**5. Interference of released antimicrobials with diagnostic tests**

Concern has been raised that release of antimicrobials into the lumen of the catheter might interfere with diagnosis of ventriculitis by inhibiting or killing any bacteria before they can be grown on culture. This concern was reinforced by a study by Stevens et al. [56] who suggested, on the basis of in vitro studies, that it might be justified. However, the methods used did not simulate events encountered in practice, and the issue was revisited [57]. In this study, both the commercially available antimicrobially impregnated catheters (Bactiseal and Ventriclear) were included, and the methods were designed to mimic their use in an EVD system, with bacterial challenge and CSF sampling modelled on clinical events and procedures. The study found that, in samples taken on Day 1 of "EVD" bacterial viability was significantly reduced by the antimicrobial release, which occurred as a burst effect only in the first 24 hr. After this, no reduction was seen. It is unlikely that CSF sampling would be required as early as the first 24 hr. of EVD, and the conclusion was that no clinically relevant interference with diagnosis was found.
