Pediatric Lung Disease

Foundations

Although upper respiratory tract infections are more common, children frequently develop lower respiratory tract infections, most notably pneumonia and bronchiolitis. Bronchiolitis (see Chapter 163 – Pediatric Lower Airway Obstruction) is primarily seen in children younger than 2 years old and manifests as wheezing and congestion due to a viral infection. Pneumonia is an inflammation of the lung tissue that is most often due to an infection but occasionally may follow a noninfectious insult. The diagnosis of pneumonia is made by clinical signs and symptoms and is often aided by an abnormal chest radiograph demonstrating pulmonary infiltrates ( Fig. 164.1 ). The clinical presentation of pneumonia is variable, ranging from a mild illness to life-threatening disease. A specific organism may be suggested by clinical and radiographic findings, but determination of a precise causative agent is not always possible given the limitations of diagnostic testing, nor is it critical in an emergency setting, as initial treatment is empiric. Infection rates for pneumonia in children vary inversely with age, averaging 40/1000 in preschool-age children and decreasing gradually to 7/1000 in 12- to 15-year-olds. Most deaths from pneumonia result from bacterial infections.

The causative organisms vary with the age of the child. Overall, viral agents cause up to 90% of all pneumonias and are more common in younger children. Bacteria predominate in neonates but become less frequent in toddlers and older children. Outside the neonatal period, the incidence of bacterial agents is stable throughout different age groups. Chlamydia trachomatis is a unique cause of pneumonia in infants 3 to 19 weeks of age. Bordetella pertussis classically occurs in infants younger than 1 year but may occur in older children and adolescents. Mycoplasma pneumoniae is one of the most common causes of pneumonia among children older than 5 years but may also be seen in younger children. Chlamydophila (formerly Chlamydia ) pneumoniae is also seen more often in children older than 5 years but may cause infection in younger children.

Among bacteria, group B streptococci and gram-negative bacilli predominate in neonates. Although rare, Ureaplasma urealyticum and Listeria monocytogenes may cause illness in infants younger than 2 months. Streptococcus pneumoniae is the leading bacterial cause of pneumonia in all age groups beyond the newborn period, whereas Staphylococcus aureus and Haemophilus influenzae are less common causative agents. A vaccine against H. influenzae type b first became available in 1985, and incidence of disease has decreased markedly with widespread immunization of infants and young children. In 2010, the 13-valent pneumococcal vaccine (Prevnar 13, Wyeth Pharmaceuticals, NY) replaced the heptavalent pneumococcal conjugate vaccine Prevnar (Wyeth). Prevnar 13 is recommended for the primary series at 2, 4, and 6 months of age, with a fourth booster dose given at 12 to 15 months of age. Vaccination is highly efficacious, with 85% protection against serotype-specific cases of pneumococcal pneumonia, decrease in carriage rates of the included serotypes in daycare settings, and even some protection against viral pneumonia (possibly due to frequent concomitant infection of viral pneumonia with pneumococcal infection). ^{, ,}

Less common bacterial agents include group A streptococci, Neisseria meningitidis, and anaerobic bacteria (usually in the setting of aspiration pneumonia). Unusual causes of pneumonia include Pseudomonas aeruginosa, Legionella pneumophila, Pneumocystis jiroveci, and rickettsial infections. The incidence of Mycobacterium tuberculosis has been increasing in the United States, particularly in urban and low-income areas and among non-White racial or ethnic groups. Infants and adolescents are at highest risk in the United States. Respiratory syncytial virus (RSV) and parainfluenza are the most frequent viral agents in infants younger than 1 year. Viruses that may be responsible for neonatal pneumonia include rubella, cytomegalovirus (CMV), and herpes simplex virus. Other viral agents include influenza, adenovirus, rhinovirus, enterovirus, measles, varicella, and Epstein-Barr virus. In addition, immunocompromised hosts are susceptible to mixed and opportunistic infections, including bacterial, viral (CMV, varicella), protozoan ( P. jiroveci ), and fungal disease ( Coccidioidomycosis , etc.).

The lung is protected from infection by a variety of local and systemic immune mechanisms. Passively acquired maternal antibodies are important in protection against S. pneumoniae and H. influenzae infections during the first few months of life. Children with altered protective mechanisms are at increased risk for development of pneumonia; this includes children with congenital anatomic abnormalities (e.g., cleft palate, tracheoesophageal fistulas, pulmonary sequestration, congenital cystic adenomatoid malformation), immune deficiencies (e.g., congenital, acquired, medication induced), neurologic alterations that predispose to aspiration (e.g. coma, seizures, cerebral palsy, general anesthesia), and alterations in quality of secreted mucus (cystic fibrosis [CF]).

Bacterial pneumonia and mycoplasma infections are usually transmitted person to person by droplet aspiration. Asymptomatic upper airway colonization often occurs in children and may spread infection to other children. Much less commonly, bacterial pneumonia may result from hematogenous spread from a distant focus or during primary bacteremia. Viral agents that cause pneumonia proliferate in the upper respiratory tract and spread contiguously to involve the lower respiratory tract. Viruses such as varicella, CMV, herpes simplex, Epstein-Barr, measles, and rubella also may infect the lungs through hematogenous spread.

