Antenatal screening for carriers of hepatitis B virus

Britain needs a standardised nationwide universal screening programme

Acute hepatitis B is becoming much less common in Britain now that blood and blood products are safe, health care staff are being vaccinated, infectious health care workers are being steered away from procedures that could transmit the virus, drug misusers have needle exchange schemes, and sexually active people have counselling and condoms. The current morbidity and mortality from hepatitis B mostly result from the chronic carrier state,1 and the prevention of persistent infection must be central to any strategy to control the virus and its effects.

The probability that infection with hepatitis B will become persistent decreases with the age at which infection occurs. Between 60% and 90% of babies born to the most infectious mothers (those positive for hepatitis B e antigen) become carriers if infected perinatally, whereas this happens to less than 10% of those people infected as adults.1 2 3 Perinatal infection can be prevented by prompt administration of immune prophylaxis at birth,4 5 and the prevention of perinatal infection in this way will have a substantial impact on the numbers of carriers in the future.

The Netherlands is one of Britain's closest neighbours in Europe, and its population includes immigrants from other parts of Europe and from parts of Asia, reflecting its colonial past. The two countries compare much better with each other than with the United States, with its financially polarised health care system. Britain should take advantage of two Dutch reports published in this week's journal (p 1197,6 p 12007). Data have been gathered on antenatal screening for carriage of hepatitis B in nearly 100000 women over seven years in four centres. The results, therefore, present the overall position in the Netherlands with great accuracy.

Any programme to prevent perinatal infection must identify mothers who are carriers of hepatitis B virus. Within a largely European population the prevalence of infection can be expected to be relatively low, so some screening system is needed to identify the pregnancies at risk. Screening in late pregnancy proved not to be practical in those areas where half of the women were delivered at home under the care of midwives. The answer found was to incorporate screening for hepatitis B surface antigen with the antenatal screening tests for blood group and for syphilis routinely carried out at 14 weeks. This approach found 705 women who were positive for the surface antigen, of whom only two proved not to be long term carriers. The effectiveness of the screening programme was checked by looking for the results of screening tests at delivery and by cross checking the laboratory screening lists against birth registrations. Coverage in excess of 95% was reached by all centres by the end of the study. Of the 99706 women screened, 97.3% were screened prenatally; only 2.7% needed screening at delivery. The overall prevalence of carriage of hepatitis B surface antigen was 0.74%, with higher rates in big cities--Rotterdam and Utrecht--and lower rates in rural areas, the suburbs, and communities with high socioeconomic indicators.

Unsurprisingly, the mothers presenting at delivery without antenatal care had a higher risk of being carriers of hepatitis B virus (4.0%) and included more women in their first pregnancy. Sixty five per cent of the carrier women identified were European, and in a small study on women of Dutch origin in one centre a risk factor could be identified in only about half.

Many previous studies in countries with low endemicity, such as Britain and North America, have looked at selective versus universal antenatal screening.8 9 10 11 12 When a direct comparison has been made, selective screening failed to identify about half of the women whose babies were at risk.8 9 10 Among the reasons for the failure of selective systems are the difficulty of discussing risk behaviour in a busy antenatal clinic, the possibility that women with no risk factors might have been infected by a partner with a “risk history,” and many infected women have no recognised risk factors. Selecting all non-European women would discriminate against the indigenous population--whose babies also need to be protected against this infection. As a result of the study in the Netherlands the Dutch national health authority has adopted as policy non-selective screening for hepatitis B infection with tests for blood group and syphilis early in pregnancy. Laboratories were requested to add an assay for hepatitis B surface antigen to their screening package for “a nominal sum.”

In Britain the policy on antenatal screening for hepatitis B surface antigen acknowledges that selective screening fails to identify some carriers and that clinics should therefore consider offering screening to all patients.13 In a recent survey 32 districts out of 198 in England and Wales were found to be operating a universal screening policy, while 126 offered selective screening--not necessarily all on the same basis--but those districts offering universal screening were estimated to account for 27% of all the pregnancies (J Heptonstall, personal communication). Where universal testing was being offered the blood samples obtained at antenatal booking were tested by the regional blood transfusion centres, with confirmatory tests and tests for infectivity being referred to regional virology laboratories.

Previously, new large scale initiatives in public health have rarely happened without new funding, and finance may be one of the obstacles to the adoption of universal antenatal screening for hepatitis B in Britain. The cheaper the screening test the closer the cost of universal screening matches the cost of selective screening when the additional “interview” time is taken into account.14

In those parts of Britain where universal screening has been in place longest regional blood transfusion centres carry it out. The transfusion centres are computerised and automated for screening hundreds of blood samples each day. The huge workload with blood donors assures the lowest possible costs of reagents for antenatal screening, and, so long as the close links with virology reference laboratories ensure that all reactive samples are referred for confirmation those laboratories will continue to test for markers of infectivity and advise the maternity units directly.

We need a standardised, nationwide universal screening programme for hepatitis B carriage. The blood transfusion service is likely to be the most cost effective provider.