In addition, many laboratories use panels of antibodies to common respiratory viruses, thus permitting the screening of clinical specimens for many viruses at once. For instance, the respiratory antigen panel routinely includes influenza and parainfluenza viruses, adenovirus, and respiratory syncytial virus. In addition, antigen detection assays remain positive for several days to weeks after viable virus can no longer be detected in culture. This feature is useful in the evaluation of patients who present late after the onset of symptoms or patients who have received prior treatment with antiviral agents. The disadvantage of viral antigen detection methods is that, overall, their sensitivity is lower than that of viral cultures.
Sensitivity also varies depending on the virus sought.
It is always recommended, therefore, that antigen detection methods be used in conjunction with cell culture for optimal diagnosis of viral infections. PCR has become especially useful for the detection of cytomegalovirus in various body fluids, such as blood, urine, and respiratory secretions. Unfortunately, owing to the latent nature of cytomegalovirus, its detection does not necessarily prove it to be the pathogen responsible for the associated disease. PCR detection should be used in combination with viral culture and immunocytologic and histochemical staining. Summary Despite enhanced laboratory techniques such as viral culture, rapid antigen detection, and gene amplification, a confident diagnosis of viral pneumonia continues to be a challenge.