Limited value of chest radiography in predicting aetiology of lower respiratory tract infection in general practice

Background: In patients with lower respiratory tract infection (LRTI), changes on chest radiography are rare but poorly characterised, especially in general practice. Aim: To describe the range of findings on chest radiographs and the associations between these findings and the aetiology of LRTI. Design of study: A prospective observational study. Setting: General practices in the Leiden region, The Netherlands. Method: Adult patients with a defined LRTI were included. Standard medical history and physical examination were performe̊d. Sputum, blood, and throat swabs were collected for diagnostic tests. Chest X-ray findings were assessed in relation to the aetiology. Results: An abnormality on the chest X-ray was observed in 72 (55%) patients. Forty-five patients (35%) had changes due to infection, and 26 (20%) due to pneumonia. Pathogens were detected in 84 patients (33 single bacterial, 43 single viral, and 8 dual). Twelve (29%) patients with a bacterial infection (including dual infections) compared to four (9%) patients with viral infection had pneumonia on the chest X-ray (odds ratio [OR] = 4.0; 95% confidence interval [CI] = 1.2 to 13.8). Using the presence of pneumonia on chest X-ray as a test to predict a bacterial infection, the positive predictive value and the negative predictive value were 75% (CI = 48 to 93%) and 57% (CI = 45 to 69%), respectively. Conclusion: Pneumonia on the chest X-ray was found more frequently in patients with a bacterial infection than in patients with a viral infection. However, the sensitivity and the specificity are such that pneumonia on the chest X-ray is not a reliable test to discriminate between bacterial and non-bacterial LRTI in the general practice setting.

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