Proposal of an easy method to improve routine sputum bacteriology

The study of bacterial flora of the lower respiratory tract is very important for the diagnosis of pulmonary infections and proper therapy but it has to face important methodologic problems. The main problem is contamination of the sputum during its passage through the upper airways. The present study suggests an improved procedure aiming first of all at reducing the specimen contamination by upper airway bacteria by means of a preliminary mouth wash, and secondly at comparing qualitative and quantitative cultures of spit with those of sputum. In our study bronchial lavage aspirate (BLA) cultures were used as a control. Both definite (80 patients) and random (20 patients) sequence sampling procedures were considered to show the importance of a correct sequential specimen collection. Bacteria isolated in the sputum and/or in BLA but absent in the spit were considered the most probable responsible for an eventual pulmonary infection. On the contrary a germ found in the spit and eventually in the sputum but not in BLA was considered responsible for only an eventual inflammation of the upper respiratory tract. Doubtful cases were solved by comparing the different bacterial concentrations in the various samples. A preliminary mouth washing procedure decreased the mean concentration of contaminants in the sputum: 3.6 +/- 7.5 x 10E8 (E = exponent) versus 3.7 +/- 7.2 x 10E7 CFU/ml spit versus sputum (80 patients) p less than 0.001. On the contrary if sputum preceded spit (12 out of the 20 randomly treated subjects), bacterial counts were not significantly different (2.1 +/- 5.7 x 10E8 vs. 1.3 +/- 2.9 x 10E8 CFU/ml, respectively, p = NS). In the group of correctly treated patients (80 subjects) only infrequently oral contaminants were found in BLA (12.5%). The finding of bacteria in BLA but absent in spit and/or sputum was rare (4.8%) suggesting that, at least in chronic obstructive lung disease (COLD) patients, spit and sputum quantitative and qualitative cultures may be sufficient for a good microbiologic examination in almost all the cases.