Letters

Accuracy of perceptions of hepatitis B and C status

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 of drug users had previously been tested for hepatitis B and C. Despite this the high prevalence of both infections and the incorrect self reporting of status suggest that testing may have little effect on behaviour. Meanwhile, the number of cases of acute hepatitis B among drug users is increasing,⁴ and, despite the availability of a highly effective vaccine, too few have been offered that intervention. We recommend that hepatitis B vaccine be offered to drug users at every opportunity and not be delayed while results of antibody testing are awaited.

M E Ramsay , consultant epidemiologist. 
mramsay@phls.nhs.uk

M A Balogun , clinical scientist. 
Immunisation Division, PHLS Communicable Disease Surveillance Centre, London NW9 5EQ

C G Teo , consultant virologist. 
P P Mortimer , director. 
Hepatitis and Retrovirus Laboratory, PHLS Central Public Health Laboratory, London NW9 5HT

1.	Best D, Noble A, Finch E, Gossop M, Sidwell C, Strang J. Accuracy of perceptions of hepatitis B and C status: cross sectional investigation of opiate addicts in treatment. BMJ 1999; 319: 290-291 [Full Text] . (31 July.)
2.	Hyams KC. Risks of chronicity following acute hepatitis B virus infection: a review. Clin Infect Dis 1995; 20: 992-1000 [Medline] .
3.	Weber B, Michl U, Muhlbacher A, Paggi G, Bossi V. Evaluation of the new automated Enqymun-Test Anti-HBcPlus for the detection of hepatitis B virus core antibody. Intervirology 1998; 41: 17-23 [Medline] .
4.	Acute hepatitis B in injecting drug users is increasing as initiative to improve vaccination coverage begins. Commun Dis Rep CDR Wkly 1999; 9: 183 , 186.

Authors' reply

EDITOR - We agree with Ramsay et al about the importance of hepatitis B immunisation.¹ The short report that these letters are commenting on, however, concerned the accuracy of perceptions; hence the issue of immunisation was not discussed, particularly in view of the limitations on word count. The point may be pertinent but does not alter our conclusions.

Judd et al ask about the blood tests that were used. They measured antibodies to hepatitis C and viruses; we did not measure antigens.

The aim of the study was to examine the relation between the drug users' perception of their status and their actual status; we are aware that many of the users' responses would have been guesses. This is not, however, a limitation of the study - indeed it is precisely this point that makes the findings so important. It is the participants' beliefs about their status that will influence their risk taking, not their actual status. Actual status determines risk, but it is belief about status that influences behaviour.

With regard to the final sentence of Judd et al, the reference to "evidence" is, in fact, no more than a reference to their own previous assertions on the topic; it is hence still compatible with the observation of Ramsay et al of the lack of evidence.

The crucial point from our study is that many of our subjects had inaccurate beliefs about their status, particularly those who believed that they were negative when they were, in fact, positive. If Ramsay et al are accurate in their conclusion that knowledge of hepatitis status has little impact on behaviour then this may be of little benefit in terms of prevention. In contrast, if knowledge is associated with behaviour change (as changes in needle sharing after the HIV epidemic suggest) then increasing drug users' knowledge of their hepatitis status has important implications for the prevention effort.

This also challenges the assumption of Suckling et al that treatment for seropositive status can only ever be in the form of a medicine. Education campaigns with injecting drug users after the initial spread of HIV shows that behaviour change is a realistic goal, but it is predicated on education and knowledge. Behaviour change is precisely the "treatment response" that needs to be achieved with educational work and a range of therapeutic approaches with seropositive patients to benefit them, their intimates, and the wider populations. Thus services can promote behaviour changes within the harm reduction paradigm,² regardless of pharmacotherapies for hepatitis C.

Finally, the fear that services might be overburdened if patients positive for hepatitis C virus were encouraged to seek an established effective treatment is discriminatory on the grounds of diagnosis. The NHS cannot withhold an effective new treatment simply because its provision would be a burden or because the patient population is unpopular and lacks effective advocacy.

David Best , research coordinator. 
d.best@iop.kcl.ac.uk

Alison Noble , clinical researcher. 
Emily Finch , consultant psychiatrist. 
Michael Gossop , head of research. 
Clare Sidwell , clinical researcher. 
John Strang , director. 
Institute of Psychiatry, National Addiction Centre, London SE5 8AF