ORIGINAL ARTICLE Dengue viremia in blood donors identified by RNA and detection of dengue transfusion transmission during the 2007 dengue outbreak in Puerto Rico Susan L. Stramer, Jeffrey M. Linnen, James M. Carrick, Gregory A. Foster, David E. Krysztof, Shimian Zou, Roger Y. Dodd, Lourdes M. Tirado-Marrero, Elizabeth Hunsperger, Gilberto A. Santiago, Jorge L. Muñoz-Jordan, and Kay M. Tomashek BACKGROUND: In 2007, a total of 10,508 suspected dengue cases were reported in Puerto Rico. Blood donations were tested for dengue virus (DENV) RNA and recipients of RNA-positive donations traced to assess transfusion transmission. STUDY DESIGN AND METHODS: Blood donation samples from 2007 were maintained in a repository and tested individually for DENV RNA by transcription- mediated amplification (TMA); a subset was further tested by an enhanced TMA (eTMA) assay. TMA- reactive samples were considered confirmed if TMA (including eTMA) was repeat reactive (RR). All TMA-RR samples were tested by quantitative, DENV type– specific reverse transcriptase–polymerase chain reac- tion (RT-PCR) and for anti-DENV immunoglobulin (Ig)M by enzyme-linked immunosorbent assay. Samples posi- tive by RT-PCR were further tested for infectivity in mosquito cell culture. Patients receiving components from TMA-RR donations were followed. RESULTS: Of 15,350 donation samples tested, 29 were TMA-RR for a prevalence of 1 per 529 (0.19%). DENV Types 1, 2, and 3 with viral titers of 10 5 to 10 9 copies/mL were detected by RT-PCR in 12 samples of which all were infectious in mosquito culture. Six TMA-RR samples were IgM positive. Three of the 29 recipients receiving TMA-RR donations were tested. One recipient in Puerto Rico transfused with red blood cells containing 10 8 copies/mL DENV-2 became febrile 3 days posttransfusion and developed dengue hemor- rhagic fever. The recipient was DENV-2 RNA positive by RT-PCR; both the donor and the recipient viruses had identical envelope sequences. CONCLUSIONS: High rates of viremia were detected in blood donors in Puerto Rico coupled with the first docu- mented transfusion transmission of severe dengue disease, suggesting that further research on interven- tions is needed. D engue is a disease caused by four related RNA viruses of the genus Flavivirus, dengue virus (DENV)-1, -2, -3, and -4. 1 However, not all DENV infections result in clinically apparent disease. Approximately 75% of all DENV infections are asymptomatic, including those among adults. 2-6 Each DENV type is capable of causing the full spectrum of disease from nonspecific, acute febrile illness to severe disease including dengue hemorrhagic fever (DHF) and dengue shock syndrome. Approximately 5% of patients with dengue develop severe disease, which is thought to occur more commonly among those with second or subsequent infections. 7 Infection with one DENV-type produces lifelong immunity against that DENV-type and short-term (2 months) cross-protection against ABBREVIATIONS: ARC = American Red Cross; DENV(s) = dengue virus(-es); DHF = dengue hemorrhagic fever; ED = emergency department; eTMA = enhanced transcription- mediated amplification; IR = initially reactive; MAC- ELISA = immunoglobulin M–capture enzyme-linked immunosorbent assay; PDSS = passive dengue surveillance system; RR = repeat reactive; S/CO = signal to cutoff; TMA = transcription-mediated amplification. From the Scientific Support Office, American Red Cross, Gaith- ersburg, Maryland; Gen-Probe, Inc., San Diego, California; Holland Laboratory, American Red Cross, Rockville, Maryland; and VA Caribbean Healthcare System and the Centers for Disease Control (CDC), San Juan, Puerto Rico. Address reprint requests to: Susan L. Stramer, PhD, Scien- tific Support Office, American Red Cross Biomedical Services, 9315 Gaither Road, Gaithersburg, MD 20877; e-mail: stramers@ usa.redcross.org. Received for publication November 7, 2011; revision received December 12, 2011, and accepted December 17, 2011. doi: 10.1111/j.1537-2995.2012.03566.x TRANSFUSION **;**:**-**. Volume **, ** ** TRANSFUSION 1