Usually, the presence of bacteria in a patient's body fluid, especially blood, is determined using blood culture vials. A small quantity of blood is injected through an enclosing rubber septum into a sterile sample vial containing a culture medium. The vial is incubated at normal human body temperature and monitored for bacterial growth. Common visual inspection involves monitoring the turbidity of the liquid suspension. Known instrumental methods detect changes in the CO.sub.2 content of the culture vials, which is a metabolic by-product of the bacterial growth. Monitoring the CO.sub.2 content can be accomplished by methods well established in the art, such as radiochemical, infrared absorption at a spectral line characteristic of CO.sub.2, or pressure/vacuum measurement techniques such as those disclosed in Ahnell U.S. Pat. No. 4,152,213.
Recently, non-invasive methods have been developed involving the optical interrogation of chemical sensors disposed inside a sample vial that utilize colorimetric or fluorometric spectroscopic techniques. Some of these methods have also implemented remote sensing of multiple sample sites via optical fibers and switches. Additional non-invasive optical methods have been devised which rely on properties inherent in the liquid suspension and do not require the use of a chemical sensor; these include automated techniques for scattered photon migration measurements.
Typically, when using these non-invasive techniques, the sample vial must be agitated. Since it is both cost effective and time efficient to process samples in a batch, equipment must therefore be provided that agitates a large number of vials. Agitation, however, requires that the structure holding the vials moves relative to a stationary reference frame, and it is usually preferable to mount electronics and other equipment within the stationary portion of the system, not on the moving portion. This results in systems where both electrical cables and/or optical fibers must be designed to permit this relative motion by allowing sufficient excess at an appropriate point in the system. There remains a need, however, to permit a plurality of sample vials to be agitated while also permitting the interrogation of each vial by an optical fiber. It is accordingly an object of the present invention to provide an agitating rack and an optical excitation/detection system for transmitting electromagnetic energy to each sample vial in the rack and for receiving electromagnetic energy from each sample.