It is important to keep in mind that our study evaluated a theoretical model, performed on the data retrieved from a cohort of patients who were mechanically ventilated, which compared two different strategies in the management of ventilator-associated pneumonia (VAP). This comparison was based on the data retrieved during our surveillance study, when it was extrapolated at the time of the clinical diagnosis of VAP. The duration of appropriate therapy was established to be 10 days in all cases; death of patients was not taken into account. There were fewer antimicrobial-days with the ETA-based strategy because in those cases in which the result of the ETA coincided with the final microbiologic diagnosis of VAP, the result could have been no therapy at all in the ETA-guided therapy, if the result was negative, compared with 2 days of three antimicrobials (this is 6 antimicrobial-days) if the group had received American Thoracic Society/Infectious Diseases Society of America (ATS/IDSA) guideline-guided therapy. In the great majority of the cases, the therapy suggested by the surveillance cultures was appropriate for the actual pathogen of VAP and required fewer antimicrobial-days than would be necessary in a guideline-based approach. The guideline approach relies on deescalation, and, thus, between 2 and 4 antimicrobial-days would be added, compared with using therapy-guided ETA surveillance cultures. Finally, in those cases in which the therapy based on ETA surveillance cultures was totally or partially inappropriate, the initial prescription would be replaced by a new antimicrobial therapy for 10 days, adding 10 to 20 antimicrobial-days to the one, two, or three antimicrobials administered inappropriately during the first 2 days (2, 4, or 6 antimicrobial-days); in this instance, the sum of antimicrobial-days could be greater, the same, or even less than the number of antimicrobials received if the therapy had been guided by the ATS/IDSA guidelines.