In 2007, the WHO set the goals of eradicating congenital syphilis with an incidence of less than 50 cases per 100,000 live births, as well as providing prenatal screening and adequate treatment, if necessary, to at least 95% of pregnant women (9, 27). The aim is to achieve this in 80% of all countries by 2030. Between 2012 and 2016, the incidence of syphilitic infections in pregnant women remained virtually unchanged, with a WHO estimate of 700 and 690 cases per 100,000 pregnant women, respectively. Between 2012 and 2016, the estimated global incidence of congenital syphilis also decreased from 539 to 473 cases per 100,000 live births. This 12% decrease may reflect a progress; however, the rates are still far from the target set by the WHO (27).

Although the incidence is mostly decreasing worldwide, it is unfortunately not the case everywhere. In the United States, the rate of reported congenital syphilis has increased sharply since 2012 (11, 12). In fact, there has been a 477% increase between 2012 and 2019, with the incidence of congenital syphilis rising from 8.4 to 48.5 cases per 100,000 live births (31). Four possible explanations are the parallel increase in primary and secondary syphilis cases in young women of childbearing age, which almost tripled between 2015 and 2019 (3, 12, 13), the lack of prenatal screening and adequate treatment, as well as syphilitic reinfections during pregnancy (13, 32, 33). In fact, in 2019, 60% of congenital syphilis cases in the United States resulted from a lack of prenatal screening, or from inadequate treatment of pregnant women with established diagnoses (12). In addition, several studies observed considerable racial and ethnic disparities, with higher rates found among minorities and vulnerable populations, such as Native populations, African Americans or Hispanic individuals (3, 12–14). Some studies also observed higher rates in economically disadvantaged populations, drug users, or individuals released from incarceration (13, 15).

Similar observations were reported in neighboring countries, including Canada, with a 10- to 15-fold increase of congenital syphilis between 2016 and 2020 (16). Once again, the populations identified as most at risk were Native American and economically challenged patients: they face a lack of access to care, longer delays between diagnosis and treatment with many missed opportunities (16, 34). Mexico was also affected by a 6-fold increase in the number of congenital syphilis cases between 2010 and 2019 (17).

In South America, each country uses its own definition of congenital syphilis and notification type may vary. Cases are probably underestimated (35). Brazil is particularly affected, with an alarming increase from 143 to 861 cases per 100,000 live births between 2002 and 2016 (19); a slight decrease to 770 cases per 100,000 live births was nevertheless reported in 2020 (36). This large number of cases can be explained by the lack of access to rapid tests or treatment in certain regions (36). Despite the extent of Brazilian health system and community participation in the health sector, there is still insufficient prenatal screening and many missed opportunities with an increase in untreated or inadequately treated cases (19, 37). A study conducted in a hospital in the North East (Conceiçao) between 2008 and 2018 showed that 61% of pregnant women diagnosed with syphilis received inadequate treatment or were not treated at all (20). Similarly to North America, indigenous populations remain the most affected (36).

Other South American countries, such as Paraguay, raise concerns, with an incidence of 197 cases per 100,000 live births in 2018 according to reports; however, the WHO estimates a 9-fold discrepancy between estimated and reported cases, with an estimate of 1792 cases per 100,000 live births. A 1.6-fold increase in cases between 2018 and 2020 has been noted (38).

Concerning developing and emerging countries, the African continent remains the most affected area, with over 60% of the worldwide congenital syphilis cases between 2012 and 2016. This can be explained by the high maternal prevalence and the lack of access to antenatal care (6, 27).

Elsewhere, developed countries such as Japan, Australia and New Zealand have also described outbreaks of congenital syphilis, with an incidence of 9.4 cases per 100,000 live births in the latter between 2018 and 2020 (39). In Japan, the incidence is also gradually increasing (from 0.4 to 1.4 cases per live birth between 2012 and 2016), raising a public health concern (18). Again, the most at-risk populations include the most vulnerable populations (drug users, etc.) (17, 39). In Australia, it has been described that the incidence of congenital syphilis is up to 20 times higher in the indigenous populations than in non-indigenous populations (40).

However, there are also countries with declining incidence rates. In China, the beginning of the millennium (2000–2011) was marked by an almost 25-fold increase in congenital syphilis cases, prompting the country to implement an action plan to improve screening and treatment of the disease, doubling the number of pregnant women screened for syphilis between 2011 and 2018. During the same period, the incidence of congenital syphilis decreased significantly from 91.6 to 18.4 cases per 100,000 live births; however, the number of syphilis cases diagnosed in pregnant women continues to increase each year (41, 42). This example shows that implementing a national action plan can be effective.

