Antenatal screening for syphilis

Congenital syphilis in children is rare in Britain, and most doctors will never have seen a case. The only routine data currently available are reports from genitourinary medicine clinics, the KC60 returns. In the last two years for which data are available (1991 and 1992) clinics in England reported 220 new diagnoses of infections syphilis in women (pregnant or otherwise) and five of congential syphilis in children under 2.^1,2 Women identified through antenatal screening, however, may not be treated in genitourinary medicine clinics, and some infected children may be seen only by paediatricians - so that the true incidence of both conditions is unknown.

What can be done to prevent congenital syphilis? Transmission from mother to child usually takes place after four months' gestation, so early antenatal serological screening and treatment prevent most cases. Detection later in pregnancy is less effective, but even postnatal treatment of an infected child prevents many sequelae. Tests occasionally miss maternal infection, especially if only reagin agglutination tests (rapid plasma reagin or Veneral Disease Reference Laboratory test) are used,3 and though new maternal infections may occur in late pregnancy, this will happen rarely in a country where the incidence of the disease is low. If there is any reasonable possibility of active syphilis in pregnancy it is best to treat it with injectable penicillin.4 Apart from causing very rare Jarisch-Herxheimer reactions, this treatment is safe and highly effective. Unfortunately, maternal treatment with erythromycin in cases of penicillin allergy does not reliably treat fetal infection.4 A child born to a mother who may have been infected requires careful examination and follow up with serological monitoring. Again, treatment should be given if there is a suspicion of active infection or if maternal treatment has been suboptimal.4

General practitioners, paediatricians, and obstetricians need to be aware that congenital syphilis still occurs.5 It should be suspected after stillbirth and in infants with persistent jaundice, non-specific fever, anaemia, or failure to thrive (classic features such as “snuffles” or a desquamating rash are rare).6 Once the diagnosis is suspected specialist advice should be taken. Specialists in genitourinary medicine are best able to diagnose the disease in mothers (who will be at risk of other sexually transmitted diseases) and they will notify partners. Interpreting the result of tests for syphilis, in adults and children, may not be easy without advice from specialists, particularly if there is concurrent HIV infection.7 In England and Wales the network of public health laboratory service reference laboratories is available to help in the selection of tests and interpretation of their results.

Some authorities now question the need to continue screening pregnant women given the apparent low level of infection.8 Although in Britain the incidence of infectious syphilis in women may be low, it may not remain so indefinitely. Indigenous cases of syphilis have increased recently in the United States, where failure to deliver universal early antenatal care (including screening) has permitted an epidemic of acquired syphilis in adults to be translated into an epidemic of congenital syphilis9 with rates among infants increasing from 4.3/100 000 live births in 1982 to 94.7/100 000 in 1992.10 Factors driving the American increase - poverty and use of drugs^6,9 - are prevalent in Britain. A more important reason for new acquired and congenital infection in Britain may be international spread. All sexually transmitted disease, including syphilis, are commoner in developing countries11 and are often spread through travel and migration.12 Between 1989 and 1991 two thirds of the cases of early infectious syphilis seen in a south London genitourinary medicine clinic were imported.13

Several new surveillance initiatives will enhance our knowledge of the incidence of syphilis in Britain. Last year, the Public Health Laboratory Service and St Mary's Hospital, London, began a survey of congenital syphilis through the British Paediatric Surveillance Unit. Complementing this will be survey of syphilis in pregnancy and congenital syphilis conducted by the British Cooperative Clinical Group of consultants in genitourinary medicine. In both these surveys doctors are asked to report the number of new cases that they have seen over a period even if the total is zero.

A preventive strategy for congenital syphilis will include general measures to prevent sexually transmitted disease. But if congenital syphilis is to remain rare not only clinicians but also managers of provider units, purchasers, and public health physicians must be aware that it still occurs. Should antenatal screening remain integral to the preventive strategy? Past assessments have concluded that considerable benefit resulted from screening pregnant women in Britain,^14,15 although these analyses used historical data and a reappraisal is needed. This reappraisal will require the results of the enhanced surveillance, which because the condition has a low incidence, will take some time to accure. Meanwhile, it is important to continue universal antenatal screening for syphilis.