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The first case of HCV infection detected before seroconversion in blood donors tested by HCV core antigen ELISA

The existence of a serologic window period is the main reason for the residual risk of HCV transmission through anti-HCV-screened blood. Early during this period, HCV RNA and a core protein (antigen) can be detected in serum.1 Testing blood donors for one of these viral constituents could further reduce the already low risk of transfusion-transmitted HCV infection. In fact, from the late 1990s, an increasing number of blood banks in Europe and the US have included mini-pool NAT for HCV RNA in their donor screening protocols. Recently, an HCV core antigen ELISA (Ortho-Clinical Diagnostics, Raritan, NJ) has been shown to be highly sensitive and specific for detecting HCV infection during the antibody-negative window period.2 The HCV core antigen ELISA can be performed on individual donor samples by use of the laboratory procedures and equipment that are familiar to blood banks. We have included the first-generation HCV core antigen ELISA in the routine screening of blood donors since September 2000. The ELISA is performed according to the manufacturer’s instructions. Initially reactive samples are tested again in duplicate, and those that are repeatedly reactive are checked with a confirmatory test based on neutralization with high-titer, human, polyclonal anti-HCV core antigen (Ortho-Clinical Diagnostics). Among the 29,468 donor samples that were tested between September 2000 and September 2001, 204 (0.69 percent) were initially reactive, 106 (0.36 percent) were repeatedly reactive, and one was confirmed by the neutralization test. To the best of our knowledge, this is the first reported case of antibodynegative HCV infection detected among blood donors by use of the HCV core antigen ELISA. The donor was a 28-year-old man who was donating for the first time. At the predonation interview, he denied any medical history or risk behavior that could have deferred him from donation. However, when he was asked again after the screening test results were known, he admitted a casual, “nonprotected” sexual relationship 30 days before the blood donation with a female partner whom he later suspected could be engaged in high-risk behaviors. Table 1 shows results of the laboratory tests performed on the initial sample and the one taken 30 days later. For both samples, anti-HIV-1 and -2, HBsAg, and a serologic test for syphilis gave negative results. Although sexual transmission is not considered an effective route for HCV transmission, approximately 15 to 20 percent of patients with acute HCV infection have a history of sexual exposure in the absence of other risk factors.3 Efficacy of sexual transmission seems to increase with high-risk sexual practices, which have been present in other reported cases of HCV infection detected by NAT before seroconversion.4,5 There are few data on the performance of the HCV core antigen ELISA in the routine testing of blood donors. No more than 22,000 test results have been reported in three different studies. Rates of initially and repeatedly reactive test results in these ranged from 0.58 to 0.65 percent and 0.08 to 0.26 percent, respectively.6-8 Although in our hands the positive predictive value of the HCV core antigen ELISA for a positive neutralization test was low (1 in 106), the positive predictive value of the combination of both tests for positive NAT may be high, because the only sample with a positive neutralization test result contained HCV RNA. The high viral load found in this preseroconversion sample would have been detected by mini-pool NAT. By using seroconversion panels, Lee et al.6 reported a sensitivity of 94 percent for the HCV core antigen ELISA, as compared with sensitivity in individual-sample NAT. Until now, no comparison of the results of the HCV antigen ELISA and mini-pool NAT (as it is usually performed in blood centers) has been reported. However, a recent study on pooled-sample HCV NAT conducted in a donor population very similar to ours found only two