Viral Community-acquired Pneumonia

Abstract

Viruses as a cause of community pneumonia have been overlooked by clinicians. The reasons are that they were poorly investigated and difficult to diagnose. In recent years, by combining the use of classical and new polymerase chain reaction techniques, viruses may account for 10% to 40% of community-acquired pneumonias (CAPs) depending on the type of population studied. The most frequent viruses causing CAP are influenza A and B, adenovirus, and respiratory syncytial viruses. Usually, there are not many clinical features that could distinguish between viruses and bacteria. However, it has been observed that there are lower leukocyte counts and C reactive protein levels in viral CAP. Viruses can be isolated alone or in combination with classical bacteria such as Streptococcus pneumoniae. In this case, the severity of clinical presentation is worse. The diagnosis of viral CAP has improved substantially with the implementation of nucleic acid amplification tests, which are sensitive and specific techniques, providing, in addition, rapid results. The new array technology may detect up to 20 different respiratory viruses plus usual bacterial pathogens. The clinical course of viral CAP is usually benign but it is not the case with mixed pneumonias in which the mortality in severe CAP may reach up to 20%. Owing to this, feature systematic and rapid diagnosis of viruses is probably indicated in severe CAP patients (ICU admitted) in whom specific antiviral treatment could have beneficial effects.