Nosocomial pneumonia (NP) severely complicates the course of mechanical ventilation. Although the need of an appropriate antimicrobial therapy adapted from the results of cultures from lower respiratory samples is well known, the best moment to start it is yet to be defined.

To assess the benefits of an appropriate antimicrobial therapy started just after the direct sample examination versus after the culture results.

A retrospective cohort study including 50 NP cases, diagnosed on clinical examination, bronchoalveolar lavage and protected specimen brush. Once the radiological and clinical characteristics of the patient have been analysed, the antimicrobial therapy modality is studied. Patients have been separated into two groups, depending on the delay before the antimicrobial therapy: just after the direct examination for group 1 (G1) and after the culture analysis for group 2 (G2).

For G1 the appropriate antimicrobial therapy is started with a delay of 4.6 ± 2.5 hours after the direct examination results, while for G2 this delay reaches 34.5 ± 22.5 hours. Hence, in 44 patients, initial antimicrobial therapy was appropriate straightway and in the remaining six patients was adapted on the results of culture. No differences have been noticed in terms of mortality (54% vs 53%, P = 0.91) and length of stay in the intensive care unit (28.7 days vs 19.3 days, P = 0.16) between the two groups. Both were similar regarding clinical and radiological diagnosis, age and severity of the NP. However, in G2, a significantly higher number of multi-resistant bacteria have been found (87% vs 73%, P < 0.001) as well as a higher rate of tracheal colonization within 48 hours after the fiberoptic bronchoscopy (76% vs 60%, P < 0.001).

For patients having a NP of moderate gravity, it is possible to wait for the culture before the start of antimicrobial therapy.