Community-Acquired Pneumonia
By David J. Karras, MD, FAAEM, FACEP
Community-acquired pneumonia (CAP) develops in more than 5 million individuals annually in the United States, one-fifth of whom are hospitalized. While the overall mortality of CAP is 1-5%, mortality among hospitalized patients reaches 12%, underscoring that CAP is a frequent cause of death. Emergency physicians play a critical role in the evaluation and treatment of CAP. Studies suggest that time-to-antibiotic-treatment is an important predictor of outcome for patients with pneumonia, and that the majority of patients remain on the antibiotic started in the emergency department (ED).1 As emergency physicians, we need to correctly determine which CAP patients require hospitalization, decide which antibiotic is most appropriate, and ensure that therapy is delivered promptly.
Estimates of the frequency of specific pathogens in CAP vary widely, depending on the population studied and the method of identifying the organism. The most common pathogens implicated in healthy individuals are Streptococcus pneumoniae, Mycoplasma pneumoniae, and viral organisms, each recovered in 15-40% of CAP cases. No specific organism is recovered in at least one-third of patients, and multiple pathogens are recovered in about 20% of cases.2 Somewhat less common causes of CAP in healthy individuals include Chlamydia pneumoniae and Legionella pneumophila, each responsible for roughly 10-20% of cases. Additional organisms responsible for CAP in smokers are Haemophilus influenzae and Moraxella catarrhalis. Staphylococcus aureus and gram-negative entero-pathogens are uncommon in healthy individuals but are considerations in patients with underlying medical problems.
Determining Disposition
The Pneumonia Patient Outcomes Research Team (PORT) study is a landmark in decision analysis and sets de facto criteria for determining whether inpatient therapy is appropriate for patients with CAP.3 The authors identified a group at very low risk of CAP-related mortality: adults 50 years of age and younger with no serious underlying illness, a normal mental status, and relatively normal vital signs (pulse < 125 bpm, respiratory rate < 30/min, systolic blood pressure at least 90 mmHg, and temperature 35-40º C). These class I patients had CAP-related mortality less than 0.5% and, concluded the authors, can be treated safely at home.
Patients not meeting class I criteria still may be appropriate for outpatient therapy, but calculating their CAP-related mortality requires use of a fairly complex algorithm and a point scoring system based on co-morbidities, laboratory results, and vital sign abnormalities. The algorithm is contained in the article and the calculations can be performed easily online or with any of several medical software packages.
The Pneumonia PORT study was validated carefully and is employed widely both by health care workers to make admission decisions and by insurers to determine, retrospectively, whether hospitalization was justified.
While it’s essential that emergency physicians be familiar with the system, it should be recognized that the
Pneumonia PORT criteria do not account for exceptional circumstances such as absence of follow-up care, inability to obtain medication, inadequate social support, and other too-common, real-world scenarios. Interestingly, while a low PaO2 enters into the mortality calculations for patients in higher-risk classes, the authors did not include a low pulse oximetry value as a vital sign abnormality. A patient could therefore meet class I criteria despite a dangerously low oxygen saturation. Given these limitations, the decision whether to admit a patient with CAP still requires that physicians look beyond the algorithm.
Antibiotic Resistance Patterns
Recommendations for antibiotic treatment of CAP in otherwise healthy patients focus largely on the drugs’ anti-pneumococcal efficacy. In this country, at least 35% of pneumococcal isolates are penicillin-resistant, about 8% are cephalosporin-resistant, and 10-20% are macrolide-resistant in vitro. Pneumococcal resistance to fluoroquinolones is quite low (about 1% nationally), but there are a few communities in which this rate is greater than 10%.4 With increasing fluoroquinolone use, the resistance rate inevitably will continue to grow.
While it’s tempting to base therapy on antibiotic resistance patterns, it is important to note that there appears to be no link between in vitro pneumococcal resistance and clinical outcomes in CAP.5 This is in contrast to many diseases, such as with meningococcus, in which there is a strong relationship between drug resistance and treatment failure. While some studies have detected higher mortality in CAP patients with drug-resistant pathogens, these differences have disappeared when the results were controlled for co-morbidities and disease severity. In vitro drug resistance, therefore, does not appear to be an overriding factor in choosing an empiric antibiotic regimen for patients with CAP.
