Management of community-acquired pneumonia (CAP)

The most common bacterial causes of community-acquired pneumonia (CAP) in outpatients are Streptococcus pneumoniae, Haemophilus...

Assessment

The need for hospitalization should be based on clinical judgment plus results of a validated prognostic tool. Use of the pneumonia severity index (PSI) is recommended over CURB-65. PSI is better than the CURB-65 at identifying patients who can safely be treated as outpatients, but CURB-65 is easier to use.

PSI may underestimate severity in younger patients.

The PSI is available at https://www.mdcalc.com/psi-port-score-pneumonia-severity-index-cap and the CURB-65 is available at https://www.mdcalc.com/curb-65-score-pneumonia-severity.

Patients with severe pneumonia are typically those requiring intensive/critical care. For further information, see ATS/IDSA guideline criteria for severe pneumonia. Patients with community-acquired pneumonia (CAP) should be treated with antibiotics for at least five days (7 days for MRSA or Pseudomonas). Antibiotics should not be stopped until the patient is clinically stable. This means abnormalities in vitals (heart rate, blood pressure, respiratory rate, oxygen saturation, and body temperature) and cognition have resolved, and the patient is eating.

The most common bacterial causes of community-acquired pneumonia (CAP) in outpatients are Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae, Staphylococcus aureus, Legionella species, Chlamydia pneumoniae, and Moraxella cararhalis. It is suggested that anaerobic coverage not be routinely added in cases of aspiration pneumonia unless lung abscess or empyema is suspected. Blood culture yield is low in patients with non-severe CAP. Blood cultures are not recommended in outpatients, and it is suggested that they not be routinely done in the hospital setting in non-severe CAP. Blood cultures are recommended in severe CAP, and in patients being treated empirically for, or previously infected with, Pseudomonas aeruginosa or MRSA, or who had been hospitalized and received parenteral antibiotics within the prior 90 days.

Lab tests

Sputum gram stain and culture is recommended in severe CAP, in patients being treated empirically for, or previously infected with, Pseudomonas aeruginosa or MRSA, and perhaps in those hospitalized and treated with antibiotics within the prior 90 days. Collection of lower respiratory tract secretions for Legionella culture or nucleic acid amplification testing is suggested in severe CAP. Urine antigen testing for Pneumococcus and Legionella is suggested in severe CAP. Legionella testing is also suggested if epidemiology indicates exposure (e.g. travel in the previous ten days; outbreak). If influenza is circulating in the community, testing with a rapid molecular assay (preferred over an antigen test) is suggested. Coverage for influenza is suggested for outpatients who test positive, and is recommended for inpatients who test positive. Procalcitonin is not recommended to determine need for initial, empiric antibiotic treatment. Empiric antibiotics should be started if CAP is clinically suspected and radiographically confirmed, regardless of procalcitonin level; new evidence suggests that sensitivity is inadequate to determine when initial antibiotic therapy can be safely deferred in this setting.

Management

Role of corticosteroids

Guidelines suggest not using corticosteroids routinely for severe CAP. Corticosteroids can be considered in refractory septic shock, and of course for steroid-responsive comorbidities (e.g. COPD, asthma, autoimmune disease, etc). Corticosteroids may reduce mortality in severe CAP (NNT = 18), although mortality benefit is not consistent across studies. Corticosteroids may reduce time to clinical stability and length of stay by about one day, and reduce the need for mechanical ventilation. More study is needed to identify which subgroups benefit the most (e.g. patients with high inflammatory response). Consider corticosteroids for patients who are clinically unstable or not responding to treatment, and perhaps those with baseline C-reactive protein.

Outpatient antibiotic regimen

I- Without risk factors

For previously healthy without comorbidities (see below) and without risk factors for Pseudomonas aeruginosa or MRSA (e.g. prior respiratory isolation of MRSA or Pseudomonas aeruginosa, or hospitalization and receipt of parenteral antibiotics within the 90 days prior), consider amoxicillin/clavulanate 1 g TID (high dose targets resistant Streptococcus pneumoniae). OR macrolide (if local pneumococcal resistance is < 25%) such as azithromycin 500 mg x 1, then 250 mg once daily, or clarithromycin 500 mg BID or 1000 mg once daily (extended-release). OR, doxycycline 100 mg BID (consider a loading dose of 200 mg).

