I appreciate the comments of Drs Sakoulas, Degirolami, and Gold on my study.1 Their case presentation supports a major finding of my study that prior MRSA colonization or infection is a strong predictor of subsequent methicillin resistance in S aureus infections. In addition, they make an extremely important point about clinical decision making and the interpretation of diagnostic tests. Diagnostic tests must be interpreted in light of the pretest likelihood of a particular condition. In their case presentation, the pretest likelihood of methicillin resistance in the second S aureus bacteremia was very high. Thus, finding oxacillin (or methicillin) susceptibility leads to a lower but still high posttest probability of methicillin resistance. Further testing was called for and revealed the presence of the mecA gene.
Roghmann M. Methicillin-Susceptible Staphylococcus aureus: Believe It, or Not—Reply. Arch Intern Med. 2001;161(9):1238. doi: