Community-Acquired Pneumonia

 

I. Introduction:

A. 6th most common cause of death in the U.S.
B. Mortality increasing due to:
1. increasing population over 65
2. increasing prevalence of chronic disease
C. Best clinical guidelines supplied by:
1. American Thoracic Society: "Guidelines for the Initial Management of Adults with Community-acquired Pneumonia Diagnosis, Assessment of Severity and Initial Antimicrobial Therapy" (November, 1993): http://www.thoracic.org
2. Infectious Diseases Society of America: "Community-Acquired Pneumonia in Adults: Guidelines for Management" (1998): http://www.idsociety.org/practice/index.html

II. Etiology

A. identification of the cause of pneumonia is difficult
1. diagnosis undefined in about 50% of cases
2. many pneumonias are polymicrobial; even if an organism is cultured from a normally sterile site (pleural fluid or blood), you do not know if there are additional organisms contributing to the infection
B. outpatient pneumonia in healthy patients age < 60: mortality about 1-5%
1. S. pneumoniae
2. M. pneumoniae
3. respiratory viruses
4. C. pneumoniae
5. H. influenzae
6. Legionella sp.
C. outpatient pneumonia in patients with comorbid diseases or age > 60: mortality about 5% but about 20% ultimately require hospitalization
1. S. pneumoniae
2. respiratory viruses
3. H. influenzae
4. aerobic gram-negative rods
5. S. aureus
6. M. catarrhalis
7. Legionella sp.
D. hospitalized patients with community-acquired pneumonia: mortality about 5-25%
1. S. pneumoniae
2. H. influenzae
3. polymicrobial
4. aerobic gram-negative rods
5. Legionella sp.
6. S. aureus
7. C. pneumoniae
8. M. pneumoniae
9. respiratory viruses
E. hospitalized patients with severe community-acquired pneumonia (ie, those requiring ICU care): mortality about 50%
1. S. pneumoniae
2. Legionella sp.
3. aerobic gram-negative rods
4. M. pneumoniae
5. respiratory viruses
6. H. influenzae
F. Note: For hospitalized patients with community-acquired pneumonia, the incidence of legionella = 3%, mycoplasma = 15%, and chlamydia = 5%

III. Diagnosis

A. clinical presentation
1. there are no characteristic clinical distinguishers
a) clinical features of Legionella are not specific
b) clinical features of Mycoplasma are not specific
2. distinction between "typical" and "atypical" pneumonias are not reliable
3. most valuable features for guiding therapy are age and presence of co-morbid diseases
B. chest x-ray
C. sputum Gram's stain
1. extremely limited utility
2. accuracy surprisingly not well studied
3. if used, should have > 25 WBCs and < 10 squamous cells per low powered field
4. use discouraged by the 1995 American Thoracic Society guidelines for community acquired pneumonia but encouraged (with the disclaimer that use is limited and that sputum culture is even less useful) by the 1998 Infectious Diseases Society of America
D. sputum culture
1. sensitivity & specificity are poor
2. viral cultures not useful as a routine test
3. most helpful when an organism never normally found in the sputum is identified (Legionella, Mycobacteria, fungi, Influenza)
4. some studies indicate that sputum gram stains and cultures do not affect outcome in patients treated according to ATS guidelines (Am J Respir Crit Care Med 1999; 160:346-8)
E. blood cultures
1. routine in patients requiring admission to the hospital
F. invasive diagnostic tests
1. bronchoscopy with protected brush catheter or BAL
a) use in severely ill patients
2. transtracheal aspirate
a) not recommended - bronchoscopy better & safer
3. transcutaneous needle aspirate
a) not recommended - bronchoscopy better & safer
G. thoracentesis
1. perform in patients with > 1 cm of fluid on the lateral decubitus chest x-ray
2. routine pleural fluid studies:
a) cell count & differential
b) protein
c) glucose
d) LDH
e) pH
f) Gram's stain
g) aerobic culture
h) anaerobic culture
3. special pleural fluid studies:
a) mycobacterial culture
b) fungal culture
H. serology
1. not helpful
2. acute & convalescent titers predominately used for epidemiology
a) C. pneumoniae IgM takes about 3 weeks to appear and IgG takes about 8 weeks to appear