Note! Patients with risk factors for MRSA or Pseudomonas are not commonly managed as outpatients, but if they are, they will need coverage for these pathogens as well.

II- With comotbidities

For patients with heart disease, lung disease, liver disease, kidney disease, diabetes, alcoholism, cancer, asplenia, the regimens should target resistant Streptococcus pneumoniae, atypicals, beta-lactamase-producing Haemophilus influenzae and Moraxella catarrhalis, enteric gram negatives, and methicillin-susceptible Staphylococcus aureus. Consider amoxicillin/clavulanate (500 mg/125 mg TID or 875 mg/125 mg BID, 2,000 mg/125 mg BID) or cephalosporin (cefpodoxime 200 mg BID or cefuroxime 500 mg BID) PLUS doxycycline 100 mg BID (consider a loading dose of 200 mg) or macrolide such as azithromycin 500 mg x 1, then 250 mg once daily, or clarithromycin 500 mg BID or 1,000 mg once daily (extended-release). Monotherapy with a respiratory quinolone, levofloxacin 750 mg once daily, moxifloxacin 400 mg once daily, gemifloxacin 320 mg once daily, delafloxacin 450 mg orally every 12 h.

Inpatient antibiotic regimen

I- Without risk factors

Non-severe pneumonia without risk factors for Pseudomonas aeruginosa or MRSA, consider ampicillin/sulbactam (1.5 to 3 g every 6 h), or cephalosporin (cefotaxime 1 to 2 g every 8 h, ceftriaxone 1 to 2 g once daily, or ceftaroline 600 mg every 12 h) PLUS doxycycline 100 mg BID or macrolide such as azithromycin 500 mg once daily, or clarithromycin 500 mg BID. Monotherapy with a respiratory quinolone, levofloxacin 750 mg once daily, moxifloxacin 400 mg once daily, or delafloxacin 300 mg IV every 12 h. Evidence favors beta-lactam/macrolide combination.

II- With risk factors

Severe pneumonia without risk factors for Pseudomonas aeruginosa or MRSA, consider beta-lactam plus a macrolide, or a beta-lactam plus a respiratory quinolone. Dosing as above. For severe pneumonia, add MRSA coverage to above inpatient regimen and use cultures/nasal PCR to guide need for continuation/discontinuation of MRSA coverage. For non-severe, add MRSA coverage to above inpatient regimen only if cultures or PCR are positive.

MRSA coverage by linezolid 600 mg BID, or vancomycin 15 mg/kg every 12 h with dose adjusted per levels.

If prior respiratory isolation of Pseudomonas aeruginosa, or hospitalization and parenteral antibiotics within 90 days prior and locally validated risk factors for Pseudomonas aeruginosa, change beta-lactam in above inpatient regimen to one with pseudomonal coverage, and use cultures/nasal PCR to guide need for continuation/discontinuation of pseudomonal coverage.

Pseudomonal coverage by piperacillin/tazobactam 4.5 g every 6 h, cefepime 2 g every 8 h, ceftazidime 2 g every 8 h, imipenem 500 mg every 6 h, meropenem 1 g every 8 h, aztreonam 2 g every 8 h.

References

Metlay JP, Waterer GW, Long AC, et al. Diagnosis and Treatment of Adults with Community-acquired Pneumonia. An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America. Am J Respir Crit Care Med. 2019;200(7):e45-e67.
Mandell LA, Wunderink RG, et al. Infectious Diseases Society of America/American Thoracic Society consensus guidelines on the management of community-acquired pneumonia in adults. Clin Infect Dis. 2007;44 Suppl 2(Suppl 2):S27-S72.
Briel M, Spoorenberg SMC, Snijders D, et al. Corticosteroids in Patients Hospitalized With Community-Acquired Pneumonia: Systematic Review and Individual Patient Data Metaanalysis. Clin Infect Dis. 2018;66(3):346-354.