A lower respiratory tract infection (LRTI) is an infection below the level of the larynx and includes bronchitis, bronchiolitis, and pneumonia. LRTIs result from viral or bacterial invasion of lung parenchyma. Viral infections are diagnosed by the recognition of characteristic constellation of clinical signs and symptoms and treatment consists of supportive care measures (except for influenza, antivirals may be given). Bacterial LRTIs (in particular bacterial pneumonia) requires expedient, effective, and specific antimicrobial therapy. An appropriate treatment regimen for the patient with an LRTI can be established with the aid of a thorough medical history, physical examination, chest radiograph, knowledge of common bacterial pathogens, and results of properly collected cultures. This chapter will focus on pneumonia; see the special considerations section for information on bronchitis and bronchiolitis.
Pneumonia is inflammation of the lung with consolidation and is classified by the setting in which it develops (eg, community-acquired or hospital-acquired). The etiology of bacterial pneumonia varies in accordance with the type of pneumonia. Table 21-1 lists common bacterial pathogens associated with the various classifications of pneumonia. Viruses are a common cause of community-acquired pneumonia (CAP) in adults (often co-infecting with bacteria) and in children (65%). Viral pneumonia in children is frequently caused by respiratory syncytial, influenza or parainfluenza virus.
TABLE 21-1Etiology and Treatment of Pneumonia in Adults |Favorite Table|Download (.pdf) TABLE 21-1Etiology and Treatment of Pneumonia in Adults
|Clinical Setting ||Usual Pathogens ||Empirical Therapy |
|Outpatient/Community Acquired |
|Previously healthy ||S. pneumoniae, M. pneumoniae, H. influenzae, C. pneumoniae, M. catarrhalis ||Macrolide/azalide,a or tetracyclineb |
|Comorbidities (eg, diabetes, heart/lung/liver/renal disease, and/or alcoholism) || |
MDR S. pneumoniae
Oseltamivir or zanamivir if <48° from onset of symptoms
Fluoroquinolonec or β-lactamd + macrolidea
Regions with >25% rate of macrolide-resistant S. pneumoniae
|S. pneumoniae, gram-negative bacilli || |
Fluoroquinolonec or β-lactam + macrolidea/doxycycline
|Inpatient/Community Acquired |
|Non-ICU ||S. pneumoniae, H. influenzae, M. pneumoniae, C. pneumoniae, Legionella sp. ||Fluoroquinolonec or β-lactamd + macrolidea/doxycycline |
|ICU || |
S. pneumoniae, S. aureus, Legionella sp., gram-negative bacilli, H. influenzae
If P. aeruginosa suspected
If MRSA suspected
β-Lactam + macrolidea/fluoroquinolonec
Piperacillin/tazobactam or meropenem or cefepime + fluoroquinolonec/AMG/azithromycin; or β-lactam + AMG + azithromycin/respiratory fluoroquinolonec
Above + vancomycin or linezolid
Oseltamivir or zanamivir ± antibiotics for 2° infection
|Hospital Acquired or Ventilator Associated |
|No risk factors for MDR pathogens (single-agent Pseudomonal coverage) ||S. pneumoniae, H. influenzae, MSSA enteric gram-negative bacilli ||Piperacillin/tazobactam, cefepime, levofloxacin, imipenem or meropenem |
|Risk factors for MDR pathogen (dual-agent Pseudomonal coverage) or septic shock || |
P. aeruginosa, K. pneumoniae (ESBL), Acinetobacter sp.
If MRSA or Legionella sp. suspected
Antipseudomonal cephalosporine or antipseudomonal carbapenem or Antipseudomonal β-lactam/β-lactamase inhibitor + antipseudomonal fluoroquinolonec or AMGg
Above + ...