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CHICAGO -- A novel new assay that quantitatively detects reverse transcriptase (RT), an enzyme associated with HIV-1 particles, appears to detect HIV infection in the plasma of newborns during the first two weeks of life - up to two weeks earlier than the tests currently used. Because the medications used to treat HIV infection are potentially toxic and difficult to administer to newborns, having earlier diagnostic and prognostic information could be critically important, according to Emory University researcher Ronald Reisler, M.D., who presented test results on the new assay at the 5th Conference on Retroviruses and Opportunistic Infections in Chicago Feb. 1-5.

The study was led by Walid Heneine, Ph.D., of the Centers for Disease Control and Prevention (CDC) and Donald M. Thea, M.D., an investigator at the Medical and Health Research Association, Inc. of New York, in collaboration with investigators at Emory University. The scientists studied stored samples from 56 HIV-infected newborns enrolled at birth in the NYC Perinatal HIV Transmission Collaborative Study conducted at seven New York City health care centers between 1990 and 1994. Serum from the newborns was tested using an HIV DNA polymerase chain reaction (PCR) assay, an HIV RNA viral load PCR assay using the nucleic acid sequence-based assay (NASBA), and for reverse transcriptase activity using the new assay, called Amp-RT.

Through the first 12 days of life the proportion of children with detectable reverse transcriptase activity (RTa) using the Amp-RT assay was higher than that of children with either detectable RNA-PCR through the NASBA assay or DNA PCR, although the difference did not reach statistical significance, given the small sample size. By five days of life, 50 percent of children were RTa positive, while only 30 percent had detectable RNA, and only 20 percent had detectable DNA.

"The current HIV diagnostic tests are inadequate in regard to neonatal diagnosis," said Dr. Reisler. "HIV culture is highly sensitive and specific by age three months, DNA-PCR is highly sensitive and specific by age six weeks, and RNA-PCR is highly sensitive and specific by age two weeks. While Amp-RT and NASBA sensitivity were essentially equivalent after 14 days of life, Amp-RT made the diagnosis earlier," he added. "Moreover, while RNA-PCR has been demonstrated to predict disease progression in neonates during the second month of life, Amp-RT seems to predict disease progression during the first month of life."

Not only does Amp-RT appear to be ultrasensitive, it may be more functional than the other tests, Dr. Reisler points out. Although scientists know that the progression of HIV infection and destruction of the immune system may be caused by actively infectious viral particles, other assays currently used to detect HIV viral load, including NASBA and Amplicor, measure total genomic RNA without distinguishing between functional and non-functional RNA. When HIV replicates, the non-infectious viral particles out-number the infectious particles. The Amp-RT assay measures only viruses with functional RT and is one million-fold more sensitive than conventional RT assays, according to Dr. Reisler.


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