Diagnostic Considerations

Remember that the most prevalent causative organism in bacterial pneumonia is pneumococcus regardless of the host. Empiric therapy must be selected with this organism in mind.

Because the episode of aspiration is usually not witnessed, the diagnosis is inferred when a patient at risk of aspiration develops evidence of a radiographic infiltrate in characteristic anatomic pulmonary locations or bronchopulmonary segments.

Always consider the possibility of Legionella infection, because delayed treatment significantly increases mortality.

Despite the frequency of pneumonia and the large body of research and literature surrounding it, controversy remains regarding certain aspects of the evaluation and management of pneumonia. Much emphasis has been placed on the utility of diagnostic testing versus the role of empiric treatment. The following three aspects of disease are important in the management of pneumonia, in which diagnostic testing can play a pivotal role:

Determining the presence of pneumonia
Assessing disease severity at the time of presentation
Identifying the causative agent

Distinguishing pneumonia from other pulmonary pathologies, such as acute COPD or asthma exacerbation, can often present a significant challenge, particularly in patients with these underlying lung diseases. C-reactive protein (CRP) and procalcitonin values may help in distinguishing infectious pneumonia from noninfectious underlying disease exacerbations.^[52]

Differentiation between CAP, healthcare-associated pneumonia (HCAP), hospital-acquired pneumonia (HAP), and other pulmonary pathology at presentation is important for several reasons, but primarily because the varying pathogens implicated in each category dictate the empiric therapy likely to be most useful.^[3]

In children, the following conditions should also be taken into consideration:

Differential Diagnoses

Workup

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Media Gallery

Bacterial pneumonia. Radiographic images in a patient with right upper lobe pneumonia. Note the increased anteroposterior chest diameter, which is suggestive of chronic obstructive pulmonary disease (COPD).
Bacterial pneumonia. Radiographic images in a patient with bilateral lower lobe pneumonia. Note the spine sign, or loss of progression of radiolucency of the vertebral bodies
Bacterial pneumonia. Radiographic images in a patient with early right middle lobe pneumonia.
A 53-year-old patient with severe Legionella pneumonia. Chest radiograph shows dense consolidation in both lower lobes.
A 40-year-old patient with Chlamydia pneumonia. Chest radiograph shows multifocal, patchy consolidation in the right upper, middle, and lower lobes.
A 38-year-old patient with Mycoplasma pneumonia. Chest radiograph shows a vague, ill-defined opacity in the left lower lobe.
Chest computed tomography scan shows ill-defined, airspace infiltrate in the left lower lobe.
Chest computed tomography scan in a 45-year-old patient with Chlamydia pneumonia shows a right upper-lobe infiltrate.
Image in a 49-year-old woman with pneumococcal pneumonia. The chest radiograph reveals a left lower lobe opacity with pleural effusion.
Image in a 48-year-old patient with Haemophilus influenzae pneumonia. The chest radiograph shows bilateral opacities with a predominantly peripheral distribution.
Image in a 49-year-old patient with pneumococcal pneumonia. This chest CT shows a left upper lobe opacity extending to the periphery.
Image in a 50-year-old patient with Haemophilus influenzae pneumonia. The chest CT shows a very dense round area of consolidation adjacent to the pleura in the left lower lobe.
(Left) Gram stain demonstrating gram-positive cocci in pairs and chains and (right) culture positive for Streptococcus pneumoniae.
Gram stain showing Streptococcus pneumoniae.
Gram stain showing Haemophilus influenzae.
Gram stain showing Moraxella catarrhalis.
Sputum direct fluorescent antibody stain showing Legionella infection.
Chest radiograph in a patient with HIV infection, bilateral perihilar infiltrates, and Pneumocystis jiroveci pericarditis.
Chest radiograph in a patient with HIV infection and focal infiltrates due to tuberculosis.

