Diagnostic procedures in ventilator-associated pneumonia: Microbiological and molecular methods as well as diagnostics in invasive pulmonary aspergillosis

Ventilator-associated pneumonia (VAP) is one of the most important nosocomial infections in the intensive care unit (ICU). Knowledge of the typical spectrum of bacterial pathogens causing VAP guides the diagnostic steps, whereby specific host factors must be taken into account. Therefore, in the presence of immunosuppression the probability for rare causative agents such as viruses or fungi is increased. The recommendations for diagnostic tests for VAP focus on classical microbiological methods, such as Gram staining and bacterial cultures. In this context molecular diagnostics take on an important role. While the polymerase chain reaction (PCR) for individual pathogens, primarily viral agents, is well-established and without any alternative in the daily clinical routine, multiplex PCR systems are gaining in interest. These tests provide the possibility of the simultaneous detection of all relevant bacterial pathogens with important antibiotic resistance genes as well as some viruses; however, due to a lack of evidence with respect to the improvement of clinical endpoints, multiplex PCR tests cannot currently be recommended for the routine use as a diagnostic tool in VAP. The diagnostic modalities of invasive pulmonary aspergillosis (IPA) in non-neutropenic mechanically ventilated patients in the ICU show some special characteristics. While in these cases, unlike in neutropenic patients, computed tomography (CT) of the chest reveals mostly unspecific findings, a crucial diagnostic component is the determination of the galactomannan (GM) antigen in bronchoalveolar lavage fluid (BALF) as opposed to the determination of the GM antigen in serum.