Syphilis in pregnant women and their children in the United Kingdom: results from national clinician reporting surveys 1994-7

Introduction

Infectious syphilis in a pregnant woman usually results in miscarriage, stillbirth, or a congenitally infected baby.1 Risk of transmission diminishes as maternal syphilis advances, but in early latent (asymptomatic) syphilis the risk of vertical transmission remains about 30% to 60%.2 Maternal infection is, however, detectable by serological screening and entirely treatable with penicillin, which also prevents vertical transmission.3 Although screening in the United Kingdom is routine,2 there is no stated policy and the numbers of maternal cases detected are unknown.4

The number of cases of adult syphilis and childhood congenital syphilis seen at genitourinary medicine clinics in the United Kingdom diminished after 1980,5 eventually resulting in calls for abandoning antenatal screening.4 The prevalence of infectious syphilis, however, has remained high in developing countries, and congenital syphilis re-emerged dramatically in the United States in the 1980s and more recently in the newly independent states of the former Soviet Union.2 The low numbers of congenital cases in the United Kingdom might be because there is no maternal syphilis or because maternal syphilis is being successfully detected and treated or because early congenital cases are seen outside genitourinary medicine clinics by paediatricians. Which of these possible explanations is correct is vital to determine an evidence based rational and efficient screening policy, particularly when screening itself has economic and social costs.6

Methods

To determine why there are low numbers of cases of congenital syphilis two national surveys (duration 1994-7) were undertaken with active surveillance; firstly, of genitourinary medicine specialists (through the British Cooperative Clinical Group) to whom most pregnant women positive for syphilis are referred for assessment and, if necessary, for treatment; and, secondly, of paediatricians (through the British Paediatric Surveillance Unit of the Royal College of Paediatrics and Child Health). 2 4 These had objectives of determining minimum incidences of pregnant women with syphilis who require treatment in pregnancy and of congenital syphilis in children born in the United Kingdom. Response rates for the surveys were over 70% and 90%, respectively. Each maternal case report was reviewed and classified by two experienced physicians. Congenitally transmissible syphilis was defined as including primary, secondary, and early latent syphilis.2

Results

The genitourinary medicine survey found 139 cases of women treated for syphilis in pregnancy for which data were available, 121 detected through antenatal screening (table). Thirty one (22%) cases were categorised as definite or probable congenitally transmissible syphilis.2 The Thames regions were overrepresented (73%), but women were treated for syphilis in pregnancy in every region, apart from East Anglia. There was also overrepresentation of ethnic minority groups and women born outside the United Kingdom, though 14% of all cases (19 of 139) and six congenitally transmissible cases were in white women born in the United Kingdom. When country of residence was reported 93% (114 of 123) were resident in the United Kingdom. When probable country of infection was reported 18 of 23 congenitally transmissible cases resulted from transmission abroad, all in developing countries and none in the former Soviet Union (table). Five women were reported as not having received any antenatal care before attending for genitourinary assessment. One woman was reported as being a commercial sex worker, and three injected drugs.

Seventeen children born in the United Kingdom were reported as meeting case definitions for congenital syphilis.7 None had definitive syphilis (which requires direct evidence of Treponema pallidum7), nine were presumptive, and eight were possible cases. Eight were from the Thames regions and nine from ethnic minority groups. Seven mothers had not received antenatal care or did so too late to receive treatment. Three children had clinical abnormalities; two had signs on x ray pictures (one osteochondritis of the skull), and the third had hepatosplenomegaly, rhinitis, oedema, and thrombocytopenia. The three mothers had been either untreated or inadequately treated for syphilis during pregnancy.3

Discussion

These data represent a minimum incidence of congenitally transmissible syphilis in pregnant women. Reporting was incomplete; cases of late latent syphilis were excluded from the congenitally transmissible category (though transmission probably can occur from women during the late latent stage).2 Other cases would have been treated by obstetricians without referral to genitourinary medicine.2 If screening was stopped a minimum of 10 women a year with congenitally transmissible syphilis would be missed. These data are compatible with the 90-100 women newly diagnosed annually as having infectious or early latent syphilis5 and a recent increase in transmission of heterosexual syphilis in one urban locality outside London, where four maternal cases of transmissible syphilis would have been missed if antenatal screening had not been routine.8 It is estimated that the current universal screening policy would require 18 600 and 55 700 women (maximum numbers), respectively, to be screened to detect a case of a woman needing treatment and to prevent one case of congenital syphilis.2 Living in the Thames regions, being of a non-white ethnic group, or being born abroad are strong risk factors. The presence of cases without any of these risk factors, however, means a selective screening programme would miss cases, even if implementation was optimal. These data indicate that current screening prevents congenital syphilis and that some fetuses and infants would be placed at risk if routine screening was stopped. It also results in the detection of women with syphilis who require treatment and the prevention of further transmission of a highly infectious sexually transmitted disease. These data are contributing to the formulation of national policy by the National Screening Committee. 2 6