Diagnostic Considerations
Patients diagnosed with Legionella pneumonia are not usually coinfected with other organisms (eg, pneumococcal species). The differential diagnoses include other atypical pathogens (eg, Mycoplasma, psittacosis), Chlamydophila pneumoniae, tularemia, and Coxiella burnetii.L pneumophila bacterium represents a definite pathogen; therefore, its isolation always indicates infection.
Differentials in Legionnaires disease (LD) also include the following:
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Aspiration pneumonia
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Bacterial pneumonia
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Viral pneumonia
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Prostatitis
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Respiratory distress syndrome
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Septic shock
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Typical community-acquired pneumonias (CAPs)
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Atypical CAPs
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Severe CAP
Differentials
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This electron micrograph depicts an amoeba, Hartmannella vermiformis (orange), as it entraps a Legionella pneumophila bacterium (green) with an extended pseudopod. After it is ingested, the bacterium can survive as a symbiont within what then becomes its protozoan host. The amoeba then becomes a so-called "Trojan horse," since, by harboring the pathogenic bacterium, the amoeba can afford it protection. In fact, in times of adverse environmental conditions, the amoeba can metamorphose into a cystic stage, enabling it, and its symbiotic resident, to withstand the environmental stress. Image courtesy of the Centers for Disease Control and Prevention and Dr. Barry S Fields.
Tables
Diagnostic Predictors |
Diagnostic Eliminators |
Clinical Predictors
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Clinical Eliminators
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Laboratory Predictors b
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Laboratory Eliminators
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Legionnaire disease very likely if >3 predictors present |
Legionnaires disease very unlikely if < 3 predictors or >3 diagnostic eliminators present |
Abbreviations: CPK = creatinine phosphokinase test; CRP = C-reactive protein; ESR = erythrosedimentation rate. a Pulmonary symptoms: shortness of breath, cough, and so forth with fever and a new focal/segmental infiltrate on chest radiograph. b Otherwise unexplained. If finding is due to an existing disorder, it should not be used as a clinical predictor. |
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