MANAGEMENT OF COMMUNITY-ACQUIRED PNEUMONIA

This article discusses the current management of Community Aquired Pneumonia as based on the Canadian guidelines for the initial management of community-acquired pneumonia: An evidence-based update by the Canadian Infectious Diseases Society and the Canadian Thoracic Society as published in Clin Infect Dis 2000;31:383-421.

Who gets CAP?

Anyone can get pneumonia but incidence rates are highest at the extremes of life. Persons between 4-45 years of age have a 1 in a 1000 chance of getting CAP. Between the age of 46-65 the rate increases to almost 3 per 1000 person and then rises exponentially to as high as 17 per 1000 in those over the age of 65. Dementia, alcoholism, congestive heart failure, chronic obstructive pulmonary disease and overcrowding are some of the factors that increase the risk of developing pneumonia.

Etiology of Pneumonia

There are over 100 microbial causes of CAP. In the majority of cases, there are no specific signs, symptoms, laboratory or roentgenologic features defining a particular etiology. Therefore, an empiric approach to treatment is recommended based on the likelihood of specific pathogens based on severity of disease and certain specific risk factors (discussed below).

How Do I Diagnose CAP?

Patients presenting with fever, new cough productive of purulent sputum and focal abnormalities on examination of the chest should be suspected of having pneumonia. Having said this, the reliability of the history and physical exam alone has not been prospectively tested and remains unknown. No combination of symptoms or signs allows pneumonia to be definitively diagnosed or excluded. If a patient has normal vital signs and a normal physical exam the probability of pneumonia is low and there is no need for further examination1 (Level 3 evidence).

Should I Order Any Tests?

A chest roentgenogram is the standard way of confirming CAP and is recommended for the routine evaluation of patients suspected of having the disease.

Unless the patient looks sick (i.e. heart rate >100/min., respiratory rate >24breaths/min, and oral temperature >38°C) or has comorbid disease or radiographic risk factors for poor outcome (pleural effusion, multilobar, cavitary disease), routine laboratory assessment of ambulatory patients is not recommended. Patients directed to an emergency room should have a complete blood count, electrolyte levels, liver and renal function tests and oxygen saturation measured. This value can be used in the prediction rule developed by Fine et al and has been prospectively validated in determining mortality risk2 (Level 3 evidence).

Should I Send Off A Sputum Sample?

There are a number of difficulties with the use of sputum samples in an outpatient setting. Many patients can not provide a sample. This is especially true in elderly patients. Sputum samples must be promptly transported to a laboratory (within 1-2 hours) which is extremely difficult in an outpatient setting. Finally, identification of an adequate sample containing <25 squamous epithelial cells per low-power field requires specialty trained staff whom are normally not available in community laboratories. In routine clinical practice causative pathogens are found in <25% of CAP cases and lead to a change in therapy in <10% of cases3 (Level 3 Evidence).

For the majority of patients treated on an outpatient basis, no specific microbiological investigations are recommended. Exceptions include clinical circumstances where infections with Mycobacterium tuberculosis, Pneumocystis carinii or endemic fungi are suspected and direct staining of sputum would be diagnostic.

Treatment of CAP

What Has Changed Between The 1993 To 2000 Guidelines?4 (Level 4 Evidence)

  1. Simplification of modifying factors. Many of the comorbid conditions considered in the 1993 guidelines (e.g. congestive heart failure, renal failure, diabetes, etc.) are no longer significant in choosing specific therapy. Their importance now lies in their contribution to the pneumonia score that helps determine site of care (see below). The major modifying factors that must be considered include presence of COPD, recent use of antibiotics and risk of aspiration.
     
  2. Site of care. Prediction rules have been developed and validated that are useful for predicting mortality in CAP patients2 (Level 3 evidence). Although not necessarily tested as a vehicle for determining which patient can be safely treated as an outpatient, they do help guide decisions as patients with low risks of mortality can usually be treated as outpatients. The overall pneumonia-specific severity of illness score is cumbersome to calculate and probably not practical in an outpatient setting. However, low risk patients can be quickly identified in the office and they can comfortably be treated as outpatients assuming that the social situation makes this feasible.

    Low risk patients are:

    1. less than 50 years of age
    2. absence of neoplastic, cerebrovascular, renal or liver disease. No congestive heart failure.
    3. normal mental status, pulse <125 bpm, respiratory rate <30/minute, systolic blood pressure >90 mmHg, temperature >35° C and <°40 C.

