INFECTIOUS DISEASES
Common organisms
causing pneumonia
|
Young,
healthy adult |
S. pneumoniae, Mycoplasma, Chlamydia
pneumoniae, respiratory viruses |
|
Elderly |
S. pneumoniae, influenza virus, M. tuberculosis |
|
Debilitated |
S. pneumoniae, influenza virus, M. tuberculosis,
gram negative bacilli |
|
Hospitalized |
Oral flora, S.
aureus, gram negative bacilli, Legionella |
Note that S.
pneumoniae is responsible for 50-75% of community acquired pneumonias
(CAP), while gram-negatives cause > 80% of nosocomial pneumonias.
Evaluation of
pneumonia
1.
History
a.
Pre-disposing
factors
i.
COPD: H.
influenzae, S. pneumoniae, Legionella, Moraxella
catarrhalis
ii.
Recent seizures:
aspiration pneumonia (mixed anaerobes)
iii.
Compromized
host: Pneumocystis carinii, CMV, Legionella, gram-negatives,
fungi, MAC
iv.
Alcoholics:
aspiration, S. pneumoniae, Klebsiella, gram-negatives, H.
influenzae
v.
Diabetes
mellitus: gram-negatives, M. tuberculosis
vi.
Sickle cell: S.
pneumoniae, Mycoplasma
b.
Symptoms
i.
S.
pneumoniae – abrupt onset
with fever, shaking chills, rust-colored sputum.
ii.
Mycoplasma – insidious onset with gradual onset of
fever, hacking cough, scant sputum.
iii.
Elderly
patients initially may have only minimal symptoms.
iv.
Viral
pneumonias – generalized body aches, malaise, dry, non-productive cough.
2.
Diagnosis
a.
Attempt to
obtain sputum for Gram stain and culture – often inadequate due to many false
positive results (oral flora contamination) and false negative results. Aerosol induction with hypertonic saline may
increase diagnostic yield.
b.
PA and lateral
CXR – also use to rule out empyema, pneumothorax, abscess.
i.
S.
pneumoniae – segmental or
lobar infiltrate
ii.
Mycoplasma – patchy infiltrates; may suggest a more
serious infection than the patient’s appearance or physical exam.
iii.
Viral – hazy
infiltrates
iv.
Diffuse
infiltrates – Legionella, Mycoplasma, viral pneumonia, P.
carinii, aspiration pneumonia, hypersensitivity pneumonitis, aspergillosis
c.
CBC
d.
Blood cultures
– positive in 20% of patients with pneumococcal pneumonia.
e.
ABG – PaO2
of 60 mmHg on room air is criteria for hospital admission.
Initial
antibiotic treatment of pneumonia
(taken from Sanford Guide to Antimicrobial Therapy 2001 edition)
|
Patient type |
Suspected pathogens |
Initial coverage |
|
Outpatient CAP,
< 60 yo, otherwise healthy |
S. pneumoniae, Mycoplasma, Chlamydia, H.
influenzae, viral |
Macrolide
(azithromycin, clarithromycin) or a fluoroquinolone or doxycycline |
|
Outpatient CAP,
> 60 yo or with comorbidity (COPD, CHF, DM, liver disease, renal failure,
alcoholic) |
S. pneumoniae, H. influenzae, aerobic gram
negative rods, S. aureus |
Fluoroquinolone
or second generation cephalosporin (cefuroxime) plus macrolide if atypicals
suspected |
|
CAP requiring
hospitalization |
S. pneumoniae, H. influenzae, anaerobes, aerobic
gram-negatives, Chlamydia |
Third generation
cephalosporin (cefotaxime, ceftriaxone) plus a macrolide or a fluoroquinolone
alone |
|
Severe CAP
requiring ICU care |
S. pneumoniae, H. influenzae, aerobic gram-negatives,
Mycoplasma, Legionella |
Third generation
cephalosporin or b-lactam / b-lactamase inhibitor
(Zosyn, Unasyn, Augmentin) plus either a fluoroquinolone or a macrolide |
|
Nosocomial
pneumonia – patient hospitalized > 48 hours |
S. pneumoniae, Gram-negative rods (Pseudomonas, Legionella,
Acinetobacter), S. aureus |
Imipenem or
meropenem or aminoglycoside plus either an anti-pseudomonal penicillin
(piperacillin, ticarcillin) or b-lactam / b-lactamase inhibitor
± clindamycin |
Common organisms
causing meningitis and recommended treatment
|
Patient Type |
Suspected pathogens |
Initial coverage |
|
Immunocompetent |
|
|
|
< 3 months |
S. agalactiae, E. coli, or Listeria |
Ampicillin plus
third generation cephalosporin (cefotaxime) |
|
3 mo – 18 yo |
N.
meningitidis, S.
pneumoniae, or H. influenzae |
Third generation
cephalosporin (cefotaxime or ceftriaxone) |
|
18 – 50 yo |
S. pneumoniae or N. meningitidis |
Third generation
cephalosporin ± ampicillin ± vancomycin |
|
> 50 yo |
S. pneumoniae, Listeria, or gram-negative rods |
Ampicillin plus
third generation cephalosporin ± vancomycin |
|
Impaired cellular
immunity |
Listeria or gram-negative rods |
Ampicillin plus
ceftazidime |
|
With head trauma,
neuro-surgery, CSF shunt |
S. aureus, S. pneumoniae, coag-negative Staphylococcus,
gram-negative rods, P. aeruginosa |
Vancomycin plus
ceftazidime |
(table taken from
Sanford Guide to Antimicrobial Therapy 2001 edition, Ferri, and NEJM
1997;336:708-716
Evaluation of
meningitis
1.
