Much attention has been given to ventilators, respiratory tubing and humidifiers as sources of bacteria causing pneumonias in intensive therapy unit (ITU) patients. However, efficient decontamination and safe storage of ventilators and humidifiers between patients, with frequent changing of respiratory tubing and the use of Chlorhexidine in humidifier reservoirs, are now undertaken in most ITUs. In addition, chest aspiration, which is an important route for bacterial entry to the chest, is performed by trained ITU staff, who are well aware of this danger and wear gloves and use meticulous techniques. As a result, it can be argued that infection of the lungs in ITU patients from these sources and routes has reached an “irreducible minimum.”

Unfortunately, many patients in ITUs continue to develop pneumonias. In my own experience patients yielded Pseudomonas in tracheal aspirates as frequently after the introduction of these techniques, together with the insertion of efficient bacterial filters, between the patient and the ventilator in both the inspiratory and expiratory lines, as before their adoption. What other sources and routes of infection of the lungs should be considered?