E test as susceptibility test for evaluation of Neisseria meningitidis isolates.

Frank J. Michalski, Ph.D. Diagnostic Virology Laboratory MetPath One Malcolm Avenue Teterboro, New Jersey 07608 Author's Reply We appreciate Dr. Michalski's comments on our study describing the use of quantitative EIA reactivity in predicting HIV seropositivity by Western blot. We agree that the relationship between HIV antibody titer and absorbance is not directly linear, as demonstrated by George (1). Furthermore, one cannot define a true quantitative relationship between a screening test which generates continuous numerical data (HIV EIA) and a confirmatory test with a categorical interpretation (HIV Western blot). However, there is a generally direct relationship between EIA absorbance and HIV antibody titer as measured by serial dilutions (1), and we have demonstrated that one can make semiquantitative use of these quantitative data to predict HIV Western blot positivity with a high degree of reliability. Given the significant clinical and psychological impact of a positive diagnosis of HIV-1 infection, we do not suggest that our algorithm is currently appropriate for widespread use. We do feel that it is an approach which warrants further evaluation and which may find utility at present in situations such as the selected circumstances we suggested (e.g., epidemiologic surveys, rapid diagnosis, and resource-poor settings).