Community-Acquired Pneumonia

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Chapter 392 Community-Acquired Pneumonia

Epidemiology

Pneumonia—inflammation of the parenchyma of the lungs—is a substantial cause of morbidity and mortality in childhood throughout the world, rivaling diarrhea as a cause of death in developing countries (Fig. 392-1). With ≈158 million episodes of pneumonia per year, of which ≈154 million are occurring in developing countries, pneumonia is estimated to cause ≈3 million deaths, or an estimated 29% of all deaths, among children younger than 5 yr worldwide. The incidence of pneumonia is more than 10-fold higher (0.29 episodes versus 0.03 episodes), and the number of childhood-related deaths due to pneumonia ≈2000-fold higher, in developing than in developed countries (Table 392-1).

In the USA from 1939 to 1996, pneumonia mortality in children declined by 97%. It is hypothesized that this decline is attributable to the introduction of antibiotics, vaccines, and the expansion of medical insurance coverage for children. Haemophilus influenzae type b (Hib) (Chapter 186) was an important cause of bacterial pneumonia in young children but has become uncommon with the routine use of effective vaccines. The introduction of heptavalent pneumococcal conjugate vaccine and its impact on pneumococcal disease (Chapter 175) has reduced the overall incidence of pneumonia in infants and children in the USA by ≈30% in the 1st yr of life, ≈20% in the 2nd yr of life, and ≈10% in children >2 yr of age. In developing countries, the introduction of measles vaccine has greatly reduced the incidence of measles-related pneumonia deaths.

Etiology

Although most cases of pneumonia are caused by microorganisms, noninfectious causes include aspiration of food or gastric acid, foreign bodies, hydrocarbons, and lipoid substances, hypersensitivity reactions, and drug- or radiation-induced pneumonitis. The cause of pneumonia in an individual patient is often difficult to determine because direct culture of lung tissue is invasive and rarely performed. Cultures performed on specimens obtained from the upper respiratory tract or “sputum” often do not accurately reflect the cause of lower respiratory tract infection. With the use of state-of-the-art diagnostic testing, a bacterial or viral cause of pneumonia can be identified in 40-80% of children with community-acquired pneumonia. Streptococcus pneumoniae (pneumococcus) is the most common bacterial pathogen in children 3 wk to 4 yr of age, whereas Mycoplasma pneumoniae and Chlamydophila pneumoniae are the most frequent pathogens in children 5 yr and older. In addition to pneumococcus, other bacterial causes of pneumonia in previously healthy children in the USA include group A streptococcus (Streptococcus pyogenes) and Staphylococcus aureus (Chapter 174.1) (Table 392-2).

Table 392-2 CAUSES OF INFECTIOUS PNEUMONIA

BACTERIAL
Common
Streptococcus pneumoniae Consolidation, empyema
Group B streptococci Neonates
Group A streptococci Empyema
Mycoplasma pneumoniae* Adolescents; summer-fall epidemics
Chlamydophila pneumoniae* Adolescents
Chlamydia trachomatis Infants
Mixed anaerobes Aspiration pneumonia
Gram-negative enterics Nosocomial pneumonia
Uncommon
Haemophilus influenzae type b Unimmunized
Staphylococcus aureus Pneumatoceles, empyema; infants
Moraxella catarrhalis  
Neisseria meningitidis  
Francisella tularensis Animal, tick, fly contact; bioterrorism
Nocardia species Immunosuppressed persons
Chlamydophila psittaci* Bird contact (especially parakeets)
Yersinia pestis Plague; rat contact; bioterrorism
Legionella species* Exposure to contaminated water; nosocomial
Coxiella burnetii* Q fever; animal (goat, sheep, cattle) exposure
VIRAL
Common
Respiratory synctial virus Bronchiolitis
Parainfluenza types 1-3 Croup
Influenza A, B High fever; winter months
Adenovirus Can be severe; often occurs between January and April
Human metapneumovirus Similar to respiratory syncytial virus
Uncommon
Rhinovirus Rhinorrhea
Enterovirus Neonates
Herpes simplex Neonates
Cytomegalovirus Infants, immunosuppressed persons
Measles Rash, coryza, conjunctivitis
Varicella Adolescents or unimmunized
Hantavirus Southwestern USA, rodents
Coronavirus (severe acute respiratory syndrome) Asia
FUNGAL
Histoplasma capsulatum Ohio/Mississippi River valley; bird, bat contact
Blastomyces dermatitidis Ohio/Mississippi River valley
Coccidioides immitis Southwest USA
Cryptococcus neoformans Bird contact
Aspergillus species Immunosuppressed persons; nodular lung infection
Mucormycosis Immunosuppressed persons
Pneumocystis jiroveci Immunosuppressed, steroids
RICKETTSIAL  
Rickettsia rickettsiae Tick bite
MYCOBACTERIAL  
Mycobacterium tuberculosis Travel to endemic region; exposure to high-risk persons
Mycobacterium avium complex Immunosuppressed persons
PARASITIC  
Various parasites (e.g., Ascaris, Strongyloides species) Eosinophilic pneumonia