Clinical Features

Clinical symptoms and signs of pneumonia in pediatric patients vary with patient age, specific pathogen, and disease severity. Infants younger than 3 months of age generally have respiratory symptoms, such as tachypnea, cough, retractions, and grunting, but may show only nonlocalizing symptoms, such as isolated fever or hypothermia, vomiting, poor feeding, irritability, and lethargy. Toddlers with S. pneumoniae infection may have nonspecific symptoms, such as high fever and lethargy, without significant respiratory symptoms. In general, signs and symptoms in children become more specific with increasing age, although pneumonia may have only subtle manifestations in any child. Systemic symptoms include fever and chills, headache, rigors, and malaise. Symptoms of lower respiratory tract disease may include cough and wheezing. Pleural irritation often causes chest pain, but the child may also complain of pain in the abdomen or neck. Vomiting (often posttussive) and poor oral intake are common.

Key historical factors include birth and immunization history (particularly pneumococcal and H. influenzae type b vaccination), sickle cell status, history of previous pneumonia or frequent infections, and presence of underlying chronic disease. Children with known respiratory (e.g., bronchopulmonary dysplasia [BPD], CF) or cardiac disease tend to have more severe courses of illness; children with a primary or acquired immunodeficiency are also prone to more severe and fulminant disease from common, uncommon, and opportunistic pathogens.

The physical examination should begin with the general appearance and breathing pattern. A full set of vital signs, including oxygen saturation, should be obtained on arrival. Fever is often present but may be low grade or absent. Important findings include hydration status, perfusion, and level of alertness and interaction. Abnormal cardiovascular parameters may indicate dehydration or, rarely, shock. Tachypnea, although not universal, is the most sensitive indicator of pneumonia and may be the only manifestation in younger children. The World Health Organization (WHO) has published guidelines for the clinical diagnosis of pneumonia in developing countries and cites tachypnea and retractions as indicators of lower respiratory disease ( Table 164.1 ).

Other manifestations of lower airway disease include cough, wheezing, or signs of increased work of breathing: nasal flaring, retractions, grunting, and accessory muscle use. The characteristics of the cough may aid in the diagnosis; a staccato cough in an infant may indicate pneumonia caused by C. trachomatis or B. pertussis . The patient’s lungs should be auscultated, and findings may include rales, wheezing, or diminished breath sounds. Although these may be present in younger children, the findings are much less consistent and may be masked by poor inspiratory effort or noisy upper airway sounds. Pleural irritation can cause abdominal tenderness or meningismus, and pulmonary hyperinflation may cause downward displacement of the liver and spleen. Extrapulmonary exam findings may include rhinorrhea, pharyngitis, or exanthem with viral infections. Conjunctivitis can be seen with chlamydial pneumonia, whereas pharyngitis and exanthems are associated with M. pneumoniae.

Several complications of pneumonia may result from local and systemic effects of the infection, with the most common systemic complication being dehydration. Pleural effusion or empyema is usually associated with bacterial pathogens (notably S. pneumoniae, H. influenzae, and S. aureus ) but are occasionally seen with mycoplasma, viral, and tuberculosis pneumonia. Similarly, lung abscess, pneumatocele, and pneumothorax are local complications primarily seen with bacterial disease, particularly with S. aureus . Extensive pulmonary involvement, regardless of the causative agent, may lead to hypoxia, progressive respiratory deterioration, and multiple organ failure ( Fig. 164.2 ). Apnea in isolation without other symptoms can occur in infants younger than 3 months and is usually associated with viral (especially RSV), chlamydial, and pertussis infections. Additional infectious foci may develop from concomitant bacteremia (e.g., meningitis, epiglottitis, pericarditis, septic arthritis, soft tissue infections). Viral or bacterial pneumonia is rarely associated with meningitis, encephalitis, arthritis, rhabdomyolysis, and hemolytic uremic syndrome.

Differential Diagnoses

Unfortunately, no single finding can reliably differentiate pneumonia from other causes of respiratory distress in children. The major conditions to be differentiated in children with pneumonia include bacterial pneumonias, viral disease, other unusual infectious causes (mycobacterial, protozoal, fungal), and noninfectious pathologic conditions ( Box 164.1 ). Common infectious causes classically present with certain historical, clinical, and laboratory findings ( Table 164.2 ). However, the broad spectrum of illness for each condition makes a definitive diagnosis difficult for any individual patient, and no specific feature can reliably differentiate bacterial from nonbacterial pneumonia. Providers should consider a bacterial cause in a child with a temperature higher than 39°C (102.2°F), clinical toxicity, lobar infiltrate, or pleural effusions ( Fig. 164.3 ). Host factors, epidemiology, clinical presentation, and judicious use of diagnostic tests can establish a likely diagnosis and appropriate empiric management.