Pulmonary Medicine

Community-Acquired Pneumonia

What every physician needs to know:

Community acquired pneumonia (CAP), defined as an infection of the alveoli, the distal airways, and the lnterstitium of the lungs acquired while the patient is in the community, is associated with significant morbidity, mortality, and cost. Clinical stratification is important in assisting clinicians to admit the patient to the hospital or, if the patient is severely ill, to the Intensive Care Unit (ICU). Approximately 10 percent of patients who are hospitalized with CAP require ICU admission; the mortality rate ranges from 30 percent to 60 percent in this setting. Pneumonia is the eighth leading cause of death overall and the most common cause of death from infectious disease in the United States.

Classification:

Not applicable.

Are you sure your patient has community-acquired pneumonia? What should you expect to find?

The most common symptoms are fever, cough (nonproductive or productive of purulent sputum), pleuritic chest pain, dyspnea, chills, and rigors. Patients present less commonly with diarrhea, new-onset or worsening confusion in elderly patients, and headache.

Findings on physical examination of the chest include dullness to percussion, increased tactile and vocal fremitus, egophony, crackles, whispering pectoriloquy, and pleural friction rub. Tachypnea higher than 25/min alone or 20/min with associated tachycardia (>100/min) and fever increases the likelihood that pneumonia is present.

Beware: there are other diseases that can mimic community-acquired pneumonia:

Diseases that share similar clinical and radiographic features include pulmonary embolism, lung cancer, pulmonary hemorrhage, pulmonary edema, and inflammatory disorders (sarcoidosis, Wegener's, vasculitis, and other rheumatologic diseases, and bronchiolitis obliterans organizing pneumonia (BOOP)).

How and/or why did the patient develop community-acquired pneumonia?

Pneumonia is the product of proliferation of microbial pathogens and the host's response to them in the alveolar space. The most common mechanism for infection occurs when microorganisms gain access to the alveolar space after aspiration from the oropharynx. However, organisms can be inhaled as contaminated droplets or, less commonly, can be hematogenously spread.

Host barriers that must be overcome for the organism to initiate infection include the hairs and turbinates of the nares, the branching architecture of the tracheobronchial tree, mucocillary clearance, local antibacterial factors, the gag reflex, and cough. Alveolar macrophages are highly efficient in killing and clearing pathogens that, once engulfed, can be eliminated by mucocillary system or lymphathics; however, when the functionality of alveolar macrophages is exceeded, then pneumonia is manifested. The resultant clinical syndrome is mainly due to the activation of the host inflammatory response, rather than to proliferation of microorganisms.

Which individuals are at greatest risk of developing community-acquired pneumonia?

Pneumonia is more common among African Americans and men than among whites and women. Chronic obstructive pulmonary disease (COPD), alcoholism, chronic heart disease, and diabetes mellitus are the most common comorbidities associated in patients with CAP.

What laboratory studies should you order to help make the diagnosis, and how should you interpret the results?

In addition to sputum and blood cultures, several laboratory studies should be considered in the appropriate setting:

  • Serologic test initially and in the convalescent stages for Legionalla spp, M, pneumoniae, and C. pneumoniae, if no CRP is available for these pathogens

  • Urinary antigen for Legionella spp and Streptococcus pneumoniae

  • Direct rapid viral test of nasal swab by nucleic acid amplification for influenza, respiratory syncytial virus (RSV), adenovirus, parainfluenza, rhinovirus, and human metapneumovirus

  • Sputum stains for pneumocystis and acid fast bacilli

In addition, routine labs, including CBC, electrolytes, BUN/creatinine, and liver function studies, should be obtained in all patients. An arterial blood gas should be obtained in patients who exhibit signs of respiratory distress or altered mental status.

What imaging studies will be helpful in making or excluding the diagnosis of community-acquired pneumonia?

A chest x-ray (preferably PA and lateral) should be obtained in all patients suspected of having pneumonia. Findings include consolidation, interstitial infiltrates, and cavitation. Chest x-ray is also helpful in assessing for an associated parapneumonic effusion; in equivocal cases, a lateral decubitus film or ultrasound should be obtained.

If there is a high index of suspicion for pneumonia but the initial chest x-ray does not demonstrate an opacity, consideration should be given to repeating the film in 24 to 48 hours or obtaining a chest CT scan.

What non-invasive pulmonary diagnostic studies will be helpful in making or excluding the diagnosis of community-acquired pneumonia?

Not applicable

What diagnostic procedures will be helpful in making or excluding the diagnosis of community-acquired pneumonia?

