Pneumonia

Whereas viruses are relatively uncommon causes of pneumonia in immunocompetent adults, they are very important in young children. RSV (Figs. 36-2A and 36-3A) and parainfluenza virus (mainly type 3) are between them responsible for 25% of all pneumonitis in infants in the first year of life. Influenza also causes a considerable number of deaths during epidemic years. Infections with adenoviruses 3 and 7 (Fig. 36-2B) are less common but can be severe, and long-term sequelae such as obliterative bronchiolitis or bronchiectasis may permanently impair lung function. Up lo 20% of pneumonitis in infants has been ascribed to perinatal infection with cytomegalovirus (see Chapter 20). CMV may also cause potentially lethal pneumonia in immu-

Fig. 36-2 Viral infections of the lung. Sections from fatal cases of pneumonitis in children, stained with hematoxylin and eosin (A) Respiratory syncytial virus bronchiolitis (magnification xl35) Note multinucleated giant cells being shed into a bronchiole which is surrounded by leukocytes (B) Adenovirus, pneumonia (magnification xJ26) Note characteristic intranuclear inclusions (C) Measles giant cell pneumonia (magnification. x216) Note multinucleated giant cell with intranuclear inclusions (Courtesy Drs I Jack and A Williams)

Fig. 36-2 Viral infections of the lung. Sections from fatal cases of pneumonitis in children, stained with hematoxylin and eosin (A) Respiratory syncytial virus bronchiolitis (magnification xl35) Note multinucleated giant cells being shed into a bronchiole which is surrounded by leukocytes (B) Adenovirus, pneumonia (magnification xJ26) Note characteristic intranuclear inclusions (C) Measles giant cell pneumonia (magnification. x216) Note multinucleated giant cell with intranuclear inclusions (Courtesy Drs I Jack and A Williams)

Fig. 36-3 Radiographs of viral pneumonitis Note streaky, patchy, or nodular consolidation only (A) Respiratory syncytial virus (B) Varicella (C, D) Influenza (Courtesy Dr J Forbes.)

nocompromised patients, as may measles (Fig. 36-2C), varicella, and adenoviruses. Moreover, viral pneumonia not uncommonly develops in adults with varicella (Fig. 36-3B), and in military recruits involved in outbreaks of adenovirus 4 or 7, whereas measles is quite often complicated by bacterial pneumonia, especially in malnourished children in Africa and South America. In the elderly, particularly in those with underlying pulmonary or cardiac conditions, influenza is a major cause of death, either via influenza pneumonitis (Fig. 36-3C,D) or, more commonly, via secondary bacterial pneumonia attributable to Staphylococcus aureus, Streptococcus pneumoniae, or Haemophilus influenzae.

Viral pneumonitis often develops insidiously following URTI, and the clinical picture may be atypical The patient is generally febrile, with a cough and a degree of dyspnea, and auscultation may reveal some wheezing or moist rales. Unlike typical bacterial lobar pneumonia with Tts uniform consolidation, or bronchopneumonia with its streaky consolidation, viral pneumonitis is usually confined to diffuse interstitial lesions. The radiologic findings are not striking; they often show little more than an increase in hilar shadows or, at most, scattered areas of consolidation (Fig. 36-3).

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