     
  3. Importance of macrolides or fluoroquinolones as part of initial antimicrobial therapy. The bacterial organisms responsible for the majority of CAP cases (Streptococcus pneumoniae, Mycoplasma pneumonia, Chlamydia pneumoniae, Legionella species and Haemophilus influenzae) are usually susceptible to these two classes of medication. Inclusion of a macrolide or fluoroquinolone in initial empiric CAP treatment is associated with improved survival5 (Level 3 Evidence).

How Do I Treat?4 (Level 4 Evidence)

  1. Outpatient without modifying factors - treatment of choice is a macrolide (erythromycin, azithromycin or clarithromycin). For macrolide intolerant or allergic patients doxycycline is a second choice.
     
  2. Outpatient with modifying factors
     
    1. COPD (no antibiotics or oral steroids within past 3 months). Because of the increased risk of Haemophilus influenzae (not sensitive to erythromycin) extended spectrum macrolides (azithromycin or clarithromycin) are recommended. Doxycline is again a second choice for macrolide allergic or intolerant patients
       
    2. COPD (antibiotics or oral steroids within past 3 months). Aside from more common CAP pathogens, this group of patients is at an increased risk of infection with gram negative rods. Therefore, a respiratory fluoroquinolone (levofloxacin, moxifloxacin or gatifloxacin) is recommended. An alternative regimen combines a macrolide with either amoxicillin/clavulanate or a second generation cephalosporin (e.g. cefuroxime, cefprozil, etc.)
       
    3. Suspected macroaspiration - Patients with periods of decreased consciousness (seizures, drug overdoses, alcohol or neurologic diseases affecting the swallowing mechanism). Antibiotics with enhanced activity against anaerobes should be considered. Amoxicillin/clavulanate with or without a macrolide is the first choice. An appropriate alternative would be a third generation fluoroquinolone plus either metronidazole or clindamycin
       
  3. Nursing Home Resident - at risk for enteric gram-negative rods in addition to more common pathogens. First choice is a respiratory fluoroquinolone alone or amoxicillin/clavulanate combined with a macrolide. A second generation cephalosporin with a macrolide is an alternative.
     
  4. CAP patients hospitalized on medical ward - treatment is directed at bacteremic pneumococcal pneumonia as well as infection with H. influenzae, enteric gram-negative bacilli or severe atypical (legionella, chlamydia) infection. Monotherapy with a respiratory fluoroquinolone is the first choice. An alternative regimen combines a macrolide with a second, third or fourth generation cephalosporin.

Summary

An empiric approach to CAP therapy is recommended. The following should be considered:
  • confirm diagnosis with chest roentgenogram
     
  • S. pneumoniae and atypicals (legionella, mycoplasma, chlamydia) must be covered in all patients
     
  • consider specific comorbid illness, i) COPD and ii) predisposition to aspiration
     
  • determine site of care: outpatient versus inpatient versus nursing home
     
  • consider site of acquisition of pneumonia, i) community at large, ii) nursing home

- Meyer Balter

Thanks to Dr. Dennis Bowie, Consultant Respirologist at the Queen Elizabeth II Health Sciences Center in Halifax, Nova Scotia, for reviewing the draft copy of this article.

References:

  1. Metlay JP, Kapoor WN, Fine MJ. Does this patient have community-acquired pneumonia? Diagnosing pneumonia by history and physical examination. JAMA 1997;278:1440-5.
     
  2. Fine MJ, Auble TE, Yealy DM, et al. A prediction rule to identify low-risk patients with community-acquired pneumonia. JAMA 1997;336:243-50.
     
  3. Woodhead MA, Arrowsmith J, Chamberlain-Webber R, et al. The value of routine microbiological investigations in community-acquired pneumonia. Respir Med 1991;85:313-7.
     
  4. Mandell LA, Marrie TJ, Grossman RF, et al. Canadian guidelines for the initial management of community-acquired pneumonia: An evidence-based update by the Canadian Infectious Diseases Society and the Canadian Thoracic Society. Clin Infect Dis 2000;31:383-421.
     
  5. Houck PM, MacLehose RF, Niederman MS, Lowery JK. Empiric antibiotic therapy and mortality among medicare pneumonia inpatients in 10 western states: 1993, 1995 and 1997. CHEST 2001;119:1420-6.

You can search for abstracts of the above references by following this link: PubMed

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