Bronchoscopy should be considered to obtain lower respiratory samples for further studies in cases where the diagnosis remains in doubt, high-grade proximal bronchial obstruction is suspected (i.e., post-obstructive pneumonia), unusual pathogens are a consideration, or the patient is not responding appropriately to empiric antibiotic therapy.

if a pleural effusion is detected on chest x-ray and is confirmed to be greater than 1cm on lateral decubitus chest x-ray, thoracentesis should be performed to assess for the presence of empyema and the need for a chest tube.

What pathology/cytology/genetic studies will be helpful in making or excluding the diagnosis of community-acquired pneumonia?

Not applicable.

If you decide the patient has community-acquired pneumonia, how should the patient be managed?

The first decision that the clinician must make is whether the patient with CAP needs to be hospitalized and, if so, whether care should take place on the regular hospital floor or the ICU based on the severity of illness. Two important scoring systems for severity are the CURB-65 rule and American Thoracic Society (ATS) modified criteria.

CURB-65 criteria consist of age over 65 years, altered mental status, serum blood urea greater than 19.6 mg/dl, respiratory rate more than 30 breaths per minute, and diastolic blood pressure less than 60 mm Hg. A patient who meets two or more of these criteria suggests severe CAP, and admission to the hospital is recommended.

ATS modified criteria are divided into the major criteria of the need for mechanical ventilation or for vacopressors (septic shock) and the minor criteria of respiratory rate greater than 30/min, PaO2/FIO2 ratio less than 250, and bilateral or multilobar infiltrates. At least one major or two minor criteria present on the ATS criteria would define severe pneumonia, which requires ICU admission. However, the use of these scoring systems should not replace physician clinical judgment in deciding about the site of care.

Initial treatment includes assurance of adequate oxygenation, ventilation, and hydration. Antibiotic selection is based on the severity of illness, the likelihood of resistance, and the presence of comorbidities. Outpatient treatment of CAP in an otherwise healthy individual consists of macrolide (azithromycin or clarithromycin) or doxycycline. For patients with comorbidities or antibiotic use in the past three months, use of either a fluoroquinolone (e.g., levofloxacin or moxifloxacin) or a beta-lactam (e.g., amoxicillin +/- clavulanate) plus a macrolide is recommended.

For hospitalized patients, initial antibiotic selection must take into account whether the patient is at risk for pseudomonas infection. Risk factors include a history of broad-spectrum antibiotic therapy for more than 7 days in the past month, bronchiectasis, malnutrition, human immunodeficiency virus infection, chronic immunosuppression with prednisone greater than 10 mg a day, and prior pseudomonas aeruginosa infection.

If there is no risk for pseudomonas infection, first-line therapy consists of a B-lactam (ceftriaxone, 1-2gr intravenous (IV) Q24 hr or cefortaxime, 1-2 gr IV q6-8) plus quinolone IV (levofloxacin, 500-750 mg IV daily; moxifloxacin 400 mg IV daily or gatifloxacin 400 mg daily) or azithromycin (1gr; then, 24 hours later 500 mg IV every 24 hours).

If there is a risk for pseudomonas infection, therapy consists of a carbepenem (imipenem 500 mg IV q6h or meropenem 1gr q8hrs) or anti-pseudomonal cephalosporin (cefepime, 2gr IV q8h or ceftazidime 2gr IV q8hrs) or pipercacillin/tazobactam 4.5gr IV q6hrs plus a quinolone IV (levofloxacin 500-750 mg IV daily; moxifloxacin 400 mg IV daily or gatifloxacin 400 mg daily) or azithromycin (1gr; then, 24 hours later 500 mg IV every 24 hours).

If the patient is severely ill, the clinician should consider adding coverage for methicillin-resistant S.aureus (MRSA) with vancomycin 1gr IV q12hrs until cultures are available.

If the patient has poor dental hygiene, putrid sputum, or a history of alcoholism, the clinician should ensure anaerobic coverage with ceftriazone, cefotaxime (see doses above), clindamycin (450 mg PO q6hrs or 300-900 mg IV q6-12hrs), Metronidazole (500 mg q12hrs PO), piperacillin/tazobactam (4.5 g IV q6hrs), ampicillin/sulbactam (1.5-3 gr IV q6hrs), or Imipenem (500 mg q6hrs).

