Increasing syphilis cases in Japan: A risk posed to blood services

Syphilis cases surged in Japan, exceeding 10,000 in 2022, primarily through heterosexual transmission. The Japanese Red Cross Blood Services (JRCBS) screens donated blood for syphilis, disqualifying positive donors. This study explores syphilis infection among blood donors to understand its impact on blood collection and supply.

Data from blood donors (2015-2022) at JRCBS were analysed. Treponema pallidum (TP) antibody was tested by chemiluminescent enzyme immunoassay or chemiluminescent immunoassay. A total of 39,199,047 donations were scrutinized. Reactive samples were further tested by rapid plasma reagin (RPR).

The number of TP and RPR positives (referred as syphilis positives) in 2022 compared with 2015 increased by 1.7 times in blood donors and 4.9 times in the general population. High syphilis-positive rate in 2022 was mainly observed among male first-time/reactivated donors and females in their 20s and 30s. Although syphilis cases in general population declined during the Corona pandemic, no significant decrease occurred in syphilis-positive donors.

Although the increase in syphilis positives among blood donors may be a reflection of the increase in the general population, the rate of increase was less pronounced among blood donors. Although the increase in the syphilis-positive rate may not affect blood product safety, it would have a significant impact on the number of potential blood donors in the future because the increase was more frequently observed in young donors and new donors, and currently, syphilis-positive individuals are permanently deferred from blood donation. The implementation of effective measures to prevent transmission in the general population is required.