TABLE 2.11.

Differentiation of Classical Bacterial Pneumonia from Viral and Atypical Pneumonias^*

	Bacterial	Viral/Atypical
History	Precedent URI	Headache, malaise, URI, myalgias
Course	Often biphasic illness	Often monophasic
Onset	Sudden	Gradual
Temperature	High fever	Low-grade fever
Rigors	Common	Uncommon
Vital signs	Tachypnea, tachycardia	Usually normal
Pain	Pleuritic	Unusual
Chest examination	Crackles, signs of consolidation	Consolidation unusual
Pleural effusion	Common	Uncommon
Sputum	Productive, purulent, many PMNs, one dominant organism on Gram stain	Scant, no organisms; PMNs or mononuclear cells
ESR	Elevated	Usually normal
WBC count	Elevated; left shift	Often normal; predominant lymphocytes
Chest radiography	Lobar consolidation, round infiltrate, parapneumonic effusion; may be “bronchopneumonia”	Diffuse, bilateral, patchy, interstitial or bronchopneumonia; lower lobe involvement common; chest radiograph may look worse than patient's condition
Progression	May be rapid	Rapid if Legionella species, hantavirus, SARS, herpesvirus, adenovirus
Diagnosis	Blood, sputum, and pleural fluid specimens for culture; antigen detection possible; BAL if progressive	Viral, chlamydial culture or PCR detection; acute and convalescent titers; BAL if progressive

BAL, bronchoalveolar lavage; ESR, erythrocyte sedimentation rate; PMNs, polymorphonuclear neutrophils; SARS, severe acute respiratory syndrome; URI, upper respiratory tract infection; WBC, white blood cell.

^*Atypical pneumonias include Chlamydia pneumoniae, Mycoplasma pneumoniae, Legionella species (L. pneumophila, L. micdadei), Q fever, psittacosis.