An independent quality assurance program has been established by the Division of AIDS, National Institute of Allergy and Infectious Diseases, for monitoring virologic assays performed by nearly 40 laboratories participating in multicenter clinical trials in the United States. Since virologic endpoints are important in evaluating the timing and efficacy of therapeutic interventions, it is imperative that virologic measurements be accurate and uniform. When the quality assurance program was initially created, fewer than 40%o of the laboratories could consistently recover human immunodeficiency virus (HIV) from peripheral blood mononuclear cells (PBMCs) of HIVinfected patients. By comparing coculture procedures in the more competent laboratories with those in laboratories who were struggling to isolate virus, optimal conditions were established and nonessential reagents and practices were eliminated. Changes were rapidly introduced into a laboratory when experience dictated that * Corresponding author.
This study reports the rates of phenotypic switching in strains of Candida albicans isolated from superficial and invasive infections. Of 19 invasive strains, 68% showed switching activity, often at very high rates, compared with only 28% of 40 strains isolated from superficial sites (P = 0.004).
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