Viral Pneumonia

Viral pneumonia is defined as a disease entity wherein there is the viral causation of oxygen and carbon dioxide gas exchange abnormalities at the level of the alveoli, secondary to viral-mediated and/or immune response-mediated inflammation. The traditional role of viral pneumonia was as a disease found predominantly in the very young, the elderly, and those exposed to influenza. In the past, the diagnosis of viral pneumonia was predicated on it being somewhat a diagnosis of exclusion. History, physical exam, chest radiography, and available lab work (until recently) lacked sensitivity and specificity. Once bacterial pneumonia has been excluded, then viral pneumonia diagnosis was entertained.

Traditionally, the treatment of viral pneumonia revolved around supportive care:

1. Supplemental oxygen when indicated

2. Airway augmentation as appropriate

3. Monitoring of and replacement of any fluid deficits

4. Symptomatic control of temperature and cough

5. Rest to reduce oxygen demand

6. Treatment of any comorbidities and/or concomitant bacterial pneumonia

The concepts of diagnosis, prevalence, clinical role, and treatment of viral pneumonia are in flux for several reasons.

1. There is a growing population at increased risk of viral pneumonia:

1. The increases in life span and early infant survivability have created an additional population at greater risk of viral pneumonia.

2. The increased number of those receiving immune-impairing therapy (radiation and/or chemotherapy) for cancer.

3. The increased use of disease-modifying hematological/immunological agents in chronic illness, resulting in secondary impaired immunity.

4. The advent of HIV

5. The increase in the number of patients with inborn immune impairment serving bacterial infection secondary to antibiotic therapy.

6. The increased incidence of organ transplantation and immunosuppressive therapy.

2. The availability of sensitive, specific, real-time-result-available testing for viral entities:

1. Polymerase chain reaction (PCR) technology is replacing viral cultures and serial viral antigen titers. Both viral culture results and serial antigen testing were problematic because test results were not available until weeks after the acute illness, and viral culturing for pneumonia could involve invasive sampling techniques to acquire.

2. The availability of PCR testing has resulted in increased testing in general.

3. The mechanism of PCR itself is more sensitive and specific because many viruses are notoriously difficult to grow in culture and are very sample dependent.

3. The positive feedback loop that results from improved viral pneumonia testing modalities:

1. The test availability results in an increased number of diagnoses.

2. The increased number of diagnosis raises the clinical index of suspicion for the entity.

3. The increased clinical index of suspicion raises the number of tests ordered.

4. The availability of safe, tolerable, and somewhat specific antiviral therapies:

1. Prior viral pneumonia treatment was essentially supportive measures only.

2. Initial efforts at antiviral therapy were not well tolerated.

3. The availability of some specific and effective treatments now spur earlier testing and a greater appreciation of the role of viral infection in pneumonia.

4. Disease-modifying therapy for HIV is now available.

5. The increasing role of viral pathogens in pneumonia and the increased realization of the role of bacterial and viral co-infection necessitate a higher clinical index of suspicion and early identification of viral pulmonary pathogens. Counterbalance seeing this new clinical burden is the availability of the following:

1. Enhanced laboratory detection via ELISA and PCR testing modalities

2. Enhanced radiographic detection for a high thin section CAT scan

3. An increasing number of safe and efficacious antiviral drugs

4. Increased recognition of the role of prevention in viral infectious disease.