Heightened Nontesting Risk Mitigation Blood Donor Screening with Retrospective Transcription-Mediated Amplification Testing during a 2023 Autochthonous Florida Malaria Cluster

Transfusion-transmitted malaria risk in the United States is estimated at less than 1 per 10 million blood donations or about one case every 2 years. Since 2000, the 13 transfusion-transmitted malaria case donations were from former residents of a malaria-endemic area who were mostly outside the deferral windows. Recent autochthonous malaria outbreaks occurred in 2002, 2003, and 2023. From May to early July 2023 in Sarasota County, Florida, symptomatic Plasmodium vivax malaria was detected in seven individuals without recent malaria travel history. The local state department of health instituted mosquito control measures and increases in patient malaria syndromic surveillance on May 24th. The local blood center similarly responded to this autochthonous 2023 P. vivax outbreak by implementing a nontesting donor risk mitigation strategy of escalating blood donor screening measures and pathogen reduction to minimize the risk of transfusion-transmitted malaria in presymptomatic donors. In the absence of an approved blood donor screening test for malaria at the time, additional nucleic acid testing on 258 donor samples from four Sarasota zip codes and 178 donor samples from eight Miami zip codes collected from July to October was studied retrospectively using a transcription-mediated amplification with a limit of detection ranging from two to seven infected erythrocytes per milliliter. All donor samples were nucleic acid test nonreactive. No local transfusion transmission malaria cases were reported. Both the Florida Department of Health and the blood center took mitigation steps to decrease mosquito and blood donor transmission risks combined with increased surveillance.