Pneumonia

most common pathogens

The following pathogens represent the most common causes of pneumonia in different populations:

bacterial pathogens

Streptococcus pneumoniae (pneumococcus) is the most common cause of community-acquired pneumonia. It colonizes the oropharynx of up to 25% of healthy adults. Increased predisposition is seen in people with alcoholism, chronic lung disease, renal failure, sickle cell disease, prior splenectomy, hematologic malignancy, and HIV infection. Lobar consolidation with air bronchograms is typically seen by the 2nd or 3rd day of illness. In most areas of the world, penicillin G is the treatment of choice, with cephalosporins or vancomycin indicated depending on regional sensitivity patterns.

Staphylococcus aureus accounts for 2-5% of community acquired pneumonias, 11% of hospital pneumonias, and up to 26% of pneumonias following viral infection.

Haemophilus influenzae, a gram-negative coccobacillus often present in the upper respiratory tract, is especially important in people with COPD. Even though pathologic involvement therefore depends on isolation by bronchoscopy or other methods, if seen in a sputum sample, treatment should begin with ampicillin plus a beta-lactamase inhibitor, or a 2nd- or 3rd-generation cephalosporin.

Gram-negative bacilli are increasingly important lung pathogens due to use of potent antibiotics and intensive care units. They are ubiquitious throughout hospitals, contaminating equipment and instruments, and are a major source of nosocomial pneumonia. Important pathogens include klebsiella pneumoniae, Escherichia coli, Pseudomonas spp, Legionella

Other bacteria include mycoplasmal and chlamydial pneumonias

• Francisella tularensis
• Yersinia pestis
• Rhodococcus equi

viral pathogens

In children, viruses are the most common cause of pneumonia, with respiratory synctial virus being the most common pathogen.

Respiratory viral infection is usually limited to the upper respiratory tract, and only a small proportion of infected adults develop pneumonia.

Viral causes include:

• influenza (older adults, patients with chronic heart, lung, or kidney disease, last trimester pregnancy)
• varicella
• measles
• CMV (immunosuppressed patients)
• hantavirus

Influenza-induced necrosis of epithelial cells predisposes to bacterial colonization, and S. pneumoniae, S. aureus, and H. influenzae pneumonias are the most common concomitant infections.

History

Respiratory symptoms of pneumonia include:

• cough
  • persistent, hacking - Mycoplasma
• sputum production
• dyspnea (shortness of breath)
• chest pain, especially pleuritic
• fever
• malaise
• absence of rhinorrhea or sore throat

A history of rhinitis or pharyngitis suggests respiratory virus, Mycoplasma, or Chlamydia. Abrupt onset of myalgia, arthralgia, headache, and fever are commonly seen in influenza virus infection.

Abrupt onset of myalgias, arthralgia, headache, and fever suggest influenza or mycoplasma.

Duration of symptoms is a critical piece of information:

• pneumococcal, mycoplasma, or virual or viral disease is usually acute, with symptoms lasting for hours or days.
• Symptoms lasting 10 days or longer are rarely caused by common bacterial pathogens and should raise suspicion of mycobacterium, fungal, or anaerobic pneumonia, and/or the presence of underlying disease.

Review of symptoms

• diarrhea - suggests Legionella
• altered mental status - ?meningitis

past medical history

• asthma
• dementia
• immunosupression

Physical Exam

Most people with pneumonia have cough, fever, pleuritic chest pain, foul sputum, tachycardia, and tachypnea.

Tuberculosis can lead to high fever with few other symptoms.

Foul breath suggests anaerobes and/or lung abscess.

Confusion should immediately point to meningeal complications, or can simply represent delirium in the elderly.

Brown currant jelly sputum suggests Klebsiella

The respiratory exam can show evidence of consolidation via the following:

• percussion dullness
• bronchial breath sounds
• crackles
• increased fremitus
• whispered pectoriloquy

Increasing tachypnea, cyanosis, and use of accessory muscles for respiration suggests serious illness. Foul breath suggests anaerobic infection, ie lung abscess.

If a person presents with abrupt onset of chills, cough, pleuritic chest pain, rusty or yellow sputum, and shortness of breath, and exam shows tachypnea shows even miminal signs of pulmonary inflammation, presumptive diagnosis of bacterial pneumonia should be made, sputum should be examined, and apropriate therapy should be begun.

