The first step in management of CAP is prevention. Vaccines against three common CAP pathogens are available: influenza, Streptococcus pneumonia (pneumococcus), and Haemophilus influenzae. Seasonal influenza vaccination is recommended for children who are 6-23 months old, adults > 50 years of age, healthcare providers, and certain other high-risk individuals including those with significant medical comorbidities. Likewise, pneumococcal vaccination is recommended for adults ≥65 years of age and for certain other high risk individuals, again including those with significant medical comorbidities.
Evaluation of a patient with suspected CAP starts with a comprehensive history including the presence or absence of fever, chills, malaise, cough, sputum production, dyspnea, and chest pain among other symptoms. Physical findings compatible with pneumonia include tachypnea, increased tactile fremitus, dullness to percussion, and inspiratory crackles or egophony on chest auscultation (Chap. 14). Opacities or parenchymal consolidation on thoracic imaging studies support the clinical diagnosis (Figs. 35.1, 35.2; see also Chap. 15).
Chest radiograph of a 53-year-old male patient with severe community-acquired pneumonia and acute respiratory failure demonstrating bilateral patchy airspace opacities, greater on the right side.
Chest CT scan of the same patient depicted in Fig. 35.1 at the mid-chest level demonstrating bilateral patchy air space opacities in a patient with CAP. Air bronchograms are notable on the patient's right side. Small bilateral pleural effusions are also present.
Because CAP by definition involves patients who develop pneumonia outside of a health care setting, one of the first steps in management is to decide the most optimal setting to provide safe treatment for the patient. For example, will outpatient treatment suffice, or does the patient need to be admitted to the hospital and if so, is intensive care unit (ICU) admission warranted? These questions are best answered by the initial assessment of severity of a patient's pneumonia. In this regard, a helpful tool is the CURB-65 score which is a refinement of an instrument originally set forth by the British Thoracic Society. CURB-65 is an acronym for the five components of the score: Confusion, Blood urea nitrogen level, Respiratory rate, Blood pressure, and age of 65 years or older (Table 35.1).
Table 35.1Computing a patient's CURB-65 score ||Download (.pdf) Table 35.1 Computing a patient's CURB-65 score
|Clinical Factor ||Points |
|Confusion ||1 |
|Blood urea nitrogen >19 mg/dL ||1 |
|Respiratory rate >30 breaths/min ||1 |
|Systolic blood pressure <90 mm Hg or diastolic blood pressure <60 mm Hg ||1 |
|Age ≥65 years ||+ 1 |
|Maximal total points ||5 |
The risk of mortality increases with increasing values of a CURB-65 score. Thus, patients with a CURB-65 score of 0 or 1 are considered at low risk for complications and can be usually considered for ambulatory treatment. In this context, however, other clinical factors such as the patient's living environment and social support, as well as comorbidities need to be taken into account to assure the safety and efficacy of treatment. Admission to the hospital is recommended when the patient's CURB-65 score is ≥2 and many patients with scores of ≥3 will require admission to the ICU. The American Thoracic Society (ATS) and Infectious Disease Society of America (IDSA) have also developed consensus-related criteria for Severe CAP (Table 35.2). By these criteria, patients with ≥ one major criteria or ≥ three minor criteria require ICU admission.
Table 35.2Criteria for severe community-acquired pneumonia ||Download (.pdf) Table 35.2 Criteria for severe community-acquired pneumonia
|Major Criteria |
|Invasive mechanical ventilation |
|Septic shock with the need for vasopressors |
|Minor Criteria |
|Respiratory rate ≥30 breaths/min |
|Pao2/FIo2 ratio ≤250 (see Chap. 28) |
|Multilobar infiltrates on chest imaging |
|Uremia (blood urea nitrogen level ≥20 mg/dL) |
|Leukopenia (white blood cell count <4000/μL) |
|Thrombocytopenia (platelet count <100,000/μL) |
|Hypothermia (core temperature <36°C) |
|Hypotension requiring aggressive fluid resuscitation |
Diagnostic tests to determine the specific organism responsible for the patient's CAP who will be treated as out-patients are optional. These tests include blood cultures, sputum Gram stain and culture, and urinary antigen tests for Legionella spp. and S. pneumonia (Chap. 19). Patients with a history of unusual environmental exposures, international travel within the past 2 weeks, pleural effusion, and severe underlying comorbidities such as active alcohol abuse, chronic liver disease, chronic obstructive lung disease, and asplenia, represent subpopulations in which such further testing for a specific organism is indicated. For patients with CAP who are admitted to the hospital, pretreatment blood cultures and sputum Gram stain and cultures are indicated if the patient has severe CAP or comorbidities. Patients requiring endotracheal intubation should have specimens obtained from the lower respiratory tract in the form of endotracheal aspirates or bronchoalveolar lavage (Chap. 18).
