The findings of a long-term study of injection drug users newly infected with Hepatitis C virus (HCV) show that antibodies to the virus may not appear in the blood until two months after they have been infected.

These results “underscore the importance” of nucleic acid screening of blood donations to prevent HCV transmission, researchers say. The findings also reaffirm the need to follow HCV-positive injection drug users long-term to check for viral persistence.

Among 179 HCV antibody-negative injection drug users followed in the study, an “alarming” 34 percent became infected despite risk reduction counseling, Dr. Andrea L. Cox, from the Johns Hopkins Medical Institutions in Baltimore, Maryland, and colleagues report in the medical journal Clinical Infectious Diseases.

As expected, individuals with early-phase HCV infection were largely without symptoms. Virus in the bloodstream was the earliest sign of HCV infection, preceding the detection of HCV antibodies by 5 to 6 weeks, and in one case, by more than 12 months, the investigators report. However, in all other cases, HCV RNA was detected no more than 63 days before antibodies appeared.

Liver enzyme function measurements were also elevated during early-phase HCV infection, but did not correlate closely with HCV RNA levels or viral persistence. None of the infected patients developed jaundice.

In cases of viral persistence, stable blood levels of HCV RNA were noted in some individuals within 2 months after the virus was first detected in the blood, while in others, it was not apparent until more than 1 year later.

In individuals who cleared the virus from their system, HCV became persistently undetectable as early as 94 days and as late as 620 days after initial infection.

SOURCE: Clinical Infectious Diseases, April 1, 2005.