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Community-Acquired Pneumonia

With community-acquired pneumonia, there has been an increasing incidence of resistant respiratory pathogens; there are about 4 million pneumonias annually and in terms of some of the other infections, like acute otitis media, there are upwards of 20 million visits annually to physician offices in the U.S. Of the pneumonias, about 3 million are managed in the outpatient setting and another million, or about one-fourth of all the cases, are managed in the inpatient setting.

We will talk about the community-acquired pneumonias first. This is a major cause of death worldwide. Community-acquired pneumonia is the sixth leading cause of death in the United States. The management of this disease has been controversial and confusing. In the 1990's, several different professional organizations in the United States and abroad developed and published guidelines on the management of community-acquired pneumonias and other respiratory infections.

The pathogens associated with community-acquired pneumonia are the following: Strep. pneumoniae is the most common pathogen in virtually all series of community-acquired pneumonias. I am aware of one series in which legionella actually turned to be the most common pathogen in a series from the University of Pittsburgh, but Strep. pneumoniae is the most common pathogen identified. Haemophilus influenzae generally is second, Mycoplasma pneumoniae varies with the demographics of the population. Generally, Mycoplasma pneumoniae is not a significant problem by the end of the third decade, so when you are starting to see adults getting towards middle age, Mycoplasma pneumoniae becomes less common.

Gram-negative bacilli become more common as people age and are more common in the nursing home population. Respiratory viruses are also an important cause of community-acquired pneumonia. The significant agents there are adenovirus, influenza pneumonia and parainfluenza. Respiratory syncytial virus is typically a disease of the very young but can occur in adults as well and can be very virulent in patients.

Individuals who are older than 50, let's say 55, and are tachycardic at 125, that would take them up to around 75 points, which would take them into category III. Pick one of the 10-point laboratory values and that puts you into category II for a predicted mortality of 0.6%, so you are well under 1% here and the recommended site of care is the out-patient setting.

As you start to add on other predictors of mortality, underlying disease, laboratory abnormalities, significant physical findings, this number is 2.8%, but it represents a nearly five-fold increase in predicted mortality over category II, so this is a group that you might want to pay a little closer attention to. You might want to have them in the hospital overnight to see if they respond to their first couple doses of antibiotics before sending them home. So category III is on the fence - either its an out-patient management situation or a brief in-patient setting to ensure improvement.

The Infectious Diseases Society of America, as I mentioned, was one of the groups that published guidelines. Its guidelines were published in April 2006 in the Journal of Clinical Infectious Diseases. It is a very lengthy document. It was really published in retaliation to the American Thoracic Society guidelines, which had been published a few years before. The American Thoracic Society (ATS) guidelines really advocated the use of empiric therapy for the treatment of community-acquired pneumonia. Their rationale was that the diagnostic tools available to us were not very good at that point in time in the mid 1990's, and they're still not great. They are limited by the ability of the patient to produce sputum; they are limited by the availability of rapid diagnostic tests; and based on a very reasoned review.

The guidelines in the out-patient setting is a very clear recognition that we are operating with one hand tied behind our backs; we have our clinical judgment to guide us, but as I've said, the clinical findings do not distinguish between the various community-acquired pneumonias very well. Our hands are tied behind our back because of the inability to have office laboratories unless you want to go through the CLIA certification process, so many of us are in the position of ordering labs, having them picked up by a commercial laboratory at the end of the day or at several points during the course of the day, and then getting a report back the next day or the following day, whereas in an office setting, if you had the time, a gram stain could be done and you would have a good sense, based on the appearance of the gram stain, whether you are dealing the community-acquired pneumonia from Strep. pneumoniae or Haemophilus influenza or perhaps another pathogen. It is useful when you don't see anything under the microscope. If you see polymorphs and no bacteria, that should have you thinking about atypical pathogens and tuberculosis and some of the atypicals. So blood cultures should be done for all in-patients. They are not positive very often; they are only positive about ten percent of the time, but they are positive about a third of the time in patients with pneumococcal pneumonia. So a blood culture is useful in diagnosing pneumococcal pneumonia and with the rising incidence that we have discussed of penicillin-resistant Strep. pneumoniae, it is useful to have that isolate and to be able to test it and make appropriate modifications in therapy.

Regarding gram stain and culture of sputum, the literature would suggest that it has poor predictive value, because it is often contaminated with respiratory flora. In the hands of a good clinical microbiologist or someone who is accustomed to looking at gram stains, I believe that they are very useful in guiding initial therapy. I have treated injection drug users who had pneumonias and I looked under the microscope and when I saw pneumococcus, I felt very comfortable that I was dealing with pneumococcus. I think in the hands of someone who looks at it a lot, it is a useful test. Tests for specific pathogens should be based on risk factors. If your patient is a heating, ventilation and air conditioning cleaner and he comes in with a week-long cough and a patchy infiltrate on his x-ray, you ought to be thinking about Legionella. If he has not responded to therapy, you ought to be thinking about Legionella. If he is in a risk group for tuberculosis, you ought to be isolating him and ordering the appropriate tests. If there is a significant pleural effusion, thoracentesis ought to be done, as diagnosis is often obtained out of the pleural fluid. More invasive procedures, such bronchoscopy, ought to be relegated to patients who are more severely ill, where there is no diagnosis, or immunocompromised patients. In immunocompromised patients, you have to get tissue. The differential is so broad and the treatments are so varied that when you have a transplant recipient come in, you really have to get a piece of that lung and find out what they have. If they have an HIV infection and the clinical course is characteristic and the radiograph is characteristic, treating initially for Pneumocystis carinii pneumonia with trimethoprim sulfa or pentamidine is appropriate initially, but if they don't respond within the first few days, you really have to be more aggressive and go to bronchoscopy.

Gram stain has limitations as a diagnostic tool but this is the tool that is most readily available to us; it's the one that we are able to do with our own hands and interpret quickly. Many patients cannot produce a good sputum specimen. Antibiotics can quickly sterilize the sputum, although the patient may not have recovered from the pneumonia because of the ongoing inflammatory response in the lung. The appearance on gram stain can be altered quickly so it is best to have a fresh sputum specimen. Many specimens show inconclusive results because of the contamination with oral flora, but it can provide a useful guide to diagnosis when there is a predominance of a particular organism seen in the specimen.

In terms of treatment, the IDSA guidelines recommend two categories of treatment. One, when a pathogen is identified and pathogen-directed therapy is appropriate based on in vitro susceptibility tests, so you have to have a clinical specimen to test and get the susceptibility back and the modify the empiric treatment. Category II is the recommendation for patients with no etiologic diagnosis, even after good microbiology has been done, or those who require decisions for empiric antibiotic therapy; that involves most of our patients. Most of our patients will start out in category II and then some will move to category I. Treatment of community-acquired pneumonia.