Treatment
Site of Care Decision
For patients with CAP, the clinician must decide whether the patient will be treated in an outpatient or inpatient setting, and for those in the inpatient setting, whether they can safely be treated on the general medical ward or should be the ICU. Two common scoring systems that can be used to aid the clinician in determining severity of the infection and guiding site-of-care decisions are the Pneumonia Severity Index (PSI) and CURB-65 scores.
The PSI score uses 20 different parameters, including comorbidities, laboratory parameters and radiographic findings to stratify patients into 5 mortality risk classes [35]. On the basis of associated mortality rates, it has been suggested that risk class I and II patients should be treated as outpatients, risk class III patients should be treated in an observation unit or with a short hospitalization, and risk class IV and V patients should be treated as inpatients [35].
The CURB-65 method of risk stratification is based on 5 clinical parameters: confusion, urea level, respiratory rate, systolic blood pressure and age ≥ 65 (Table 3) [36].
Patients with CURB-65 scores of 4 or 5 are considered to have severe pneumonia and admission to the ICU should be considered. Aside from the CURB-65 score, anyone requiring vasopressor support or mechanical ventilation merits admission to the ICU [16]. IDSA/ATS guidelines also recommend the use of “minor criteria” for making ICU admission decisions; these include respiratory rate ≥ 30 breaths / minute, PaO2 fraction ≤ 250, multilobar infiltrates, confusion, blood urea nitrogen ≥ 20 mg/dL, leukopenia, thrombocytopenia, hypothermia and hypotension [16]. These factors are associated with increased mortality due to CAP and admission to an ICU is indicated if 3 of the minor criteria for severe CAP are present.
Similar to CURB-65, another clinical calculator that can be used for assessing severity of CAP is SMART-COP [39]. This scoring system uses 8 weighted criteria to predict which patients will require intensive respiratory or vasopressor support. SMART-COP has a sensitivity of 79% and specificity 64% in predicting ICU admission, whereas CURB-65 had a pooled sensitivity of 57.2% and specificity of 77.2% [40].
Antibiotic Therapy
Antibiotics are the mainstay of treatment for CAP, with the majority of patients with CAP treated empirically taking into account the site of care, likely pathogen, and antimicrobial resistance issues. Patients with pneumonia who are treated as outpatients usually respond well to empiric antibiotic treatment and a causative pathogen is not usually sought. Patients who are hospitalized for treatment of CAP usually receive empiric antibiotic on admission. Once the etiology has been determined by microbiologic or serologic means, antimicrobial therapy should be adjusted accordingly. As noted previously, a CDC study found that the burden of viral etiologies was higher than previously thought, with rhinovirus and influenza accounting for 15% of cases and S. pneumoniae for only 5% [9]. This study highlighted the fact that despite advances in molecular techniques, most patients with pneumonia have no pathogen identified [9]. Given the lack of discernable pathogens in the majority of cases, unless a nonbacterial etiology is found patients should continue to be treated with antibiotics.
Outpatients without comorbidities or risk factors for drug-resistant S. pneumoniae (Table 4)
As previously mentioned, antibiotic therapy is typically empiric; neither clinical features nor radiographic features are sufficient to include or exclude infectious etiologies. Epidemiologic risk factors should be considered and, in certain cases, expanded antimicrobial coverage to include those entities; for example, treatment of anaerobes in the setting of lung abscess and antipseudomonal antibiotics for patients with bronchiectasis.
Of concern in the treatment of CAP is the increased prevalence of antimicrobial resistance among S. pneumoniae. The IDSA guidelines report that drug-resistant S. pneumoniae is more common in persons aged < 2 or > 65 years, and those with ß-lactam therapy within the previous 3 months, alcoholism, medical comorbidities, immunosuppressive illness or therapy, or exposure to a child who attends a day care center [16].
S. aureus should be considered during influenza outbreaks, with either vancomycin or linezolid being the recommended agents in the setting of methicillin-resistant S. aureus (MRSA). In a study comparing vancomycin versus linezolid for nosocomial pneumonia, the all-cause 60-day mortality was similar for both agents [41]. Datpomycin is another agent used against MRSA; however, its use in the setting of pneumonia is not indicated as daptomycin binds to surfactant, yielding it ineffective in the treatment of pneumonia [42]. Ceftaroline is a newer cephalosporin with activity against MRSA; its role in treatment of community-acquired MRSA pneumonia has not been fully elucidated, but it appears to be a useful agent for this indication [43,44].
A summary of recommended empiric antibiotic therapy is presented in Table 5.
Antibiotic Therapy for Selected Pathogens
S. pneumoniae
Patients with pneumococcal pneumonia who have penicillin-susceptible strains can be treated with intravenous penicillin (2 or 3 million units every 4 hours) or ceftriaxone. Once a patient meets criteria of stability, they can then be transitioned to oral penicillin, amoxicillin, or clarithromycin. Those with strains with reduced susceptibility can still be treated with penicillin but at a higher dose (4 million units IV every 4 hours) or a third-generation cephalosporin. Those whose pneumococcal pneumonia is complicated by bacteremia will benefit from dual therapy if severely ill, requiring ICU monitoring. Those not severely ill can be treated with monotherapy [46].
S. aureus
S. aureus is more commonly associated with hospital-acquired pneumonia but may also be seen during the influenza season and in those with severe necrotizing CAP. Both linezolid and vancomycin can be used to treat MRSA CAP. As noted above, ceftaroline has activity against MRSA and is approved for treatment of CAP, but is not approved by the FDA for MRSA CAP treatment. Similarly, tigecycline is approved for CAP and has activity against MRSA, but is not approved for MRSA CAP. Moreover, the FDA has warned of increased risk of death with tigecycline and has a black box warning to that effect [47].
Legionella
Treatment of legionellosis can be achieved with tetracyclines, macrolides, or fluoroquinolones. For nonimmunosuppressed patients with mild pneumonia, any of the listed antibiotics is considered appropriate. However, patients with severe infection or those with immunosuppression should be treated with either levofloxacin or azithromycin for 7 to 10 days [48].