History
a.
Predisposing
factors
i.
S.
pneumoniae – common in
adults, elderly; predisposing factors include blunt head trauma, otitis media,
pneumonia, sickle cell, CSF leaks; mortality is 30%.
ii.
N.
meningitidis – complement
deficiencies
iii.
H.
influenzae – usually seen
in preschool age children; predisposing factors in adults include head trauma,
otitis media, and sinusitis.
iv.
S. aureus – diabetics, patients with S. aureus
pneumonia, cancer.
v.
Enteroviruses
(coxsackievirus, echovirus) are the most common cause of viral meningitis.
vi.
Suspect
tuberculosis meningitis in a patient with unrelenting headache, malaise, low
grade fever with lymphocytic pleocytosis, and mildly decreased CSF glucose.
b.
Symptoms and
physical exam
i.
Classic
presentation is fever, headache, lethargy, confusion, nuchal rigidity. A recent review (JAMA 1999;282:175-181)
reported that 95% of patients will have at least two symptoms from the triad of
fever, neck stiffness, and altered mental status/headache, 99-100% will have at
least one of these three symptoms.
However, these symptoms may not always be present in infants,
immunocompromised, and the elderly.
(1)
Fever – 85%
sensitive
(2)
Neck stiffness
– 70% sensitive
(3)
Altered mental
status – 67% sensitive; more commonly seen in bacterial meningitis
ii.
Meningeal
signs
(1)
Kernig’s
sign: pain in the lower
back or posterior thigh when knee is extended while patient is lying in supine
position and hip is flexed at a right angle.
(2)
Brudzinski’s
sign: rapid neck flexion à involuntary knee flexion in a supine
position.
(3)
These signs
are not very sensitive but are very specific for meningitis
iii.
Infants may
have a bulging fontanelle, poor feeding, vomiting, and respiratory distress.
iv.
Petechial-purpuric
rashes (trunk, lower extremities, mucous membranes, conjunctiva) are suggestive
of meningococcal meningitis; also seen in viral and other bacterial meningitis.
v.
Seizures and
papilledema are unusual.
2.
Diagnosis
a.
CBC –
elevated WBC with left shift.
b.
Blood cultures
– if patient is very ill, start antibiotics before cultures are obtained.
c.
Coagulation
panel and fibrin split products – rule out DIC in patients with petechiae,
purpura, and hypotension.
d.
CSF studies
i.
Tube 1 =
protein, glucose, cell count and differential
ii.
Tube 2 = Gram
stain, cultures
iii.
Tube 3 = other
tests (EV-PCR, etc.)
iv.
Tube 4 = cell
count and differential, (AFB smear if suspected)
CSF findings in
meningitis and various CNS abnormalities
|
|
Appearance |
Glc (mg/dl) |
Protein (mg/dl) |
Cell count ( / mm3) and type |
Pressure (mmHg) |
|
Normal adult |
Clear |
50-80 |
20-45 |
0-5, 100% lymphs |
100-200 |
|
Viral meningitis |
Clear / cloudy |
Normal |
|
(< 1000),
mostly lymphs |
Nl / |
|
Acute bacterial
meningitis |
Cloudy |
¯ (< 40) |
|
(several thousand), predominantly PMNs |
|
|
Tuberculous
meningitis |
Cloudy |
¯ |
|
PMNs (early) lymphs
(late) |
|
|
Fungal meningitis |
Clear / cloudy |
¯ |
|
monocytes |
|
|
Neurosyphillis |
Clear / cloudy |
Normal |
|
monocytes |
Nl / |
|
Guillain-Barre
syndrome |
Clear / cloudy |
Normal |
|
Normal / , monocytes |
Normal |
|
Neoplasm |
Clear / xanthochromic |
Nl / ¯ |
Nl / |
Normal / , lymphs |
|
|
Hemorrhage |
Bloody / xanthochromic |
Nl / ¯ |
|
RBCs |
|
3.
Treatment
a.
See table on
previous page for antibiotics recommended for empiric therapy (taken from
Sanford Guide to Antimicrobial Therapy 2001 edition, Ferri, and NEJM
1997;336:708-716).
b.
Dexamethasone
i.
Mechanism of
action in meningitis
(1)
Inhibits
synthesis of inflammatory cytokines (IL-1, TNF) that induce meningeal
inflammation.
(2)
Stabilizes
blood-brain barrier.
(3)
Decreases CSF
outflow resistance.
(4)
Improves
indices of inflammation in CSF when given before first dose of antibiotics.
(5)
Reduces
sensorineural hearing loss and other neurologic sequelae in meningitis
secondary to H. influenzae.
(6)
Reduces
mortality and adverse neurologic sequelae in meningitis secondary to S.
pneumoniae.
ii.
Recommendations
for use
(1)
Treatment of H.
influenzae meningitis in previously healthy infants and children > 2
mo. Give for the first 4 days of
antimicrobial therapy.
(2)
Treatment of S.
pneumoniae meningitis in children within the first 2 days of the illness.
(3)
Tuberculous
meningitis.
(4)
Any adult with
bacterial meningitis and significant change in sensorium.
c.
Repeat lumbar
punctue after 24-36 hours of antibiotic therapy to verify eradication of the
organism.
d.
Prophylaxis
i.
Indications include
contact with patients who have N. meningitidis or H. influenzae
meningitis, including members of the same household and those with close
contact to the index case, including hospital personnel. Consider prophylaxis of contacts at day
care, school, or chronic care facilities on an individual basis.
ii.
Rifampin is
commonly used for prophylaxis of both N. meningitidis and H.
influenzae meningitis.