A promising diagnostic tool for toxoplasmic encephalitis: tachyzoite/bradyzoite stage-specific RT-PCR

Objectives: To determine the diagnostic accuracy, technical benefit, and clinical application of the duplex reverse transcription-PCR (duplex RT-PCR) assay specific to bradyzoite (BAG1) and tachyzoite (SAG1) genes, for diagnosing toxoplasmic encephalitis (TE) in HIV-infected patients, using the US Centers for Disease Control and Prevention (CDC) recommended diagnostic criteria as the reference standard. Methods: Advanced HIV-infected individuals with central nervous system opportunistic infections were enrolled in a prospective study, performed from July 2007 to January 2009; patients were classified as TE- or non-TE subjects in accordance with the CDC recommended criteria. Blood and cerebrospinal fluid samples were assayed by duplex RT-PCR to detect tachyzoite, bradyzoite, both, or none. Results: A total of 61 advanced AIDS patients were included in the study, eight with TE and 53 as non-TE subjects. The duplex RT-PCR assay showed high diagnostic accuracy, with 100% specificity and positive predictive value, as well as 87.5% sensitivity. Its efficacy reached 98.3%. This diagnostic method was rapid, needed only moderately skilled technicians, and was four times cheaper than procedures used in the CDC diagnostic recommendations. It worked very well for blood samples, even after drug treatment had been started. Conclusions: The duplex RT-PCR assay is simple and rapid, and provides high efficacy with lower costs than the reference standard procedures. This is a promising alternative diagnostic tool for TE in HIV/AIDS individuals, especially in resource-limited settings. (C) 2012 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.