| http://www.w3.org/ns/prov#value | - at 15 clinical sites in the U.S. to investigate the natural history of HIV-1.13 The study design and methods for quarterly follow-up, HIV-1 testing, and viral-load measurement, and immunophenotyping of CD4+ counts, along with demographics, risk behavior, and other clinical data, have been previously described in detail.13,14 Serum samples taken at baseline and at the end of follow-up were tested
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