In acute respiratory infections, viral infections account for 90%, with the majority being upper respiratory tract infections, including the common cold, pharyngitis, laryngotracheobronchitis, bronchiolitis, infantile herpangina, and epidemic pleurodynia. Viruses causing pneumonia are less common, with the influenza virus being the most frequent, followed by parainfluenza virus, cytomegalovirus, adenovirus, rhinovirus, coronavirus, and certain enteroviruses such as Coxsackie and echovirus, as well as herpes simplex, varicella-zoster, rubella, measles, and other viruses. Infants and young children often develop pneumonia due to respiratory syncytial virus infection. Viral pneumonia mostly occurs in winter and spring, either sporadically or in outbreaks. Among non-bacterial pneumonias, viral infections account for about 25–50%, primarily affecting children, while adults are relatively less affected. In recent years, due to the widespread use of immunosuppressive drugs in cancer and organ transplantation, as well as the increasing incidence of AIDS, viruses such as herpes simplex, varicella-zoster, and cytomegalovirus have been causing severe pneumonia. Viral pneumonia is an airborne infection transmitted through person-to-person droplets, mainly resulting from the downward spread of upper respiratory tract viral infections, often accompanied by tracheobronchitis. Livestock such as horses and pigs sometimes carry certain epidemic influenza viruses, with occasional contact transmission. Fecal-oral transmission occurs with enteroviruses, while respiratory syncytial virus spreads through dust. In organ transplant cases, viruses can be transmitted through multiple blood transfusions or even donor organs. Hematogenously disseminated viral pneumonia is not accompanied by tracheobronchitis.

The infection begins in the upper respiratory tract, with extensive damage to the airway epithelium, ulceration of the mucous membrane, and the formation of a fibrin-coated membrane. The defensive function of the airway is compromised, making it susceptible to bacterial infections. In individuals with weakened immune status, fungal or protozoan infections, particularly Pneumocystis carinii, may also occur. Viral pneumonia caused by sexually transmitted diseases leads to interstitial pneumonia, with large mononuclear cell infiltration in the alveolar septa. Alveolar edema and the presence of a hyaline membrane containing plasma proteins and fibrin thicken the alveolar diffusion distance. The pneumonia can be focal or widely diffuse, sometimes progressing to consolidation. Viral inclusion bodies may be observed in alveolar cells and macrophages. Exudates are present in the bronchioles. After the lesions resolve, pulmonary fibrosis or even nodular calcification may remain.

bubble_chart Clinical Manifestations

The clinical manifestations of this disease are generally mild, similar to those of mycoplasma pneumonia. The onset is gradual, with symptoms such as headache, fatigue, fever, cough, and the production of small amounts of sticky sputum. Signs are often absent. Chest X-rays show patchy, flaky, or uniform shadows of pulmonary inflammation. The total white blood cell count may be normal, decreased, or slightly increased. The course of the disease typically lasts 1 to 2 weeks. In immunocompromised patients, viral pneumonia is often more severe, presenting with persistent high fever, palpitations, shortness of breath, cyanosis, extreme exhaustion, and may be accompanied by shock, heart failure, and azotemia. Due to interstitial and intra-alveolar edema, severe cases may develop acute respiratory distress syndrome. Physical examination may reveal moist rales. Chest X-rays show diffuse nodular infiltrates, predominantly in the lower two-thirds of both lung fields.

1. Medical History and Symptoms:

The onset is slow. In the initial stage [first stage], symptoms of upper respiratory tract infection such as dry throat, sore throat, sneezing, runny nose, fever, headache, poor appetite, and general body aches are common. If the lesion involves the lung parenchyma, symptoms such as cough (mostly paroxysmal dry cough), chest pain, and shortness of breath may occur. Special attention should be paid to whether there is immunodeficiency or immunosuppression during the medical history inquiry.

2. Physical Examination Findings:

Signs are often not obvious. Occasionally, fine crackles may be heard in the lower lung fields.

3. Auxiliary Examinations:

(1) Chest X-ray: Reticular shadows appear in both lungs, with thickened and blurred lung markings. In severe cases, diffuse nodular shadows may be seen in the middle and lower lung fields, while consolidation is rare.

(2) Blood tests: The white blood cell count is generally normal but may be slightly elevated or decreased. In cases of secondary bacterial infection, the white blood cell count and neutrophil count may increase.

(3) Etiological examination: Viral culture is difficult and not routinely performed. If a sputum smear from a pneumonia patient reveals only scattered bacteria and a large number of nucleated cells, or if no pathogenic bacteria are found, viral pneumonia should be suspected.

(4) Serological tests: A fourfold or greater increase in antibody titers between paired sera from the acute phase and the stage of convalescence, as detected by complement fixation test, neutralization test, or serum inhibition test, is diagnostic. In recent years, the detection of virus-specific IgM antibodies in serum has aided early diagnosis. Rapid viral-specific diagnosis can be performed using methods such as immunofluorescence, enzyme-linked immunosorbent assay (ELISA), enzyme-labeled histochemistry, and horseradish peroxidase-anti-horseradish peroxidase (PAP) methods.

1. General Treatment:

Keep warm, maintain airway patency, prevent water, electrolyte, and acid-base imbalances, and provide oxygen therapy if necessary.

2. Antiviral Drugs:

Amantadine 0.1g, twice daily for 3-5 days; Ribavirin, 10mg/kg, 2-3 times daily, orally or by injection; Isatis root, Astragalus Root, Lonicera, Dyers Woad, Forsythia, etc., have certain antiviral effects. Alpha-interferon and thymosin may also be used.

3. Administer appropriate antibiotic treatment for secondary bacterial infections.

bubble_chart Prevention

After viral infection, antibodies appear relatively late and play a minor role in controlling the infection. Interferon has a protective effect against viral infections in susceptible cells, preventing the progression of the disease and its spread. Cellular immunity plays a role in controlling certain viruses. For example, individuals with cellular immune deficiencies, such as those with leukemia or Hodgkin's disease, are highly susceptible to herpes and chickenpox viruses but not to other viruses. Currently, attenuated measles live vaccines have been widely administered to infants and young children in China, making measles extremely rare, and measles pneumonia even more so.

Passive immunization with human immunoglobulin provides some protection for susceptible patients, particularly against chickenpox and measles. Although specific immunization offers protection against common colds, adenoviruses, measles, and other viruses, it cannot completely prevent outbreaks.