Diagnosis of Walking Pneumonia
Walking pneumonia (Mycoplasma pneumoniae pneumonia) is diagnosed by combining clinical features—specifically acute cough plus at least one additional finding (new focal chest signs, dyspnea, tachypnea, or fever >4 days)—with mandatory chest radiograph confirmation showing a pulmonary infiltrate. 1, 2
Essential Clinical Criteria
Acute cough is the mandatory symptom that must be present. 1 You then need at least one of the following:
Walking pneumonia typically presents with gradual onset of nonproductive cough, sore throat, and fever—distinguishing it from more acute bacterial pneumonias. 3 However, physical examination alone is neither sensitive nor specific for detecting pneumonia, with only 39% of patients with focal auscultatory abnormalities actually having pneumonia. 4, 1
Mandatory Radiographic Confirmation
A chest radiograph demonstrating a new or progressive infiltrate is required for definitive diagnosis—clinical features and physical examination alone are insufficient. 4, 1, 2 This is critical because chest radiography is necessary to differentiate pneumonia from acute bronchitis, which does not require antibiotics. 4, 2
Walking pneumonia characteristically shows interstitial infiltrates, patchy infiltrates, plate-like atelectasis, nodular infiltration, or hilar adenopathy on imaging. 3 If the initial chest radiograph is negative but clinical suspicion remains high, treat presumptively with antibiotics and repeat imaging in 24-48 hours. 4, 1
Pulse Oximetry Screening
All patients should be screened by pulse oximetry, which may suggest both the presence of pneumonia in patients without obvious signs and detect unsuspected hypoxemia. 4, 1
Critical Diagnostic Pitfalls
Do not diagnose pneumonia based solely on purulent sputum, fever, and leukocytosis without radiographic infiltrate—these findings have only 69% sensitivity and 75% specificity even when combined and can occur with colonization or tracheobronchitis. 1, 5 If these clinical features are present WITHOUT a new lung infiltrate, consider nosocomial tracheobronchitis instead. 1
Physical examination detecting rales or bronchial breath sounds is less sensitive and specific than chest radiographs, so never rely on examination alone. 4, 2
Additional Diagnostic Considerations
C-reactive protein (CRP) >50 mg/mL increases the probability of pneumonia, though its additional diagnostic value beyond history and physical examination requires further validation. 1 Blood cultures have high specificity when positive but sensitivity less than 25%, so negative cultures do not rule out pneumonia. 5
The combination of fever, absence of upper respiratory tract symptoms, dyspnea/tachypnea, and abnormal chest signs provides the strongest clinical prediction for pneumonia. 1