• M Mikulska, E Furfaro, V Del Bono, A M Raiola, S Ratto, A Bacigalupo, and C Viscoli.
• Division of Infectious Diseases, San Martino University Hospital and University of Genoa, Genoa, Italy. m.mikulska@unige.it
• J. Antimicrob. Chemother. 2012 Jul 1; 67 (7): 1746-8.

ObjectivesGalactomannan (GM) testing is extremely useful for diagnosing invasive aspergillosis in high-risk patients, but false-positive results have been reported in patients treated with piperacillin/tazobactam. The aims of this study are to test if the recent piperacillin/tazobactam (Tazocin™; Pfizer) preparation still contains GM, and if serum GM positivity in haematopoietic stem cell transplant (HSCT) recipients receiving piperacillin/tazobactam can be attributed to this treatment.Patients And MethodsSerum samples obtained from 1 October 2009 to 31 October 2010 from HSCT recipients for GM testing were analysed. The difference in the rate of positive results (defined as GM ≥ 0.5) in patients receiving and not receiving piperacillin/tazobactam was evaluated. Piperacillin/tazobactam vials from randomly selected batches were tested.ResultsOf 1606 samples drawn in the absence of piperacillin/tazobactam therapy, 25 (1.6%) tested positive for GM versus 10 of 394 samples (2.5%) drawn while on piperacillin/tazobactam (P = 0.18). The median GM result of samples drawn on piperacillin/tazobactam was slightly higher than that of samples drawn in the absence of piperacillin/tazobactam (0.141 versus 0.122; P < 0.001). All 90 piperacillin/tazobactam vials from 30 randomly selected batches tested negative for GM, with a median GM value of 0.057 (range: 0.011-0.320).ConclusionsAlthough some residual GM might still be present in piperacillin/tazobactam, currently available brand piperacillin/tazobactam preparations seem no longer responsible for false-positive GM results.

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