Global Estimates of Syphilis in Pregnancy and Associated Adverse Outcomes: Analysis of Multinational Antenatal Surveillance Data

Abstract

Using multinational surveillance data, Lori Newman and colleagues estimate global rates of active syphilis in pregnant women, adverse effects, and antenatal coverage and treatment needed to meet WHO goals.

Abstract

Background

The World Health Organization initiative to eliminate mother-to-child transmission of syphilis aims for ≥90% of pregnant women to be tested for syphilis and ≥90% to receive treatment by 2015. We calculated global and regional estimates of syphilis in pregnancy and associated adverse outcomes for 2008, as well as antenatal care (ANC) coverage for women with syphilis.

Methods and Findings

Estimates were based upon a health service delivery model. National syphilis seropositivity data from 97 of 193 countries and ANC coverage from 147 countries were obtained from World Health Organization databases. Proportions of adverse outcomes and effectiveness of screening and treatment were from published literature. Regional estimates of ANC syphilis testing and treatment were examined through sensitivity analysis. In 2008, approximately 1.36 million (range: 1.16 to 1.56 million) pregnant women globally were estimated to have probable active syphilis; of these, 80% had attended ANC. Globally, 520,905 (best case: 425,847; worst case: 615,963) adverse outcomes were estimated to be caused by maternal syphilis, including approximately 212,327 (174,938; 249,716) stillbirths (>28 wk) or early fetal deaths (22 to 28 wk), 91,764 (76,141; 107,397) neonatal deaths, 65,267 (56,929; 73,605) preterm or low birth weight infants, and 151,547 (117,848; 185,245) infected newborns. Approximately 66% of adverse outcomes occurred in ANC attendees who were not tested or were not treated for syphilis. In 2008, based on the middle case scenario, clinical services likely averted 26% of all adverse outcomes. Limitations include missing syphilis seropositivity data for many countries in Europe, the Mediterranean, and North America, and use of estimates for the proportion of syphilis that was “probable active,” and for testing and treatment coverage.

Conclusions

Syphilis continues to affect large numbers of pregnant women, causing substantial perinatal morbidity and mortality that could be prevented by early testing and treatment. In this analysis, most adverse outcomes occurred among women who attended ANC but were not tested or treated for syphilis, highlighting the need to improve the quality of ANC as well as ANC coverage. In addition, improved ANC data on syphilis testing coverage, positivity, and treatment are needed.

Please see later in the article for the Editors' Summary

Editors' Summary

Background

Syphilis—a sexually transmitted bacterial infection caused by Treponema pallidum—can pass from a mother who is infected to her unborn child. Screening pregnant women for syphilis during routine antenatal care by looking for a reaction to T. pallidum in the blood (seropositivity) and then treating any detected infections with penicillin injections has been feasible for many years, even in low-resource settings. However, because coverage of testing and treatment of syphilis remains low in many countries, mother-to-child transmission of syphilis—“congenital syphilis”—is still a global public health problem. In 2007, the World Health Organization (WHO) estimated that there were 2 million syphilis infections among pregnant women annually, 65% of which resulted in adverse pregnancy outcomes: the baby's death during early or late pregnancy (fetal death and stillbirth, respectively) or soon after birth (neonatal death), or the birth of an infected baby. Babies born with syphilis often have a low birth weight and develop problems such as blindness, deafness, and seizures if not treated.

Why Was This Study Done?

In 2007, WHO launched an initiative to eliminate congenital syphilis that set targets of at least 90% of pregnant women being tested for syphilis and at least 90% of seropositive pregnant women receiving adequate treatment by 2015. To assess the initiative's progress and to guide policy and advocacy efforts, accurate global data on the burden of syphilis in pregnancy and on associated adverse outcomes are needed. Unfortunately, even in developed countries with good laboratory facilities, definitive diagnosis of congenital syphilis is difficult. Estimates of the global burden can be obtained, however, using mathematical models. In this study, the researchers generate global and regional estimates of the burden of syphilis in pregnancy and associated adverse outcomes for 2008 using a health services delivery model.

What Did the Researchers Do and Find?

The researchers developed a mathematical model to estimate the number of syphilis-infected pregnant women in each country and in each region, and to estimate the regional and global numbers of adverse pregnancy outcomes associated with syphilis. They used national syphilis seropositivity data and information on antenatal care coverage from WHO and estimates of the effectiveness of screening and treatment from published literature. Using these data and their model, the researchers estimated that, in 2008, 1.4 million pregnant women, 80% of whom had attended antenatal care services, had an active syphilis infection. Assuming a scenario in which the percentage of pregnant women tested for syphilis and adequately treated ranged from 30% for Africa and the Mediterranean region to 70% for Europe (a scenario defined in consultation with WHO advisors), the researchers estimated that maternal syphilis caused 520,000 adverse outcomes in 2008, including 215,000 stillbirths or fetal deaths, 90,000 neonatal deaths, 65,000 preterm or low birth weight infants, and 150,000 infants with congenital disease. About 66% of these adverse effects occurred in women who had attended antenatal care but were either not tested or not treated for syphilis. Finally, the researchers estimated that in 2008, clinical services averted 26% of all adverse outcomes.

What Do These Findings Mean?

These findings, which update and extend previous estimates of the global burden of congenital syphilis, indicate that syphilis continues to affect a large number of pregnant women and their offspring. The current findings, which cannot be directly compared to previous estimates because of the different methodologies used, are likely to be affected by the accuracy of the data fed into the researchers' model. In particular, the data on the percentage of the population infected with syphilis in individual countries used in this study came from the HIV Universal Access reporting system and may not be nationally representative. Nevertheless, these findings suggest that syphilis continues to be an important cause of adverse outcomes of pregnancy, partly because pregnant women often do not receive syphilis screening and prompt treatment during routine antenatal care. The researchers recommend, therefore, that all countries should ensure that all pregnant women receive an essential package of high-quality antenatal care services that includes routine and easy access to syphilis testing and treatment. Congenital syphilis, they conclude, can only be eliminated if decision-makers at all levels prioritize the provision, quality, and monitoring of this basic antenatal care service, which has the potential to reduce infant mortality and improve maternal health.

Additional Information

Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001396.

• The World Health Organization provides information on sexually transmitted diseases, including details of its strategy for the global elimination of congenital syphilis, the investment case for the elimination of mother-to-child transmission of syphilis, and regional updates on progress towards elimination (some information is available in several languages)

• The Pan American Health Organization provides information on efforts to eliminate congenital syphilis in Latin America (in English and Spanish), and the Asia-Pacific Prevention of Parent-to-Child Transmission Task Force provides information on efforts to eliminate congenital syphilis in Asia Pacific

• The US Centers for Disease Control and Prevention has a fact sheet on syphilis (in English and Spanish)

• The UK National Health Service Choices website also has a page on syphilis

• MedlinePlus provides information on congenital syphilis and links to additional syphilis resources (in English and Spanish)

• The London School of Hygiene and Tropical Medicine provides a toolkit for the introduction of rapid syphilis tests

• Haiti: Congenital Syphilis on the Way Out is a YouTube video describing the introduction of rapid diagnostic tests for syphilis in remote parts of Haiti