Community Acquired Pneumonia
Match the Treatment to the Patient

Pneumonia remains a common infection that affects both ambulatory and inpatient populations. The overall attack rate for community acquired pneumonia (CAP) is 12 per 1,0000 population per year and up to 20-50% of all patients with pneumonia will require hospitalization. It is observed that the incidence of pneumonia is increasing due to the aging of the population and the greater proportion of the population surviving with chronic medical illnesses (cancer, alcoholism, COPD, diabetes, renal failure, etc). The decision to hospitalize a patient carries with it important economic and prognostic implications. Data are available from the US where the cost of hospitalization for CAP is US$ 4 billion per year in that country alone.

Diagnosis

Pneumonia is defined as an acute infection of the pulmonary parenchyma that is associated with symptoms of infection (fever, cough, purulent sputum) along with an infiltrate on chest x-ray and/or auscultatory findings consistent with pneumonia (altered breath sounds or localized rales). To have CAP the patient cannot have been hospitalized or residing in a long-term care facility 14 days prior to onset of symptoms of pneumonia. A two-view chest x-ray is advised in all patients likely to have pneumonia. The clinical diagnosis of pneumonia has been estimated to be correct in 3 % of patients in the general population and in about 28% of ED patients; thus reliance on historical, physical findings and clinical judgement to make the diagnosis will generally be incorrect and result in substantial overuse of antibiotics. False negative chest x-ray results (rare) can be attributed to dehydration, evaluation during first 24 hours, pneumonia due to Pneumocystis Carnii(PCP) (common) or pneumonia due to profound neutropenia.

Risk Factor Stratification

A great deal of work has focused on the identification of factors that predispose to death or severe illness from pneumonia. This has allowed the development of clear criteria to aid in the decision of who to admit and who to follow as outpatients. Patients at risk from this disease include the elderly, those with severe co-morbid illnesses and those who are immunocompromised. Patients who are otherwise healthy are at increased risk if they have organ dysfunction due to septic shock or hypoxia of if there is an inability to provide adequate follow-up care. The CAP Pneumonia Severity Index (PSI) was based on studies looking at mortality risk factors in patients with this disease. From these studies a comprehensive scoring system (PSI) has been devised to determine which patients require hospital admission.

Points are assigned based on risk factors identified on history, physical exam and basic laboratory investigations (Table 1). The final cumulative score then correlates with the severity of the illness and gives an objective assessment of the patient's mortality of the illness.

Patients in risk class I and II have very low adverse outcomes and thus can be managed safely in an outpatient setting if they do not require supplemental oxygen and are able to receive their antibiotics at home. Patients in risk class III have an intermediate risk and may require brief hospital admission. Patients belonging to risk classes IV and V have an unacceptably poor outcome and thus require traditional inpatient management.

I have been using risk scoring along with my colleagues for the past three years. It takes all of two minutes to do. I find it very useful in deciding if my patients older than 50 can safely go home. I always put my PSI on the chart and document my reasoning if I'm going to discharge home a patient with a PSI of 111 or greater. The other caveat to using the PSI is hypoxemia alone may be the only indication for admission. As well, certain psychosocial issues may necessitate inpatient treatment, despite a low PSI score. PSI should be used as a tool, understanding that clinical judgement always rules the day.

Diagnostic Testing

A two-view chest x-ray is advised in all patients with pneumonia. Radiographic changes usually cannot be used to distinguish between types of bacterial and non-bacterial pneumonia. They are often important in evaluating severity of illness (pleural effusion, multilobar) and the need for diagnostic studies. Computed tomography is considered more sensitive then radiography for detecting infiltrates and may be especially useful in detecting interstitial disease, empyema, cavitation, multifocal disease, and adenopathy.

A chest x-ray alone is all that is required in young healthy patients with no co-morbid disease and stable vital signs. Baseline blood work (CBC, electrolytes, renal function, glucose, and venous gas) is required for patients assigned to class II-V based on the first step of the PSI algorithm in order to further assign risk.

The microbiological work-up of the pneumonia patient remains controversial. In contrast to the complete microbiological work-up recommended by the Infectious Disease Society of Canada (and ISDA), the American Thoracic Society gives this much less emphasis. The problems with sputum Gram stain and culture are many:

1. Many patients don't produce sputum
2. Collecting specimen may delay administration of antibiotic
3. Poor collective methods, yielding inadequate samples
4. Lack of sensitivity
5. Results rarely change management

The same can be said regarding blood cultures:

1. Only 10% will be positive
2. Of these 60% will be Steptococcus. Pneumonia
3. Results rarely change management (2% of cases)

Perhaps a more practical use of microbiological testing would be:

1. Test only the most severely ill patients (class V and ICU)
2. Test patients whom you suspect may have an unusual pathogen (TB, resistant Step. Pneumonia, PCP.
3. Test as part of a surveillance program to monitor pathogen and resistance patterns in your community

Serologic testing of atypical bacteria should be reserved for epidemiological purposes only. Legionella urinary antigen test should be part of the routine management of severe CAP, especially if patients are admitted to the ICU. DNA probes and amplification are being developed to assist clinicians with the rapid and accurate diagnosis of problem pathogens such as Chlamydia pneumonia and Mycoplasma pneumonia.

Etiology of Community Acquired Pneumonia

The most common pathogens causing pneumonia in order of frequency are Streptococcus Pneumonia, Mycoplasma Pneumonia, Hemophilus Influenzae, Legionella, Chlamydia, and Moraxella Catarrhalis. Less common (<2%) include Staphylococcus Aureus, Gram Negative Bacilli, Anaerobes and Pseudomonas. Certain host modifying factors may predispose patients to less common pathogens.