Antibiotic Selection
The Infectious Diseases Society of America (IDSA) and the American Thoracic Society (ATS) regularly issue guidelines for the management of CAP based on presumptive etiology.6,7 The Sanford Guide to Antimicrobial Therapy is a convenient and widely used reference that addresses empiric CAP treatment, incorporating both the IDSA and ATS guidelines as well as the authors’ own expert opinions. Any of these sources is an excellent reference when selecting an antibiotic for patients with CAP.
Patients with CAP first should be stratified according to the presence of significant co-morbidities and the treatment setting—outpatient, general hospital floor, or intensive care unit. Some panels advise obtaining a sputum culture prior to initiating antibiotics, while others forgo this step. For hospitalized patients, most infectious disease specialists would expect that blood cultures be obtained and at least an attempt made at obtaining sputum cultures prior to initiating antibiotics, although not the risk of delaying therapy.For otherwise healthy patients with CAP who don’t require hospitalization, a macrolide antibiotic or doxycycline is recommended. Gastrointestinal side effects and the prolonged course of therapy may make doxycycline compliance problematic, and macrolides may be more cost-effective in the long run despite their higher initial cost. Fluoroquinolones (other than ciprofloxacin) also are acceptable for treating outpatients. Some experts, however, do not recommend the fluoroquinolones for uncomplicated patients, based on recommendations from the Centers for Disease Control and Prevention’s (CDC) Drug-Resistant Streptococcus pneumoniae Therapeutic Working Group.8 The CDC panel advises restricting fluoroquinolones to limit emergence of drug-resistant pneumococci, and suggests that this class of antibiotics be used only in patients who have failed other regimens, who are allergic to alternatives, or who have documented infections with highly resistant organisms That being said, the "respiratory fluoroquinolones" are widely used and highly effective for treating CAP in otherwise healthy patients.
More aggressive therapy may be warranted for outpatients with underlying medical problems, and some experts advise adding an oral beta-lactam if macrolides are chosen (or using a fluoroquinolone for monotherapy). Similarly, hospitalized patients with CAP can be treated with a macrolide plus a third-generation cephalosporin or a fluoroquinolone alone—although some advise adding a third-generation cephalosporin to the fluoroquinolone, as well. Ampicillin-sulbactam plus a macrolide or doxycycline also is acceptable for uncomplicated inpatients.9 While IV therapy is no more effective than oral therapy for a patient with a working gastrointestinal tract, most hospitalized patients will receive IV therapy, either out of tradition or to justify the need for hospitalization.
Finally, for critically ill inpatients, all expert groups advise a two-drug regimen with either a third-generation cephalosporin or ampicillin-sulbactam added to either a fluoroquinolone or macrolide. This provides enhanced activity also against gram-negative enteric pathogens as well as antibiotic-resistance pneumococcus.
References
1. Marrie TJ. Community-acquired pneumonia: Epidemiology, etiology, treatment. Infect Dis Clin North Am 1998;12:723-740.
2. Bartlett JG, et al. Current concepts: Community-acquired pneumonia. N Engl J Med 1995;333:1618-1624.
3. Fine MJ, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia. N Engl J Med 1997;336:243-250.
4. Ferraro MJ, et al. Prevalence of fluoroquinolone resistance amongst Streptococcus pneumoniae isolated in the United States during the winter of 2000-01. The 42nd Interscience Conference on Antimicrobial Agents and Chemotherapy, 2002. Abstract C2-650.
5. Bauer T, et al. Streptococcus pneumoniae in community-acquired pneumonia. How important is drug resistance? Med Clin North Am 2001;85:1367-1379.
6. Bartlett JG, et al. Practice guidelines for the management of community-acquired pneumonia in adults. Infectious Diseases Society of America. Clin Infect Dis 2000;31:347-382.
7. Niederman MS, et al. Guidelines for the management of adults with community-acquired pneumonia. Diagnosis, assessment of severity, antimicrobial therapy, and prevention. Am J Respir Crit Care Med 2001;163:1730-1754.
8. Heffelfinger JD, et al. Management of community-acquired pneumonia in the era of pneumococcal resistance: A report from the Drug-Resistant Streptococcus pneumoniae Therapeutic Working Group. Arch Intern Med 2000;160:1399-1408.
9. Halm EA, et al. Management of community-acquired pneumonia. N Engl J Med 2002;347:2039-2045.
Community-acquired pneumonia (CAP) develops in more than 5 million individuals annually in the United States, one-fifth of whom are hospitalized. While the overall mortality of CAP is 1-5%, mortality among hospitalized patients reaches 12%, underscoring that CAP is a frequent cause of death.
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