The two-tiered Quantitative Carrier Test (QCT) methodology was developed at the University of Ottawa (Canada) to improve upon the existing carrier test protocols in use in North America and elsewhere. The methods are designed to assess the microbicidal activities of chemicals for decontamination of medical devices and hard, non-porous environmental surfaces while better simulating field conditions.
The first tier of the test (QCT-1), which uses glass vials with a smooth surface, is meant as a screening tool. The volume of the test formulation is relatively high in this protocol and the use of a soil load in the test suspension is also optional. It is amenable for work with all major classes of human pathogens except viruses.
The second tier of the test (QCT-2) is more stringent for even closer simulation of field conditions that a disinfectant may encounter. It uses disks (0.7 mm thick with a diameter of 1 cm) of brushed stainless steel as representative hard, nonporous surfaces. The use of a soil load is mandatory in it. It is suited for work with all major classes of human pathogens, including viruses.
Both the tiers are designed as closed systems whereby no viable organisms are ‘lost’ during sample processing, thus allowing for precise and reproducible determinations of log10 determinations after exposure to the test formulation. The use of membrane filtration (except for viruses) enables the capture of all organisms in control and test samples while also permitting a better removal of potentially inhibitory residues of the test formulation.