Empirical Antimicrobial Selection for CAP

Outpatient Treatment

1. Most young, healthy patients with no co-morbid disease can be treated with a macrolide or doxycycline. The same is true for the patient with chronic obstructive lung disease (COLD) who has had no antibiotics or steroids in the past 3 months. The only caveat is that erythromycin is not a good choice for COLD patients given its limited H. Influenza coverage. Sulfamethoxazole/trimethoprim (Septra, Bactrim) is no longer an acceptable antibiotic for CAP because of Streptococcus Pneumonia resistance.
2. COLD patients with recent antibiotic or steroid use and patients residing in long term facilities are slightly more at risk for enteric gram negative bacteria and penicillin resistant Streptococcus Pneumonia (PRSP) and should be covered with either:
1. A Respiratory Fluoroquinolone alone or
2. Combination Betalactam/Betalactam Inhibitor + a Macrolide or
3. Combination second generation cephalosporin + a macrolide.
3. Patients suspected of having a macroaspiration implicating oral anaerobes with be treated with:
1. Betalacatam/Betalactam Inhibitor +/- a Macrolide
2. Respiratory Fluoroquinolone and Clindamycin or Metronidazole

In my practice I really try to keep my antibiotic choices simple. In young healthy patients I cycle between Doxycycline and a Macrolide. I also cycle between my classes of Macrolides. I don't see any role for respiratory Fluroquinolones in this group unless there is an allergy to the two above or treatment failure (rare). In older patients with co-morbid disease I usually try to keep my choice to a monotherapy, using either a new generation Macrolide or a respiratory Fluroquinolone. (dependant on risk of gram negatives or S. Pneumonia resistance). The main advantage of the respiratory Fluroquinolones is their excellent oral bioavailability. (equivalent to 90% of the IV bioavailability).

Inpatient Treatment

1. Most patients cared for on the ward can be treated with any of the following:
1. Second or third cephalosporin + a macrolide
2. Betalactam/Betalactam inhibitor + a macrolide
3. Respiratory Fluoroquinolone alone. (iv or po dependant on GI function )

It is important to note that all three of these regimes have equal clinical efficacy. In general, you can ignore what the pharmaceutical representatives tell you about microbiological efficacy, as it means nothing in pneumonia. Treatment failures in the above group are mostly related to host factors, rather than inappropriate antibiotic selection. The only exception would be failing to consider Aspiration, Pseudomonas or highly resistant PRSP (which a 3G cephalosporin would usually take care of) in "at risk" patients.

2. Patients admitted to the ICU not suspected to have Pseudomonas should always be treated with combination treatment of either:
1. 3G Cephalosporin + a Macrolide or a Respiratory Fluoroquinolone
2. Betalactam/Betaalctam Inhibitor + a Macrolide or a Respiratory Fluoroquinolone.
 

3. Patient suspected of having Pseudomonas should be treated with either of the following combinations:
1. Antipseudomonas Fluoroquinolone (e.g. Ciprofloxaxin) + a Antipseudomonas Betalactam or Aminoglycoside
   NOTE: Respiratory Fluoroquinolones don't cover Pseudomonas very well
2. Antipseudomonas Betalactam (e.g. Ceftazidime) + aminoglycoside + macrolide

Antimicrobial Resistance

There has been much hype in the media and the literature regarding antimicrobial resistance, mostly concerning Streptococcus Pneumonia. Clearly Penicillin Resistance Streptococcus Pneumonia (PRPS) has important clinical implications in the treatment of meningitis and otitis media. However the clinical implications of PRPS in the treatment of pneumonia are less clear. Mean Inhibitory Concentration (MIC) is based on drug concentration in serum not in lung parenchyma. We know that most of the commonly used antibiotics for treatment of pneumonia are highly concentrated in the lung parenchyma, and most can overcome intermediate and in some instances highly resistant PRPS, just by increasing the dose. Most intermediate to high resistant PRPS are still sensitive to third generation cephalosporin (Ceftriaxone and Cefotaxime).

Clearly we as clinicians have to take some responsibility in controlling antimicrobial resistance. First and foremost we must be diligent in not treating clearly viral illnesses. We must also cycle our antibiotic prescribing so that we're not always using the same antibiotic.

- Dr. Chris Vaillancourt

Thanks to Dr. Scott Rappard, Respirologist at St. Martha's Regional Hospital in Antigonish, Nova Scotia, Canada for reviewing the draft copy of this article.

References:

1. American Thoracic Society, Guidelines for the Initial Management of Adults with Community-acquired Pneumonia: Diagnosis, Assessment of Severity, and Initial Antimicrobial Therapy. Am J Respir Crit Care Med Vol 163. Pp 1730-1754 2001

 
2. Guidelines from the Infectious Diseases Society of America, Practice Guidelines for the Management of Community Acquired Pneumonia in Adults. Clinical Infectious Diseases 2000; 31:347-82

 
3. Management of Community Acquired Pneumonia in the Era of Pneumococcal Resistance: A Report from the Drug-Resistant Streptococcus Pneumonia Therapeutic Working Group. Arch Intern Med/Vol 160, May 22 2000

 
4. Canadian Guidelines for the Initial Management of Community-Acquired Pneumonia: An Evidence-Based Update by the Canadian Infectious Disease Society and the Canadian Thoracic Society. Clinical Infectious Disease 2000 31: 383-421

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