In cases where a single pathogen is identified, antibiotic therapy can be tailored as follows:

  • Bacteremic Streptococcus pneumoniae:

    • Combination of therapy with beta-lactam plus macrolide or fluoroquinolone

    • Intermediate resistance to penicillin (<2 mg/dl): third-generation cephalosporine or respiratory fluoroquinolone

    • High level of resistance to penicillin (>2 mg/dl): respiratory fluoroquinolone, linezolid, vancomycin

  • Staphylococcus aureus methicillin-susceptible (MSSA)

    • Third-generation cephalosporine, respiratory fluoroquinolone, or clindamycin

  • Staphylococcus aureus methicillin-resistant (MRSA)

    • Vancomycin or linezolid

  • Atypical: Chlamydophila pneumoniae, Mycoplasma pneumoniae and Legionella spp

    • Respiratory fluoroquinolone, macrolide, or doxycycline (not for Legionella spp)

  • Hemophilus influenzae

    • Amoxicillin

    • Beta-lactamase producer: third-generation cephlosporin, beta-lactam/betalactamse inhibitors, or a fluoroquinolone, newer macrolide (clarithromycin or azithromycin) or doxycycline

  • Enterobacteriaceae, including E.Coli, Klebsiella pneumoniae, Klebsiella oxytoca, and Proteus mirabilis

    • Third-generation cephalosporin, beta;actam/beta;actamse inhibitors or a fluoroquinolone.

  • Pseudomonas aeruginosa

    • Intravenous anti-pseudomonal beta-lactam/beta-lactamase inhibitor plus either intravenous aminoglycoside or intravenous ciprofloxacin/levofloxacin, plus intravenous macrolide if aminoglycoside is used, but not with the use of ciprofloxacin/levofloxacin

  • Coxiella burnetti or Chlamydophila psittaci

    • Macrolide or doxycycline

  • Influenza

    • Ostltamivir or zanamivir (covers both influenza A and B)

What is the prognosis for patients managed in the recommended ways?

A decrease in mortality rates has been associated with early and appropriate antibiotic therapy. In-patient mortality is estimated to be around 8 percent, with half of the deaths being due to pneumonia and half to comorbid illness. Respiratory failure, sepsis, and heart disease are the most common immediate causes of death. P. aeroginosa infections are associated with the highest mortality rates--in excess of 50 percent in some series. Dementia, immunosuppression, active cancer, systolic hypotension, male gender, and mutilobar infiltrates are factors other than pneumonia that are independently associated with mortality in CAP.

Approximately 10 to 15 percent of patients will have another episode of pneumonia in the next two years.

What other considerations exist for patients with community-acquired pneumonia?

Patients over age forty and all tobacco smokers should have a follow-up chest x-ray after an episode of CAP to ensure radiographic resolution and exclude the possibility of an underlying malignancy. There is often a delay in radiographic resolution of up to six weeks in otherwise healthy individuals and up to twelve weeks in the elderly and those with underlying COPD.

If there is no clinical improvement in the acute setting or no radiographic improvement on follow-up chest x-ray obtained at the appropriate interval, the clinician should consider:

  • a resistant pathogen, such as methicillin-resistant S. aureus (MRSA)

  • An unusual pathogen, such as MTb, Pneumocystis, or a fungal pathogen

  • a non-infectious mimicker of pneumonia, such as bronchiolitis obliterans organizing pneumonia (BOOP), vasculitis, hypersensitivity pneumonitis, or bronchogenic carcinoma

  • proximal bronchial obstruction

  • the presence of an undrained focus of infection (empyema, lung abscess, brain abscess, endocarditis, splenic abscess, or osteomyelitis)

  • drug-induced fever

What’s the evidence?

Niederman, MS, Mandell, LA, Anzueto, A, Bass, JB, Broughton, WA, Campbell, GD. "Guidelines for the management of adults with community acquired pneumonia. Diagnosis, assessment of severity, antimicrobial therapy and prevention". Am J Respir Crit Care Med. vol. 163. 2001. pp. 1730-1754.

Important guidelines document issued by the American Thoracic Society.

Woodhead, M, Blasi, F, Ewig, S, Garau, J, Huchon, G, Leven, M. "Joint Taskforce of the European Respiratory Society and European Society for Clinical Microbiology and Infectious Diseases. Guidelines for the management of adult lower respiratory tract infections--summary". Clin Microbiol Infect. vol. 6. 2011. pp. 1-24.

A European guidelines document that provides up-to-date, evidence-based recommendations on the management of pneumonia, including CAP.

Tejerina, E, Frutos-Vivar, F, Restrepo, MI, Anzueto, A, Palizas, F, Gonzalez, M. "Prognosis factors and outcome of community-acquired pneumonia needing mechanical ventilation". J Crit Care. vol. 20. 2005. pp. 230-238.

This retrospective study of patients with CAP requiring mechanical ventilation demonstrates that the main determinants of outcome were the initial severity of illness and the development of shock and/or acute renal failure.

Marrie, TJ, Carriere, KC, Jin, Y, Johnson, DH. "Factors associated with death among adults <55 years of age hospitalized for community-acquired pneumonia". Clin Infect Dis. vol. 36. 2003. pp. 413-21.

Documents in-hospital case-fatality rates for the first ten days of hospitalization and overall rates of 2.1 percent and 3.2 percent, respectively, for 11,684 patient hospitalizations.
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