AIDS RESEARCH AND HUMAN RETROVIRUSES Volume 19, Number 12, 2003, pp. 1065–1070 © Mary Ann Liebert, Inc. Two Percent of HIV-Positive U.S. Blood Donors Are Infected with Non-subtype B Strains ERIC L. DELWART, 1,2 SHARYN ORTON, 3 BHARAT PAREKH, 4 TRUDY DOBBS, 4 KENNETH CLARK, 5 and MICHAEL P. BUSCH 1,6 ABSTRACT To estimate the prevalence of HIV strains other than the predominant HIV-1B subtype in the U.S. blood donor population we genetically and serologically characterized HIV in infected blood donations collected throughout he United States from 1997 to mid-2000. Using a combination of DNA heteroduplex mobility and DNA sequence analyses of the env and gag regions of HIV-1 we determined that 285 of 312 infections were caused by HIV-1B and six by non-subtype B HIV-1 (four HIV-1C, one HIV-1AE, one HIV-1A). Genetic dis- tances of greater than 14% in the envelope V3–V5 region of the four HIV-1C strains indicated that they did not share a recent common origin. HIV-1 group M, N, and O, and HIV-2 specific peptide serological testing of the 20 PCR-negative samples determined that one infection was caused by HIV-2 and none by HIV-1 group N and O. The major risk factor for infection with a non-HIV-1B strain was sex with an HIV-infected person from Africa although three of seven non-HIV-1B-infected subjects did not fit that category. For four of seven non-HIV-1B-infected subjects the subtype detected was consistent with the African country of origin of the infected person or of their sexual partner. The frequency of genetically confirmed non-subtype-B HIV infec- tion in a geographicallydispersed group of infected U.S. blood donors in 1977–2000 was therefore 2.0% (6/312). 1065 INTRODUCTION T HE GENETIC DIVERSITY OF HIV within the United States is of interest for tracking the spread of imported variant strains, ensuring the sensitivity of serological screening and viral RNA quantitation methods, and may possibly influence the efficacy of HIV-1B-based vaccine immunogen. 1–7 Unlike Europe, where multiple subtypes of HIV-1 cocirculate, 8–10 a single subtype (subtype B) of the main (M) group of HIV-1 (HIV-1B) still pre- dominates in the United States. 11 An early and rapid spread of HIV-1B, possibly from a point source introduction in the mid- to late 1970s, 12 may account for the predominance of a single HIV-1 subtype in the United States. Nevertheless recent analy- ses have detected nonsubtypeB HIV-1 in the United States. Sub- types A, C, D, E, F, G, A/J, as well as HIV-1 group O infec- tions have been reported in non-national U.S. residents and in U.S. citizens likely to have been infected abroad. 13–18 Trans- missions of non-HIV-1B that appeared to have occurred in the United States include 3A, 1F, 1E, 1B/F, 1A/B, and 1 A/B/E re- combinant subtype viruses. 18–22 As part of a continuing effort to monitor the genetic diversity of HIV in the United States we attempted to genetically subtype 316 HIV strains from blood donors identified in U.S. blood collection sites as anti-HIV-1 and/or HIV-2 seropositive on the basis of routine laboratory screening of whole-blood donations given between 1997 and 2000, and subsequentlyenrolled in the CDC HIV Donor Study. 23 MATERIALS AND METHODS Subjects A total of 7.2 million blood donations were collected in 1997–2000 from the 18 participating blood centers located 1 Blood Systems Research Institute, San Francisco, California 94118. 2 Department of Medicine, University of California, San Francisco, California. 3 Transmissible Diseases Department, American Red Cross Holland Laboratory, Rockville, Maryland. 4 HIV Immunology Branch, Centers for Disease Control and Prevention, Atlanta, Georgia. 5 Division of HIV/AIDS Prevention, Centers for Disease Control and Prevention, Atlanta, Georgia. 6 Department of Laboratory Medicine, University of California, San Francisco, California.