitude (ten-fold) in 24% of samples stored at 4oC compared to only 8% stored at 20oC. Posting samples back to the laboratory did not affect the recovery of bacterial species and there was no difference in viable numbers isolated. Conclusions: The results suggest that storage at room temperature is preferable to refrigeration as it retains both the species isolated and the viable number. The data also confirms that sputum samples can be posted to the laboratory from patients in the community without affecting qualitative or quantitative results.