Reply to King and Stover.

TO THE EDITOR—We appreciate the response of King and Stover [1] to our recent article [2]. The authors bring up the important issue of piperacillin-tazobactam and its association with positive serum galactomannan index assays due to the presence of antigenic epitopes in many branded preparations. In our report, we did not comment on the use of branded or generic piperacillin-tazobactam in our patient cohort. At our institution, ceftazidime is administered as the first-line empiric treatment for fever and neutropenia in allogeneic hematopoietic stem cell transplant (HSCT) recipients. In contrast, branded or generic piperacillin-tazobactam formulations are not routinely used for prophylaxis or treatment purposes in allogeneic HSCT patients at our institution. In our cohort, only 2 patients (of 210) received piperacillin-tazobactam within 7 days leading up to serum and bronchoalveolar lavage galactomannan index testing. One of the patients had a negative serum galactomannan index, and the other had a positive serum galactomannan index (0.685, confirmed); the latter patient had both a chest computed tomography scan and a clinical course compatible with invasive aspergillosis. Due to the small number of patients (1%) receiving this drug in our study, piperacillintazobactam administration was not included in our multivariate analysis and does not impact our study conclusions. We agree with King and Stover that it is important to be cognizant of piperacillintazobactam use and of its potential to cause false-positive test results. Although piperacillin-tazobactam was not a factor in our study due to lack of usage of this antibiotic, we appreciate the opportunity to clarify this important issue.