The choice of initial antibiotic(s) in CAP is guided by the anticipated susceptibility of the most likely pathogens. In some cases a pathogen will be identified via sputum smears, cultures, serologic or other diagnostic tests. Unfortunately, such results are rarely available when treatment needs to be initiated. At best, the identity of a pathogen is known within the first 24 hours, although the identification process usually takes longer. In many instances, a pathogen will never be identified. Clinically, the likely pathogens are determined by both the severity of the pneumonia and the specific comorbidities of the patient (Table 35.3). Across all severities of CAP, Streptococcus pneumoniae is the most commonly identified pathogen, whereas Mycoplasma pneumoniae, Chlamydia pneumoniae, and respiratory viruses are more common pathogens in patients who are less severely ill. In contrast, Staphylococcus aureus, Legionella spp., and gram-negative bacilli are more often found in patients with severe pneumonia. Specific comorbidities and the likely pathogens in CAP are shown in Table 35.4. Less common pathogens and associated clinical scenarios are listed in Table 35.5.
Table 35.3Most common causes of community-acquired pneumonia ||Download (.pdf) Table 35.3 Most common causes of community-acquired pneumonia
|Patient Type ||Etiology |
|Outpatient || |
|Inpatient (non-ICU) || |
Aspiration (of mixed oropharyngeal flora)
|Inpatient (ICU) || |
Table 35.4Risk factors for multidrug resistant pathogens causing HAP ||Download (.pdf) Table 35.4 Risk factors for multidrug resistant pathogens causing HAP
|Antimicrobial therapy in preceding 90 days |
|Current hospitalization of ≥5 days or more |
|High frequency of antibiotic resistance in the community or specific hospital unit |
|Risk factors for healthcare-related pneumonia |
| Hospitalization for 2 days or more in the preceding 90 days |
| Residence in nursing home or extended care facility |
| Home infusion therapy (including antibiotics) |
| Home wound care |
| Family member with multidrug-resistant pathogen |
|Immunosuppressive disease and/or therapy |
Table 35.5Initial antibiotic therapy for early-onset HAP in patients without significant risk factors for MDR pathogens ||Download (.pdf) Table 35.5 Initial antibiotic therapy for early-onset HAP in patients without significant risk factors for MDR pathogens
Physician task forces within the ATS and IDSA have developed evidence-based guidelines which suggest that initial antibiotic therapy for CAP be based on both the severity of pneumonia and the individual patient's specific comorbidities. In subjects who are to be treated as outpatients, a macrolide antibiotic is preferred, unless the patient has significant comorbidities in which case a respiratory fluoroquinolone is recommended. A a-lactam antibiotic plus a macrolide may be used in place of a respiratory fluoroquinolone. If the severity of pneumonia requires inpatient treatment, the preferred therapy is either a respiratory fluoroquinolone or a combination of a β-lactam antibiotic and a macrolide. Finally, for the severity ill patient with CAP that requires ICU admission, a β-lactam antibiotic or ampicillin-sulbactam in addition to a respiratory fluoroquinolone or macrolide is recommended. If a specific pathogen is identified, the antimicrobial regimen is subsequently tailored to the antimicrobial sensitivity of that organism.
CLINICAL CORRELATION 35.1
Patients with CAP should be treated with antimicrobial therapy for a minimum of 5 days and should be afebrile for at least 48 hours prior to discontinuing antibiotics. A longer duration of treatment is indicated in patients who are not clinically stable after 5 days. If the patient initially required intravenous antibiotic therapy, then a switch to oral antibiotic treatment is generally done only when there is hemodynamic stability and clinical improvement. A failure to improve, or a deterioration of the patient's condition despite antimicrobial treatment, can occur for a variety of reasons. The clinician must consider both the possibility of infection by a pathogen resistant to the chosen antibiotics, and the spread of intrapulmonary infection beyond the lungs. Thus, development of a complicated parapneumonic effusion or frank empyema in the pleural space is a common cause of treatment failure (Chap. 29). In addition, the development de novo of superimposed pulmonary infections such as a ventilator-associated pneumonia can result in failure of a patient to clinically improve (Chap. 28). The stress of CAP on the patient's systemic inflammatory responses can also exacerbate underlying co-morbidities, or cause the development of other medical problems. Lastly, the clinician must consider whether the initial diagnosis of CAP was correct.