Diagnostic relevance of the semi-quantitative method for tracheal aspirates analysis

Ventilator-associated pneumonia is a frequent disease among intensive-care patients receiving mechanical ventilation. Accurate microbiological diagnosis is crucial for adequate antibiotic treatment, thus reducing mortality. Samples taken from tracheal aspirates are a suitable option for the recovery of the microorganism, responsible for this pathology. The objective of this work was to evaluate the efficacy of the semi-quantitative method for the microbiological analysis of tracheal aspirates, compared to the quantitative method. Negative results in samples analyzed through the semi-quantitative method corresponded exactly with those analyzed through the quantitative method. The same correspondence was observed with samples presenting 4+ using the semi-quantitative method, 81 out of 90 samples 4+ resulted in more than 10(6) CFU/mL, bacterial counts in the 9 remaining samples were between 10(5)-10(6) CFU/mL using the quantitative method. These results validate the ability of the semi-quantitative method to precisely detect negative samples as well as those presenting a 4+ consistent growth, which were, certainly, positive. However, some difficulty has been observed regarding 2+ and 3+ events, catalogued as a "grey zone" given that none of them allowed a similar precise result compared to the quantitative method. Processing of tracheal aspirates in a semi-quantitative manner would be a feasible diagnostic strategy to confirm or discard any infectious process when quantitative techniques are not viable. This is only possible in those cases whose results are either negative or 4+ (read as positive).