Answer: a, b, c, d Although the classic detection of infection based on clinical signs of infection and bacterial culture remain the most common clinical tools, increasing reliance has been placed on assays that do not employ cultural data. Specifically, the antibody and cytokine host responses are being intensely examined and extremely sensitive amplified assays that rely on antigen, antibody or microbial DNA detection are employed in the clinical setting. Enzyme-linked immunosorbent assay (ELISA) is a rapid, antigen-based, immunologic assay that can be used for both antigen and antibody detection, for determination of antibody titer, as well as for screening for monoclonal antibody production. Transblot techniques are being used increasingly in the clinical setting. These include southern, northern, and western immunotransblot techniques used to detect DNA, RNA, or proteins, respectively. The polymerase chain reaction (PCR) is being used in some centers as a sensitive assay to detect small amounts of microbial DNA. This technique involves extraction of the DNA from the test sample with in vitro amplification through repeated nucleic acid denaturing and polymerization so that the gene copy number increases exponentially. This marked amplification of the gene copy number results in extremely sensitive tests which can detect infection at its early stages. Clinically, these detection methods are being used to detect a wide variety of infectious agents including CMV and HIV. Furthermore, preliminary investigations into possible detection of fungal pathogens are underway