HIV is a pathogen that causes acquired immune deficiency syndrome and was first identified in 1983 [1]. The risk of transmission through transfusion was suggested in a case of Pneumocystis jirovecii pneumonia in a patient with hemophilia A treated with a factor VIII concentrate [2]. Furthermore, in the 1980s, reports indicated that over 50% of patients with hemophilia A had HIV antibodies [3]. As these risks became known, the need for HIV screening tests before blood donation became apparent. In the USA, the HIV antibody test was introduced in 1985 as a screening test for blood donations [4]. Since the development of the nucleic acid test (NAT), which shortens the window period to approximately 10 days, many countries have adopted NAT as an HIV screening test. However, some countries still exclusively perform HIV antibody tests based on the assumption that there are minimal additional cases that can be detected with NAT but not antibody testing. Furthermore, given the trend to regard HIV as a controllable disease, there is assumed to be no need to conduct an expensive test universally. In Korea, NAT for HIV detection was introduced in 2005 as a screening test for blood donations [5].

HBV was first discovered by Blumberg in 1964 [6]. Before the 1970s, approximately 6% of patients who received multiple transfusions had transfusion-transmitted HBV [7]. HBV tests can be broadly divided into serological and DNA tests. Serological tests detect HBsAg, anti-HBs antibody, and anti-HBc antibody. The United States Food and Drug Administration (FDA) mandates testing for HBsAg, total anti-HBc antibodies, and HBV DNA in blood donations. In Korea, only HBsAg and HBV DNA tests are regularly performed. Korea is classified as an HBV intermediate endemic area, with a higher prevalence of HBV infection than Western countries. Therefore, HBV testing was one of the first screening tests introduced in Korea in the 1970s. Although the national vaccination program has led to a gradual decrease in HBV prevalence, the estimated residual risk remains higher than that in Western countries [5, 8].

Before the identification of HCV, post-transfusion hepatitis non-A, non-B (PTH-NANB) was reported in over 10% of patients who had received blood transfusions. However, with the identification of HCV in 1989 and the introduction of the HCV antibody test, transfusiontransmitted HCV incidence sharply decreased [9, 10]. The HCV antibody test was introduced as a blood-donation screening test in the USA in 1990 and in Korea in 1991. Subsequently, in 2005, the HCV NAT was introduced to further reduce the risk, and is now rapidly spreading to many other countries [11]. In Korea, the residual risk of transfusion-transmitted HCV infection is approximately 0.27 per 106 transfusions [5]. A distinctive aspect of blood donor screening in Korea is the alanine transaminase (ALT) test, which is not performed in Western countries [12]. ALT tests have long been used to detect PTH-NANB. However, with the discovery of HCV infection and the development of new test methods, ALT tests are no longer routinely performed in most countries. In the USA for example, ALT testing was excluded from blood donor screening in the 2000s. In Korea, despite changing the criteria for inappropriate blood from 65 to 101 IU/mL, the ALT test is still included in blood donation screening. Nevertheless, to prevent unnecessary disposal of limited blood resources, indepth discussions are needed to determine whether ALT testing is still required.

WNV is an ssRNA virus in the Flaviviridae family that causes a vector-borne disease. Due to its geographical distribution, WNV has received relatively less attention in Asia. However, in North America and Europe, it is a clinically important infectious agent, and TTI cases have long been reported [13]. NAT is more effective for preventing WNV TTI than serological tests. Therefore, in many Western countries, WNV NAT has been widely used for screening blood donations, leading to the development and utilization of numerous commercial platforms [4, 14].

The Zika virus, another vector-borne pathogen, typically causes asymptomatic infection in humans; however, it can occasionally lead to severe disease, resulting in fatal outcomes for fetuses. Although Zika virus is typically transmitted by mosquitoes, TTIs have also been reported. In a study in Brazil, 0.16% of blood donors tested positive for Zika virus RNA [15]. Methods such as NAT and pathogen inactivation (PI) are effective for preventing Zika virus TTI [16]. In Korea, there is currently no regular screening for WNV or Zika virus.

HTLV is a lipid-enveloped RNA retrovirus that causes adult T-cell leukemia/lymphoma in humans. Infection routes include vertical transmission, sexual contact, and transfusion. Transfusion-related transmission is usually associated with blood cell components. In Korea, blood donation screening has included anti-HTLV antibody testing since 2008, covering all donated blood samples. The prevalence of anti-HTLV antibody positivity among donated blood samples in Korea is 0.027% [17]. As HTLV is found within white blood cells, implementing leukoreduction can reduce transmission risk [4].