IV. Treatment

A. who should be hospitalized?
1. perform risk factor assessment in deciding who should or should not be admitted
2. risks:
a) age > 65
b) co-morbid diseases:
(1) COPD
(2) diabetes
(3) chronic renal failure
(4) congestive heart failure
(5) chronic liver disease
(6) hospitalization within previous 1 year
(7) suspicion of aspiration
(8) altered mental status
(9) s/p splenectomy
(10) malnutrition
(11) chronic alcohol use
c) physical findings:
(1) respiratory rate > 30
(2) diastolic blood pressure < 60
(3) systolic blood pressure < 90
(4) temperature < 35 C or > 40 C
(5) extrapulmonary site of infection
(6) decreased level of consciousness
(7) heart rate > 125/min
d) laboratory findings:
(1) WBC < 4,000 or > 30,000
(2) PaO2 < 60 or PaCO2 > 50
(3) creatinine > 1.2
(4) certain radiographic signs:
(a) more than 1 lobe involvement
(b) cavity
(c) pleural effusion
(5) hemoglobin < 9
(6) metabolic acidosis
(7) DIC
(8) sodium < 130
(9) glucose > 140
e) social support system at home
B. who should be admitted to the ICU?
1. respiratory rate > 30 on admission
2. PaO2/FiO2 < 250
3. mechanical ventilation
4. chest x-ray showing bilateral, multilobar pneumonia with increase in the size of the opacity > 50% in the 48 hours prior to admission
5. systolic blood pressure < 90 or diastolic blood pressure < 60
6. need for vasopressors
7. urine output < 20 ml/hour or acute renal failure
C. what constitutes "severe" community-acquired pneumonia?
1. increased mortality best predicted by:
a) BUN > 21
b) diastolic blood pressure < 60
c) respiratory rate > 30
D. antibiotics - American Thoracic Society Guidelines:
1. outpatient pneumonia in healthy patients age < 60
a) macrolide
(1) erythromycin
(2) azithromycin or clarithromycin
(a) use in patients intolerant to erythromycin
(b) use in smokers because of higher incidence of H. influenzae
b) tetracycline/doxycycline
(1) many strains of S. pneumoniae are resistant to tetracyclines
(2) reserve for patients who cannot take macrolides
2. outpatient pneumonia in patients with comorbid diseases or age > 60
a) second generation cephalosporin or
b) TMP/SMX
c) beta-lactam/beta-lactamase inhibitor
d) erythromycin (or other macrolide)
3. hospitalized patients with community-acquired pneumonia
a) second or third generation cephalosporin ± macrolide
b) beta-lactam/beta-lactamase inhibitor ± macrolide
4. hospitalized patients with severe community-acquired pneumonia (ie, those requiring ICU care)
a) macrolide + third generation cephalosporin (or beta-lactam/beta-lactamase inhibitor) with anti-Pseudomonas activity
(1) add an aminoglycoside until Pseudomonas is excluded
b) macrolide + imipenem/cilastatin
(1) add an aminoglycoside until Pseudomonas is excluded
c) macrolide + ciprofloxacin
(1) add an aminoglycoside until Pseudomonas is excluded
E. Antibiotics - Infectious Diseases Society of America Guidelines:
1. outpatients:
a) preferred drugs:
(1) macrolide
(a) erythromycin
(b) azithromycin or clarithromycin if H. influenza suspected
(2) fluoroquinolone
(a) trovafloxacin
(b) levofloxacin
(c) grepafloxacin
(d) sparfloxacin
(3) doxycycline
b) alternatives:
(1) amoxicillin/clavulanate
(2) some second generation cephalosporins (cefuroxime, cefpodoxime, cefprozil)
2. inpatients not requiring ICU:
a) preferred drugs:
1) beta lactam (cefotaxime or ceftriaxone) with/without macrolide
2) quinolone (alone)
b) alternative drugs:
1) cefuroxime +/- macrolide
2) azithromycin alone
3. inpatients requiring ICU:
a) preferred:
1) erythromycin, azithromycin, or fluoroquinolone
2) PLUS cefataxime, ceftriaxone, or beta lactam/beta lactamase inhibitor
4. bronchiectasis:
a) anti-pseudomonal penicillin, carbapenem, or cefepime
b) PLUS macrolide or fluoroquinolone
c) PLUS aminoglycoside
5. penicillin allergy:
a) fluoroquinolone +/- clindamycin
6. suspected aspiration:
a) fluoroquinoline PLUS clindamycin
b) beta lactam/beta lactamase inhibitor
F. how long do you treat?
1. switch to oral antibiotics when fever has subsided and clinical condition has improved
2. usual bacterial infections: 7-10 days
3. Mycoplasma and Chlamydia: 10-14 days
4. Legionella: 14 days
5. immunocompromised patients: 14-21 days
G. what do you do when the patient does not respond to initial antibiotics?
1. when should the patient improve?
a) clinical improvement may take up to 72 hours
b) fever can last 2-4 days
c) leukocytosis usually resolves by day 4
d) abnormal physical findings may persist > 7 days
e) radiographs may worsen even though clinical picture is improving
f) chest x-ray usually returns to normal within 6 weeks in patients < 60 years of age
2. causes of failure to improve:
a) inadequate antibiotic selection
(1) virus
(2) S. aureus
(3) S. pneumoniae
(a) penicillin-resistant strains account for 15% of isolates in the United States at present; high-grade resistance is considerably less likely. The highest incidence is in children under age 4 yrs and in HIV-infected adults
i) 1994 Franklin County penicillin resistance = 14%
ii) 1994 Franklin County ceftazidime resistance = 24%
iii) 1994 Franklin County trimethoprim-sulfamethoxazole resistance = 24%
(b) erythromycin resistance is increasingly common also
(c) 15 - 20% of pneumococcus is resistant to trimethaprim-sulfamethoxazole
(d) C. pneumonia can exist as a co-pathogen with pneumococcu and contribute to failure to improve with standard anti-pneumococcal antibiotics
(4) unsuspected HIV infection
(a) consider if risk factors exist or lymphocyte count < 1,000
b) development of a complication of pneumonia
(1) empyema
(2) abscess
(3) metastatic infection
c) unusual pathogens:
(1) Tularemia
(2) Coxiella burnetii
(3) M. Tuberculosis
(4) Psittacosis
(5) endemic fungal infections
(6) Nocardia
(7) Actinomyces
(8) Hantavirus
d) non-infectious diseases:
(1) pulmonary embolus
(2) bronchogenic carcinoma
(3) Wegener's granulomatosis
(4) eosinophilic pneumonia
(5) bronchiolitis obliterans organizing pneumonia
3. clinical approach:
a) bronchoscopy
(1) usually the initial test
b) open lung biopsy
(1) reserved for very ill patients with a negative bronchoscopy
c) serology - usually only useful after-the-fact to determine pneumonia causes for epidemiologic purposes
(1) cold agglutins
(2) Legionella
(3) viruses
(4) fungi
(5) Chlamydia
 
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