Viral Pneumonia

Introduction

Respiratory viruses are common causative agents of pneumonia, particularly in certain groups of patients (1). The most common respiratory pathogen causing respiratory tract infections is the influenza virus, especially during the colder months, although respiratory syncytial virus (RSV) and parainfluenza viruses are also common (2, 3). Respiratory viruses are a common cause of community-acquired pneumonia, which is generally associated with milder clinical symptoms (4). The course of virus-induced lung inflammation (viral pneumonia) depends on the virus as well as the patient's age and underlying diseases and may result in death.

Epidemiology

Viral pneumonia is less common in young and middle-aged adults but occurs much more frequently in children and the elderly. Studies investigating the etiology of pneumonia have found that 13–50% of diagnosed cases of community-acquired pneumonia in children are of viral origin (5). Viral infections are identified in 15–29% of adults with pneumonia (6, 7).

Individuals with compromised immune systems, which may develop after chemotherapy or radiation therapy, during the treatment of chronic inflammatory diseases with immunosuppressive medications, or following organ transplantation, are more susceptible to viral pneumonia. Viral pneumonia is also more common in patients with acquired immune deficiency syndrome (AIDS) or congenital immune deficiency. Certain underlying conditions may predispose individuals to viral pneumonia, including poorly controlled diabetes, injuries, severe burns, malnutrition, and poverty.

The modes of viral transmission depend on the specific virus (Table 1). Influenza viruses, rhinoviruses, and RSV are among the most easily transmitted.

Table 1. Modes of Transmission of Viral Pneumonia (8)

Pathophysiology

After inhalation, most viruses tend to multiply in the epithelium of the upper respiratory tract and subsequently infect the lungs through the respiratory tract. The extent of lung tissue damage varies depending on the virus. Some viruses, particularly cytopathic viruses, directly damage bronchial epithelial cells or pneumocytes, whereas others trigger an abnormal immune response to the pathogenic process (10, 11).

Pneumonia can develop through three mechanisms: direct entry of the pathogen into the lungs (RSV, influenza virus), spread of infection to the respiratory tract from nearby foci of infection in the upper respiratory tract (measles), or hematogenous spread from distant foci of viral infection (CMV).

Viruses damage pneumocytes and lead to alveolar injury. When the alveolar interstitium is damaged, inflammation, secondary edema, and microhemorrhages occur, and a cellular immune response is activated.

Diagnosis

Unlike bacterial pneumonia, viral pneumonia has no pathognomonic findings in the medical history or physical examination. However, certain features may suggest viral pneumonia:

• gradual development of symptoms rather than sudden onset;
• lower (subfebrile) body temperature;
• less purulent sputum;
• history of immunosuppression;
• previous upper respiratory tract viral infection;
• AIDS;
• history of organ transplantation or blood transfusion;
• cancer;
• accompanying influenza symptoms;
• accompanying gastrointestinal symptoms.

During physical examination, the following findings may suggest viral pneumonia:

• disproportionately rapid heart rate or respiratory rate relative to body temperature;
• the increase in body temperature is disproportionately low compared with the degree of general weakness;
• accompanying upper respiratory tract infection;
• cough is usually dry, although after 1–2 days a productive cough may develop, with expectoration of yellow or green sputum;
• rash;
• bilateral lung involvement.

Children with viral pneumonia often have a poor appetite and wheezing, and their skin and lips may appear bluish due to insufficient oxygen. In patients over 65 years of age, low body temperature, dizziness, or even confusion are common.

Since medical history and physical examination findings are not specific enough to establish a diagnosis of viral pneumonia, laboratory and radiological investigations are necessary. Viral pneumonia is not typically characterized by a significant increase in the white blood cell count or a left shift in the leukocyte differential.

Biochemical blood tests are necessary to determine the degree of dehydration and assess kidney function, particularly before prescribing medications that may affect renal function. C-reactive protein (CRP) concentrations may be elevated in viral pneumonia, although a greater increase in CRP is more characteristic of bacterial infection.

ELISA (enzyme-linked immunosorbent assay) can identify certain pathogens, including herpes simplex virus, RSV, influenza A and B viruses, and cytomegalovirus. Polymerase chain reaction (PCR) testing can also help identify the cause of viral pneumonia. Cytological examination may not always establish the diagnosis. Depending on the type of virus (RNA or DNA virus), this examination may reveal inclusions in different locations within the cell. In RNA virus infections, inclusions are most commonly found in the cytoplasm, whereas in DNA virus infections they are found in the nucleus.

Viral culture can help establish the diagnosis, but it also has limitations because viral cultures are usually identified only after 10–15 days, and the result depends on proper sample collection and timely transportation to the laboratory. Serological tests may also be performed to confirm the diagnosis.

Changes observed on chest X-ray are not specific, but certain findings may raise suspicion of a viral infection and help differentiate it from a bacterial infection (Table 2).

Table 2. Radiographic Findings on Chest X-Ray Suggestive of Viral or Bacterial Pneumonia

Principles of Treatment

Viral pneumonia can often be treated on an outpatient basis. The main goal of treatment is symptom relief. In addition to symptomatic treatment, specific therapy is available for some types of viral pneumonia. Ribavirin is prescribed for pneumonia caused by RSV, parainfluenza virus, adenovirus, and measles virus, while acyclovir is used for pneumonia caused by herpes simplex virus and varicella-zoster virus. Ganciclovir is recommended for cytomegalovirus-induced pneumonia, while oseltamivir, peramivir, and zanamivir can be used for influenza-induced pneumonia (9).

Although the course of viral pneumonia is often uncomplicated, severe cases can lead to sepsis, multiple organ failure, and acute respiratory failure. Severe pneumonia not only increases the need for hospitalization but may also require intensive care. The most important measures are to ensure adequate oxygenation and correct dehydration with intravenous fluids.

A study investigating the frequency of respiratory failure in patients with viral pneumonia found that respiratory failure develops in 20% of cases (12). Mortality among patients with viral pneumonia was similar to that among patients with bacterial pneumonia (12).

It is important to remember that bacterial pneumonia often accompanies viral pneumonia, and antibiotic treatment may therefore be necessary. A secondary bacterial infection can lead to abscess formation, empyema, or fluid accumulation in the pleural cavity.

Prevention

Protection against certain viral infections can be achieved through vaccination, including vaccination against measles, chickenpox, and influenza. After contact with a person infected with influenza, antiviral medications may be used for prophylaxis.

It is important to educate and monitor patients with compromised immune systems, including patients undergoing chemotherapy or radiation therapy and those taking immunosuppressive medications.

Depending on the virulence of the pathogen, the patient's age, and underlying diseases, viral pneumonia can range from a mild illness to a life-threatening condition. Therefore, adequate treatment and prevention are essential.

Publication "Internist," No. 8, 2018.

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