Why oral antiseptic mouth rinsing before sputum collection cannot reduce contamination rate of mycobacterial culture in Burkina-Faso

Background Tuberculosis (TB) diagnosis by culture in most resource-limited settings is hampered by high contamination rate varying up to 31%. Reduction of oral microorganism loads by mouth rinse with antiseptic before sputum collection showed a reduction of contamination. Moreover, knowing the characteristic of residual contaminant microorganisms would be an asset to understand contamination issues. Objectives The aim of this study was to evaluate the effects of mouth rinsing with chlorhexidine on mycobacteria culture contaminations and to characterize morphologically the residual contaminants. Methods We consecutively included 158 patients in a TB center. Each of them supplied two sputa: The first before mouth rinse, and the second after 60sec of mouth rinsing with chlorhexidine (0.1%). Petroff method and Lowenstein-Jensen media were used for sputum decontamination and inoculation respectively. The contamination rates were compared, and the type of residual contaminants were characterized and compared. Results The contamination rate did not differ before and after the mouth rinse (respectively 58/150 (39 %) vs 61/150 (41 %), p=0.7). The major residual contaminants were Gram positive spore forming bacteria (94%). Conclusion Chlorhexidine mouth rinsing before sputum collection did not reduce mycobacterial culture contamination rate. This is probably due to spore forming bacteria, highlighted as major residual contaminants.