* Atypical pneumonia syndrome; may have extrapulmonary manifestations, low-grade fever, patchy diffuse infiltrates, poor response to beta-lactam antibiotics, and negative sputum Gram stain.

From Kliegman RM, Greenbaum LA, Lye PS: Practical strategies in pediatric diagnosis & therapy, ed 2, 2004, Philadelphia, Elsevier, p 29.

S. pneumoniae, H. influenzae, and S. aureus are the major causes of hospitalization and death from bacterial pneumonia among children in developing countries, although in children with HIV infection, Mycobacterium tuberculosis (Chapter 207), atypical mycobacteria, Salmonella (Chapter 190), Escherichia coli (Chapter 192), and Pneumocystis jiroveci (Chapter 236) must be considered. The incidence of H. influenzae has been significantly reduced in areas where routine Hib immunization has been implemented.

Viral pathogens are a prominent cause of lower respiratory tract infections in infants and children <5 yr of age. Viruses are responsible for 45% of the episodes of pneumonia identified in hospitalized children in Dallas. Unlike bronchiolitis, for which the peak incidence is in the 1st yr of life, the highest frequency of viral pneumonia occurs between the ages of 2 and 3 yr, decreasing slowly thereafter. Of the respiratory viruses, influenza virus (Chapter 250), and respiratory syncytial virus (RSV) (Chapter 252) are the major pathogens, especially in children <3 yr of age. Other common viruses causing pneumonia include parainfluenza viruses, adenoviruses, rhinoviruses, and human metapneumovirus. The age of the patient may help identify possible pathogens (Table 392-3).

Table 392-3 ETIOLOGIC AGENTS GROUPED BY AGE OF THE PATIENT

AGE GROUP FREQUENT PATHOGENS (IN ORDER OF FREQUENCY)
Neonates (<3 wk) Group B streptococcus, Escherichia coli, other gram-negative bacilli, Streptococcus pneumoniae, Haemophilus influenzae (type b,* nontypable)
3 wk-3 mo Respiratory syncytial virus, other respiratory viruses (parainfluenza viruses, influenza viruses, adenovirus), S. pneumoniae, H. influenzae (type b,* nontypable); if patient is afebrile, consider Chlamydia trachomatis
4 mo-4 yr Respiratory syncytial virus, other respiratory viruses (parainfluenza viruses, influenza viruses, adenovirus), S. pneumoniae, H. influenzae (type b,* nontypable), Mycoplasma pneumoniae, group A streptococcus
≥5 yr M. pneumoniae, S. pneumoniae, Chlamydophila pneumoniae, H. influenzae (type b,* nontypable), influenza viruses, adenovirus, other respiratory viruses, Legionella pneumophila

From Kliegman RM, Marcdante KJ, Jenson HJ, et al: Nelson essentials of pediatrics, ed 5, Philadelphia, 2006, Elsevier, p 504.

* H. influenzae type b is uncommon with routine H. influenzae type b immunization.

Lower respiratory tract viral infections in the USA are much more common in the fall and winter, in relation to the seasonal epidemics of respiratory viral infection that occur each year. The typical pattern of these epidemics usually begins in the fall, when parainfluenza infections appear and most often manifest as croup. Later in winter, RSV, human metapneumovirus, and influenza viruses cause widespread infection, including upper respiratory tract infections, bronchiolitis, and pneumonia. RSV attacks infants and young children, whereas influenza virus causes disease and excess hospitalization for acute respiratory illness in all age groups. Knowledge of the prevailing viral epidemic may lead to a presumptive initial diagnosis.

Immunization status is relevant because children fully immunized against H. influenzae type b and S. pneumoniae are less likely to be infected with these pathogens. Children who are immunosuppressed or who have an underlying illness may be at risk for specific pathogens, such as Pseudomonas spp. in patients with cystic fibrosis.