Injecting drug users need vaccination against hepatitis B

EDITOR—Best et al give us useful information about drug users' perceptions of their hepatitis B and C status and, on the basis of this, recommend that clinicians should test all drug users for hepatitis B and C infection.1 With respect to hepatitis B, however, they fail to mention a more important intervention—namely, immunisation against hepatitis B.

This oversight may partly stem from their failure to distinguish current from past infection. We assume (although they do not state) that by “positive for hepatitis B virus” they mean that the serum was positive for antibody to hepatitis B core antigen. Alone, this marker signifies infection at some time in the past and probable protection against subsequent infection. The marker of active infection (and therefore infectiousness) is hepatitis B surface antigen. Among those infected by drug use one would expect less than a tenth of those with antibody to hepatitis B core antigen to also be positive for hepatitis B surface antigen.2

Drug users who are positive for antibody to hepatitis B core antigen but negative for hepatitis B surface antigen might correctly be informed that they are not at risk of the sequelae of chronic hepatitis B. They might also be told that they are no longer at risk of hepatitis B and that vaccination is unnecessary. Commercial assays for antibody to hepatitis B core antigen may, however, result in false positive test results,3 and patients at risk may therefore be denied the protection of a safe and effective vaccine. A positive result of a test for antibody to surface antigen is a more reliable marker of immunity.

Before recommending widespread testing of drug users we need to know whether knowledge of hepatitis status changes behaviour. In the study of Best et al a high proportion …