Sputum colour for diagnosis of a bacterial infection in patients with acute cough

Abstract

Objective. Sputum colour plays an important role in the disease concepts for acute cough, both in the patients' and the doctors' view. However, it is unclear whether the sputum colour can be used for diagnosis of a bacterial infection. Design. Cross-sectional study. Setting. A total of 42 GP practices in Dusseldorf, Germany. Subjects. Sputum samples obtained from 241 patients suffering from an episode of acute cough seeing their doctor within a routine consultation. Main outcome measures. Relation of sputum colour and microbiological proof of bacterial infection defined as positive culture and at least a moderate number of leucocytes per low magnification field. Results. In 28 samples (12%) a bacterial infection was proven. Yellowish or greenish colour of the sputum sample and bacterial infection showed a significant correlation (p = 0.014, Fisher's exact test). The sensitivity of yellowish or greenish sputum used as a test for a bacterial infection was 0.79 (95% CI 0.63-0.94); the specificity was 0.46 (95% CI 0.038-0.53). The positive likelihood-ratio (+LR) was 1.46 (95% CI 1.17-1.85). Conclusions. The sputum colour of patients with acute cough and no underlying chronic lung disease does not imply therapeutic consequences such as prescription of antibiotics.