Finally, the only continent to have reached the goal set by the WHO for the elimination of the disease is Europe (27). The number of congenital syphilis cases reported in the European Union has decreased overall since 2005, despite an increasing curve in recent years, according to ECDC’s online interactive Surveillance Atlas of Infectious Diseases (21, 22). Indeed, in 2018, for the first time since 2013, the number of reported cases increased, with 60 confirmed cases of congenital syphilis in 23 European Union countries, representing an incidence of 1.6 per 100,000 live births (22, 43). The latest available data date from 2021, with an incidence of 1.8 cases per 100,000 live births (44). These data illustrate the impact of measures taken by governments in prenatal screening programs for the disease; covering 98% of pregnant women in 2016–2017, the European Union had the highest rate in the world (1). However, data are still underestimated, and underreporting is highly probable (21, 22). On a smaller scale, there is a wide variation among European countries, with incidence ranging from 0.1 to 39.8 cases per 100,000 live births in some years (22, 23). Eastern European countries seem to be the most affected, especially Bulgaria, with an incidence of 20 cases per 100,000 live births recorded in 2016. In the same year, the second and third place were held, respectively, by Poland and Romania (21). In Bulgaria, the number of cases continued to increase with a 250% rise between 2017 and 2019 (17). Once again, the most vulnerable populations, such as migrant women, sex workers and drug users, are mostly affected; social marginalization and exclusion delay access to care (8, 22, 45).

In Switzerland, the incidence varies greatly from year to year. Between 2013 and 2022, it varied from 0 to 8.14 cases of syphilis per 100,000 inhabitants under the age of 1, with an average incidence of 1.6 over the last 10 years (2). The notification system has been modified in recent years: notably, stillbirths and abortions associated with syphilis infection have been notified since 2019. Physicians notify stillbirths and abortions in a woman with positive syphilis test for which no other etiology was found (46). However, the epidemiological data are not very detailed and may be underestimated since congenital syphilis is reported in the same form as all syphilis. It has been shown that 20% of pregnant women in Switzerland have not been screened for syphilis (47). Compared to the general Swiss population, studies have reported that undocumented migrants present later to antenatal care and have a higher risk of sexually transmitted infections in the context of risky behavior (48). A 10-year study at the University Hospital of Zurich has shown that among nine pregnant patients with a positive treponemal test, eight were immigrant patients (49).

It is important to understand where the failures of a developed country’s healthcare system like Switzerland come from, why certain vulnerable populations are left out, despite theoretical measures to include them.

Because of its strong socio-economic position, Switzerland is exposed to both legal and illegal migration. It is estimated that Switzerland has up to 100,000 undocumented migrants: many are middle-aged women from Latin America, Eastern Europe, Asia and North and West Africa (48).

There are three main groups of migrants in the country:

The response of the Swiss healthcare system varies greatly, with different policies for each canton.

Only 2 of the 26 Swiss cantons (Geneva and Vaud) have established primary care services for undocumented migrants, providing free or inexpensive access to health facilities. In the other cantons, these primary care services are provided by non-governmental organizations or, in some cases, exist only in the emergency departments of public hospitals (48, 51).

A study of the undocumented migrant population in the canton of Geneva shows that only 16% are covered by required health insurance (52).

In a situation of distress, the Swiss Constitution guarantees that patients receive essential care and are treated in a manner consistent with human dignity, regardless of their insurance cover (53).

Despite the theoretical measures, the Swiss healthcare system has many limitations for undocumented migrant patients.

First, we note a cost barrier. In Switzerland, health insurance fees and co-payments are very high, which sometimes leads to insurance coverage being waived, care being forgone, or treatment being delayed.

Additionally, undocumented individuals may also fear being reported and avoid contact with public institutions as much as possible. In case of non-payment, despite medical confidentiality, insurers try to recover the money, which increases the risk of being discovered.

Furthermore, migrants are likely to be isolated and face language barriers, resulting in a lack of information on access to healthcare in general, despite the work of some associations that carry out medical prevention at strategic points.

Another difficulty that can be encountered by migrants is filling out administrative documents. The administrative difficulties to obtain health insurance are considerable: insurance companies often make it difficult for them to take out a policy, with refusals (due to lack of knowledge of the law) or unfeasible requests (e.g., a postal address or a residence permit). In addition, the language barrier increases the difficulty of understanding administrative documentation and procedures.

Finally, although emergency care is provided, chronic health problems requiring continuity of care on an outpatient basis are not necessarily covered in all cantons (48, 51).