INTRODUCTION AND EPIDEMIOLOGY
The student will be able to identify the most common viral, atypical, and bacterial lung infections in pediatric patients.
The student will be able to differentiate among the epidemiologies of infections caused by these organisms, and the underlying pathophysiology of disease.
The student will be able to describe the clinical signs and symptoms associated with pneumonia and lower respiratory tract infections in children.
The student will be able to outline the potential complications arising from bacterial pneumonias among pediatric patients.
Respiratory infections in children, particularly community-acquired bacterial pneumonias, are among the most important worldwide public health issues. Pneumonia is the most common cause of death in children <5 years of age and is particularly important in developing countries. It is estimated that 4-5 million children die annually of bacterial pneumonias, with the large majority of those deaths occurring in developing countries. In the United States, about 6 in 1,000 children over the age of 9 years develop pneumonia, while the incidence in children <5 years old is more than 5 times this rate. In less affluent countries, the incidence of pneumonia is an order of greater magnitude, primarily owing to other factors including malnutrition, environmental and indoor air pollution, immunization status, crowding, and coinfection with HIV or measles. Although bacterial pneumonias are an important cause of morbidity and mortality throughout the world, nonbacterial pneumonias and viral lower respiratory tract infections (such as bronchiolitis) are more prevalent in newborns and children. Terms such as viral pneumonia, atypical pneumonia, and interstitial pneumonia are used to describe the clinical presentations and radiographic images of patients presenting with these latter illnesses. This chapter addresses respiratory infections—both "atypical" and bacterial—in newborns and children.
Etiology and Age-Specific Considerations
In determining the possible etiology of pneumonia in a specific child, it is useful to appreciate that certain infectious causes are more or less unique to particular age groups. The most important of these by age cohort are shown in Table 40.1. In the first month of life, most cases of pneumonia are caused by either group B Streptococcus or gram-negative pathogens such as E. coli. This chapter will not specifically review pneumonias in neonates, but instead will focus on children beyond the newborn period. Viruses as a group are the most common causes of pneumonia in younger children. The specific viral pathogens causing such pneumonia, as well as their relative frequencies and usual severities, are depicted in Table 40.2.
Table 40.1Lower respiratory tract pathogens in relation to age groupa |Favorite Table|Download (.pdf) Table 40.1 Lower respiratory tract pathogens in relation to age groupa
|Age Cohort ||Pathogens in Order of Frequency Encountered |
|Neonates (<1 month) ||Group B Streptococci; E. coli; other gram-negative bacteria; S. pneumoniae; Haemophilus influenzae (type B and nontypable). |
|1-3 months: febrile ||Respiratory syncytial virus (RSV); other viruses (parainfluenza, influenza, adenovirus); S. pneumoniae; H. influenza (type B and nontypeable). |
|1-3 months: afebrile ||Chlamydia trachomatis, Mycoplasma hominis, Ureaplasma urealyticum, cytomegalovirus (CMV). |
|3-12 months ||RSV; other viruses (parainfluenza, influenza, adenovirus); S. pneumoniae; H. influenza (type B and nontypeable); C. trachomatis; Mycoplasma pneumonia; Group A Streptococcus. |
|2-5 years ||Respiratory viruses (parainfluenza, influenza, adenovirus); S. pneumonia; H. influenza (type B and nontypeable); M. pneumonia; Chlamydia pneumoniae; Staphylococcus aureus; group A Streptococcus. |
|5-18 years ||M. pneumonia; S. pneumoniae; C. pneumonia; H. influenzae (type B and nontypeable); influenza viruses; adenoviruses; other respiratory viruses. |
Table 40.2Most common viral and atypical pathogens by age group