[Current techniques used for the diagnosis of respiratory virus infectious in intensive care units]

Hundred viruses can be isolated in patients suffering from respiratory virus infections and hospitalised in intensive care unit (ICU): influenza virus, respiratory syncytial virus, para-influenza virus, adenovirus, coronavirus, rhinovirus, enterovirus, human metapneumovirus, bocavirus… Nasal or tracheobronchial specimens, which contain many epithelial cells will be used to isolate these common viruses. In immunocompromised patients a bronchoalveolar lavage has to be added to these specimens in order to detect cytomegalovirus and some adenovirus. The immunofluorescence or immunoenzymatic assays, which detect viral antigens in the infected cells are the easiest and fastest diagnostic methods, theoretically. As with other techniques, specimen quality is a major determinant of their performance. Unfortunately, the sensitivity of the antigen detection assays is low in respiratory infections in adults. Then the virus recovery by cell culture, which is usually more sensitive than the antigen detection assays, can be helpful. Many studies have reported more respiratory virus detections using nucleic acid testing such as PCR. They detect viruses, which are missed by conventional methods and increase the detection of common respiratory virus. Multiplex PCR assays have been developed, and these can simultaneously detect several viruses directly in clinical specimens. Nucleic acid testing can subtype viruses using subtype-specific primers, and analyse strain variation through genetic. It can be used also to quantify the viral load in clinical specimens. More recently real-time RT-PCR assays have been developed to get more rapidly the results of the nucleic acids assays. Specimen quality, timing and transportation conditions may be less critical for nucleic acid testing than for culture or antigen detection, as viable virus and intact infected cells need not to be preserved. Moreover, viral nucleic acids are detectable for several days longer into the clinical course than is cultivable virus, potentially allowing a diagnosis to be made in late-presenting patients. However, in a clinical virology laboratory, where the speed, low cost, and high sensitivity of the methods are required, the sequential use of antigen detection tests and multiplex PCR could be the best choice, particularly in the clinical setting of respiratory virus infections in adults hospitalised in ICU. In the future, the development of real-time multiplex PCR is likely to be top-priority.