True positive, true negative, and discordant (positive by a single method) results obtained by IDI-MRSA assay, GenoType MRSA Direct, and selective MRSA agars, with final resolved allocationa

ParameterNo. of specimens
True positive results
    Positive by two or more methods44517
    Positive by two molecular methods only72
    Discordant results resolved to be truly positive
        IDI-MRSA positive only2
        MRSA ID selective agar positive only1
True positive total (n = 78)53817
True negative results
    Negative by all methods484331
    Discordant results resolved to be truly negative
        IDI-MRSA positive only11
        GenoType MRSA Direct positive only3b
True negative total (n = 127)484435
  • a Resolution of the discordant results was done as described in Materials and Methods.

  • b All three samples were Genotype MRSA Direct positive and selective and nonselective agar negative. Two samples were IDI-MRSA negative, and one sample was IDI-MRSA inhibitory.