On the basis of these data, specific serological data as a surrogate marker for positive blood cul- tures have now been included in the Duke criteria. Thus, an anti phase I immunoglobulin G antibody titer 1:800 or a single blood culture positive for C burnetii should be a major criterion in the modified Duke schema.24 Serological tests and PCR-based testing for other diffi- cult-to-cultivate organisms such as Bartonella quintana or Tropheryma whippelii also have been discussed as future major criteria. At present, there are significant methodologi- cal problems associated with proposing antibody titers that are positive for Bartonella and Chlamydia species or PCR-based testing for T whippelii as a major criterion in the Duke schema. For example, IE caused by Bartonella and Chlamydia species often are indistinguishable in serological test results because Low sensitivity is a major limitation of PCR unless cardiac valvular tissue is available for testing.42 45 Few centers provide timely PCR-based testing for these rare causes of IE. Therefore, the inclusion of these assays as major criteria should be deferred until the serodiagnostic and PCR approaches can be standardized and validated in a sufficient number of cases of these rare types of IE, the aforementioned technical problems are resolved, and the availability of such assays becomes more widespread. The expansion of minor criteria to include elevated eryth- rocyte sedimentation rate or C-reactive protein, the presence of newly diagnosed clubbing, splenomegaly, and microscopic hematuria also has been proposed. In a study of 100 consecu- tive cases of pathologically proven native valve IE (NVE), inclusion of these additional parameters with the existing Duke minor criteria resulted in a 10% increase in the fre- quency of cases being deemed clinically definite, with no loss of specificity. 