Urgent need for a rapid microbiological diagnosis in critically ill pneumonia.

Severe lower respiratory tract infection is a common issue in Intensive Care Units that causes significant morbidity and mortality. The traditional diagnostic-therapeutic approach has been grounded on taking respiratory samples and/or blood cultures as soon as possible and starting empirical antibiotic therapy addressed to cover most likely pathogens based on the presence of the patient's risk factors for certain microorganisms, while waiting for the culture results in the following 48-72 hours to adequate the antibiotic treatment to the sensitivity profile of the isolated pathogen. Unfortunately, this strategy leads to use broad-spectrum antibiotics more times than necessary and does not prevent possible therapeutic failures. The recent development of rapid molecular diagnostic techniques, based on real time polymerase chain reaction (RT-PCR), makes it possible to determine the causative agent and its main resistance pattern between 1 and 5 hours after sampling (depending on each tecnique), with high precision, some of them reaching a negative predictive value greater than 98%, facilitating the very early withdrawal of unnecessary broad-spectrum antibiotics. Its high sensitivity can also detect unsuspected pathogens based on risk factors, allowing adequate treatment in the first hours of stay. This short review discusses the potential usefulness of these techniques in critically ill patients with lower respiratory tract infection and advocates their immediate implementation in clinical practice.