Clinical Analysis of Sputum Gram Stains and Cultures to Improve the Quality of Sputum Cultures

Abstract

Background: Sputum Gram stains and cultures are standard tests for the diagnosis of lower respiratory tract infections. Analysis reports of the sputum quality are scarce in relation to cultures as well as clinical diagnosis.Methods: A total of 1,523 sputum specimens, requested for culture, were evaluated for their quality using the modified Murray–Washington (MW) grouping system in association with the culture results. The clinical diagnosis was investigated for the culture positive cases.Results: There was a significant difference in bacterial growth (odds ratio, 2.01; P=0.0164) and diagnosis of pneumonia (odds ratio, 4.18; P=0.002) between the acceptable groups (groups 4–5) and the unacceptable groups (groups 1–3). However, one-quarter did not belong to the current MW group. More than half of the sputum cultures were in group 6, with the lowest positive rate (18.0%). Overall, 10% of the sputum cultures were related to a clinical diagnosis of pneumonia.Conclusions: The MW grouping system should be revised, because one-quarter did not belong to the current group. Further evaluation of group 6 will be needed. Improvement of sputum cultures is required to enhance the diagnosis of pneumonia.