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Table. Pathogen-Driven Antibiotic Choices^[3]

Table. Pathogen-Driven Antibiotic Choices ^[3]

Organism		First-Line Antimicrobials	Alternative Antimicrobials
Streptococcus pneumoniae
	Penicillin susceptible (MIC < 2 mcg/mL)	Penicillin G, amoxicillin	Macrolide, cephalosporin (oral or parenteral), clindamycin, doxycycline, respiratory fluoroquinolone
	Penicillin resistant (MIC ≥2 mcg/mL)	Agents chosen on the basis of sensitivity	Vancomycin, linezolid, high-dose amoxicillin (3 g/d with MIC ≤4 mcg/mL
Staphylococcus aureus
	Methicillin susceptible	Antistaphylococcal penicillin	Cefazolin, clindamycin
	Methicillin resistant	Vancomycin, linezolid	Trimethoprim- sulfamethoxazole
Haemophilus influenzae
	Non–beta-lactamase producing	Amoxicillin	Fluoroquinolone, doxycycline, azithromycin, clarithromycin
	Beta-lactamase producing	Second- or third-generation cephalosporin, amoxicillin/clavulanate	Fluoroquinolone, doxycycline, azithromycin, clarithromycin
Mycoplasma pneumoniae		Macrolide, tetracycline	Fluoroquinolone
Chlamydophila pneumoniae		Macrolide, tetracycline	Fluoroquinolone
Legionella species		Fluoroquinolone, azithromycin	Doxycycline
Chlamydophila psittaci		Tetracycline	Macrolide
Coxiella burnetii		Tetracycline	Macrolide
Francisella tularensis		Doxycycline	Gentamicin, streptomycin
Yersinia pestis		Streptomycin, gentamicin	Doxycycline, fluoroquinolone
Bacillus anthracis (inhalational)		Ciprofloxacin, levofloxacin, doxycycline	Other fluoroquinolones, beta-lactam (if susceptible), rifampin, clindamycin, chloramphenicol
Enterobacteriaceae		Third-generation cephalosporin, carbapenem	Beta-lactam/beta-lactamase inhibitor, fluoroquinolone
Pseudomonas aeruginosa		Antipseudomonal beta-lactam plus ciprofloxacin, levofloxacin, or aminoglycoside	Aminoglycoside plus ciprofloxacin or levofloxacin
Bordetella pertussis		Macrolide	Trimethoprim- sulfamethoxazole
Anaerobe (aspiration)		Beta-lactam/beta-lactamase inhibitor, clindamycin	Carbapenem
MIC = Minimal inhibitory concentration.

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Author

Justina Gamache, MD Resident Physician, Department of Internal Medicine, Olive View-UCLA Medical Center

Disclosure: Nothing to disclose.

Coauthor(s)

Annie Harrington, MD Fellow in Pulmonary and Critical Care Medicine, Cedars-Sinai Medical Center

Annie Harrington, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Chest Physicians

Disclosure: Nothing to disclose.

Nader Kamangar, MD, FACP, FCCP, FCCM Professor of Clinical Medicine, University of California, Los Angeles, David Geffen School of Medicine; Chief, Division of Pulmonary and Critical Care Medicine, Vice-Chair, Department of Medicine, Olive View-UCLA Medical Center

Nader Kamangar, MD, FACP, FCCP, FCCM is a member of the following medical societies: Academy of Persian Physicians, American Academy of Sleep Medicine, American Association for Bronchology and Interventional Pulmonology, American College of Chest Physicians, American College of Critical Care Medicine, American College of Physicians, American Lung Association, American Medical Association, American Thoracic Society, Association of Pulmonary and Critical Care Medicine Program Directors, Association of Specialty Professors, California Sleep Society, California Thoracic Society, Clerkship Directors in Internal Medicine, Society of Critical Care Medicine, Trudeau Society of Los Angeles, World Association for Bronchology and Interventional Pulmonology

Disclosure: Nothing to disclose.

Chief Editor

Guy W Soo Hoo, MD, MPH Professor of Clinical Medicine, University of California, Los Angeles, David Geffen School of Medicine; Director, Medical Intensive Care Unit, Chief, Pulmonary, Critical Care and Sleep Section, West Los Angeles VA Healthcare Center, Veteran Affairs Greater Los Angeles Healthcare System

Guy W Soo Hoo, MD, MPH is a member of the following medical societies: American Association for Respiratory Care, American College of Chest Physicians, American College of Physicians, American Thoracic Society, California Thoracic Society, Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Acknowledgements

Paul Blackburn, DO, FACOEP, FACEP Attending Physician, Department of Emergency Medicine, Maricopa Medical Center

Paul Blackburn, DO, FACOEP, FACEP is a member of the following medical societies: American College of Emergency Physicians, American College of Osteopathic Emergency Physicians, American Medical Association, and Arizona Medical Association