High Incidence of Chikungunya Virus and Frequency of Viremic Blood Donations during Epidemic, Puerto Rico, USA, 2014.

Chikungunya virus (CHIKV), a mosquitoborne, positive-sense RNA virus of the family Togaviridae, causes an acute febrile illness and severe polyarthralgia that can persist for months or years in some patients (1–3). Serious outcomes and deaths are rarely observed. However, newborns and other vulnerable populations are at risk for severe complications (4). In late 2013, cases of CHIKV infection were reported in the French Collectivity of Saint Martin, which is part of the French Antilles (5), constituting the first instance of autochthonous transmissions of CHIKV in the Americas in the past century (6). In an immunologically naive population, CHIKV spread rapidly throughout the Caribbean region and beyond to most countries in the Western Hemisphere (7), including 11 autochthonous cases reported in Florida, USA, in September 2014 (8). CHIKV has yet to be demonstrated to be transmissible by blood transfusion (9). However, this finding might result from difficulties in discriminating transfusion transmission from locally acquired mosquitoborne infection. Transfusion transmission is probable, given previous instances of laboratory-acquired infections and infection of healthcare workers by blood exposures (10). Asymptomatically infected persons can have viral loads >105 PFU/mL (11,12) and are a substantial risk for transfusion transmission. Estimates of asymptomatic CHIKV infection vary widely. A recent study in Puerto Rico (13) confirmed previous estimates that 10%–25% of total infections are subclinical (14–16). However, other studies with the Asian genotype suggest that a greater proportion of cases might be asymptomatic or have only mild and transient symptoms (17,18). CHIKV infection can result in viral loads >108 PFU/mL (19). Thus, relatively high viral loads likely present in some presymptomatic donors might be a threat for transfusion transmission. Recently, a case of transfusion transmission of the related alphavirus Ross River virus, has been reported (20), stemming from transfusion of the erythrocyte component from a blood donor who reported symptoms of Ross River virus infection 2 days after donating blood. To mitigate the theoretical risk for transmission, some blood collection organizations in regions with large CHIKV epidemics have suspended local blood collection, implemented nucleic acid amplification testing (NAAT) of erythrocyte and plasma donations for CHIKV RNA, and introduced pathogen-reduction technology for platelet components (21,22). To directly assess the threat that CHIKV poses to the blood supply, and given the absence of licensed NAAT for donor screening, we conducted NAAT surveys of blood donors in Puerto Rico during the 2014 epidemic and complementary serosurveys before and after the epidemic.