Survival of mycobacteria in sputum at different temperatures

In the course of prolonged transport of sputa suspected of the presence of mycobacteria, propagation of the present nonspecific microflora usually occurs, which results in a high number of contaminated cultivations and low cultivation positivity. This unfavourable phenomenon is especially encountered in tropical and subtropical countries with high mean yearly temperatures, where, in addition, the places of sputum collection are often at a great distance from the central laboratories. The present study, accordingly, tested the survival of mycobacteria and nonspecific microflora in sputa stored at 2 - 4 degrees C, 30 degrees C and 37 degrees C for 1 - 14 days. Over this time span the loss of cultivable mycobacteria was minimal at 2 - 4 degrees C, substantial (by 3 or 4 orders) at 30 degrees C, while at 37 degrees C, their complete destruction occurred between the 4th and the 8th day. The counts of nonspecific microflora, on the contrary, invariably increased by 1 or 1.5 order at the higher temperatures (30 - 37 degrees C) already in the first few days. The study led to the unequivocal conclusions that, for successful cultivation of sputum mycobacteria, the time of their transport should be as short as possible and the transport temperature the lowest possible. It is therefore recommended to use for sputum transport at longer distances boxes with good thermal insulation (walls of polystyrene or polyurethane) provided inside with freezing plates.