What
are the most common causes of CAP? Although pneumococcus remains the most commonly identified
cause of CAP, the frequency with which it is implicated has declined, and it
is now detected in only about 10 to 15% of inpatient cases in the United
States. Other bacteria that cause CAP include Haemophilus influenzae,
Staphylococcus aureus, Moraxella catarrhalis, Pseudomonas aeruginosa, and
other gram-negative bacilli. Patients with chronic obstructive pulmonary
disease (COPD) are at increased risk for CAP caused by H. influenzae
and Mor. catarrhalis. P. aeruginosa and other gram-negative
bacilli also cause CAP in persons who have COPD or bronchiectasis, especially
in those taking glucocorticoids. There is a wide variation in the reported
incidence of CAP caused by Mycoplasma pneumoniae and Chlamydophila
pneumoniae (so-called atypical bacterial causes of CAP), depending in
part on the diagnostic techniques that are used. During influenza outbreaks,
the circulating influenza virus becomes the principal cause of CAP that is
serious enough to require hospitalization, with secondary bacterial infection
as a major contributor.
What
evaluation do the authors recommend to determine the cause of
community-acquired pneumonia in a hospitalized patient? In hospitalized patients with CAP,
the authors favor obtaining Gram’s staining and culture of sputum, blood
cultures, testing for legionella and pneumococcal urinary antigens, and
multiplex PCR assays for Myc. pneumoniae, Chl. pneumoniae, and
respiratory viruses, as well as other testing as indicated in patients with
specific risk factors or exposures. A low serum procalcitonin concentration
(<0.1 µg per liter) can help to support a decision to withhold or
discontinue antibiotics. Results on Gram’s staining and culture of sputum are
positive in more than 80% of cases of pneumococcal pneumonia when a
good-quality specimen (>10 inflammatory cells per epithelial cell) can be
obtained before, or within 6 to 12 hours after, the initiation of
antibiotics. Blood cultures are positive in about 20 to 25% of inpatients
with pneumococcal pneumonia but in fewer cases of pneumonia caused by H.
influenzae or P. aeruginosa and only rarely in cases caused by Mor.
catarrhalis.
What
are the guidelines for treating community-acquired pneumonia in outpatients
and inpatients? For
outpatients without coexisting illnesses or recent use of antimicrobial
agents, IDSA/ATS [Infectious Diseases Society of America and the American
Thoracic Society] guidelines recommend the administration of a macrolide
(provided that <25% of pneumococci in the community have high-level
macrolide resistance) or doxycycline. For outpatients with coexisting
illnesses or recent use of antimicrobial agents, the guidelines recommend the
use of levofloxacin or moxifloxacin alone or a beta-lactam (e.g., amoxicillin–clavulanate)
plus a macrolide. The authors argue, however, that a beta-lactam may be
favored as empirical therapy for CAP in outpatients, since most clinicians do
not know the level of pneumococcal resistance in their communities, and Str.
pneumoniae is more susceptible to penicillins than to macrolides or
doxycycline. Even though the prevalence of Str. pneumoniae as a cause
of CAP has decreased, they raise concern about treating a patient with a
macrolide or doxycycline to which 15 to 30% of strains of Str. pneumoniae
are resistant. For patients with CAP who require hospitalization and in whom
no cause of infection is immediately apparent, IDSA/ATS guidelines recommend
empirical therapy with either a beta-lactam plus a macrolide or a quinolone
alone.
What
is the appropriate duration of antibiotic therapy for community-acquired
pneumonia?
Early in the
antibiotic era, pneumonia was treated for about 5 days; the standard duration
of treatment later evolved to 5 to 7 days. A meta-analysis of studies
comparing treatment durations of 7 days or less with durations of 8 days or
more showed no differences in outcomes, and prospective studies have shown
that 5 days of therapy are as effective as 10 days and 3 days are as
effective as 8. Nevertheless, practitioners have gradually increased the
duration of treatment for CAP to 10 to 14 days. The authors argue that a
responsible approach to balancing antibiotic stewardship with concern about
insufficient antibiotic therapy would be to limit treatment to 5 to 7 days,
especially in outpatients or in inpatients who have a prompt response to
therapy. Pneumonia that is caused by Staph. aureus or gram-negative
bacilli tends to be destructive, and concern that small abscesses may be
present has led clinicians to use more prolonged therapy, depending on the
presence or absence of coexisting illnesses and the response to therapy.
Summary
- Strep pneumo still is the most common bug, and is more sensitive to penicillins than macrolides or doxy.
- Uncomplicated, outpatient treatment: Macrolide or Doxy, consider adding a beta-lactam if high risk; alternatively, respiratory quinolone by it self.
- Sputum gram stain and cultures.. maybe, don't expect to get too much from them.
- 5 days of treatment is as good as 10.
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Thursday, October 23, 2014
Community Acquired Pneumonia - Keep it simple, but not too simple.
One of the oldest (and deadliest) diseases in history, pneumonia continues being a threat. Recognizing and treating properly are the best way to minimize complications. Another good review from this week's NEJM.
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