Emperic therapy without sputum examination is often successful, but increases in antibiotic resistance and occasional misdiagnosis, leading to increased risk of morbidity and death, mean that sputum should be Gram-stained and examined immediately.

Diagnosis is made in about 20% of patients.

Lab Investigations

blood tests

• CBCD: usual elevated white cell count, with left shift; higher for bacterial infection
• lytes
• urea, sCR
• troponin/CK
• AST, ALT, ALP,
• bili: modest increases in conjugated bilirubin are seen in many bacterial infections
• C-reactive protein: monitoring severity of infection and treatment response
• blood culture: will be positive for 20-30% of people with bacterial pneumonia.

nasopharyngeal swab: influenza, parainfluenza, metapneumovirus, RSV, adenovirus

sputum smear and culture: must be done carefully to avoid contamination by oropharyngeal flora. Both false negatives and false positives are common and should be interpreted carefully.

• gram stains
• Gomori's Methenamine Silver (GMS stain)
• PAS/diastase stain
• Ziehl-Neelsen stain for mycobacteria: should be done unless diagnosis of acute bacterial pneumonia is clear
• viral inclusions

other tests:

• urinalysis
• tuberculin skin test
• lumbar puncture should be done in patients with penumonia and confusion to rule out meningitis
• mycoplasma IgM
• tissue biopsy can be very helpful, but its invasiveness is an important consideration.

Diagnostic Imaging

Suspect pneumonia in children with fever, cough, retractions, and tachypnea; a chest X-ray is not necessary in the outpatient setting (Harris et al, 2011).

chest X ray

Chest X-rays need to be examined in the context of clinical data to successfully lead to diagnosis. A negative chest X ray can never rule out acute pneumonia if signs and symptoms are strongly suggestive.

Hypersensitivity pneumonia, early milliary TB, or early PJP can result in symptoms in the absence of radiographic findings.

Findings on a chest X ray can include:

• homogenous parenchymal consolidation involving one or more lobe
• pleural effusions (S. pneumoniae or M. tuberculosis)
• bilateral infiltration (Mycoplasma)
• cavitation: suggests necrosis (TB, Staph, GNRs, anaerobes, fungi, or Pneumocystis jirovecci)

Radiologic findings of lobar pneumonias slowly clear, suggesting 6 week interval for followup.

Immediate Treatments

As with any patient, it is important to begin by treating the vitals, or ABCs, of the patient. This includes, as necessary:

• oxygen administration and monitoring of saturation
• positioning
• IV access
• salbutamol/Ventolin

Community-acquired Pneumonia

external resources:

• Infectious Disease Society of America
• American Thoracic Society

Empiric treatment of CAP is often successful, but using broad-spectrum antibiotics can lead to increased resistance and occasional misdiagnosis.

The Americal Academy of Emergency Physicians now recommends against routine blood cultures and early antiobiotics for presumptive CAP, before definitive clinical diagnosis is made (Nazarian et al, 2009).

Previously healthy

No antibiotics within past three months:

• amoxicillin/penicillin
• macrolide (though resistance increasing)
• doxycyline
• fluoroquinolone

antibiotics with past three months:

• fluoroquinolone
• macrolide plus amoxocillin
• macrolide plus amoxocillin-clavulin

co-morbidities (COPD, diabetes, renal failure, CHF, malignancy)

no antibiotics within past three months:

• macrolide
• fluoroquinolone

antibiotics within 3 months:

• fluoroquinolone
• macrolide plus beta-lactam

suspected aspiration (oral anaerobes)

• amoxocillin-clavulanate
• clindamycin

A small study has recommended the addition of dexamethasone to the treatment of hospitalized patients, as this appears to decrease length of stay (Meijvis et al, 2011).

Nosocomial Pneumonia

Patients who develop pneumonia from a health care setitng are at risk from a more dangerous pathogen, as described above. Antibiotics should be given according to likely pathogens involved:

Pseudomonas

• ceftazedime
• piperacillin-tazobactam

MRSA:

• vancomycin plus rifampicin (Jung et al, 2010).

further gram -ve coverage

• ciprofloxacin
• aminoglycoside (gentamicin, tobramycin) plus fluroquinolone
• aminoglycoside (gentamicin, tobramycin) plus macrolide (azithromycin)

suspect aspiration (oral anerobes)

• clindamycin
• metronidazole

ventilator-associated pneumonia

• vancomycin/linezolid + ciprofloxacin/ceftazidime
• cefepime and gentamycin
• meropenem

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