The highest incidence of syphilis in the general population was observed in 2019 with 6.09 cases per 100,000 inhabitants, compared to 2.03 cases in 2010, with an average annual increase of 0.336 cases per 100,000 inhabitants (CI95% 0.180–0.492, p = 0.001). Since 2012, men had a higher incidence of syphilis than women; the average increase among men was 0.482 cases per 100,000 inhabitants (CI95% 0.303–0.660, p < 0.001), compared to the increase among women that was 0.178 cases per 100,000 inhabitants (CI95% 0.017–0.339, p = 0.034), this difference was statistically significant (p = 0.010). An increase of congenital syphilis was observed, a rate of 2.93 per 100,000 newborns in the year 2014, up to 17.28 in the year 2019, with an average annual increase of 1.693 per 100,000 newborns (CI95% 0.986–2.394, p < 0.001), as shown in Fig. 1.
Among women, the highest incidence occurred in the 20–24 years-old group with 16.77 cases per 100,000 inhabitants in 2019 and an annual increase of 0.438 per 100,000 inhabitants (CI95% 0.062–0.813; p = 0.028), followed by 15–19 years-old group with an incidence of 12.7 cases per 100,000 inhabitants in 2019 and an average annual increase of 0.693 (CI95% 0.191–1.194; p = 0.012). Among men, the increase in incidence was concentrated in the 20-24-year-old group with a rate of 14.89 cases per 100,000 inhabitants in 2019, with an annual increase of 0.786 per 100,000 inhabitants (CI95% 0.653–1.505; p < 0.001), followed by the group of 25–44 years with an incidence of 13.93 cases per 100,000 in 2019, with an annual increase of 0.991 cases per 100,000 (CI95% 0.462–1.521, p = 0.002), as shown in Fig. 2.
We reported a constant increase of new cases of congenital syphilis, 62 cases in the year 2010, 83 cases in the year 2015, and 372 cases in the year 2019. The states with the highest number of congenital syphilis cases in 2010 were Baja California, Colima, Chihuahua, Nuevo León, and Sonora, which reported between 6 and 17 cases; while in the year 2019 Baja California, Jalisco, Sinaloa, Sonora, and Tamaulipas presented between 20 and 79 cases of congenital syphilis. In addition, of the 32 states of Mexico, 16 did not report congenital syphilis cases in 2010, on the other hand, three states did not report congenital syphilis cases in 2019. The states of Campeche, Hidalgo, Morelos, Oaxaca, and Tlaxcala were two or fewer congenital syphilis cases from 2010 to 2019, as shown in Fig. 3.
The number of cases of congenital syphilis was correlated with the incidence of syphilis among women from 2010 to 2019 (r2 = 0.787, p < 0.001), however, this correlation is higher when stratifying by age. Among women aged 15–19 years, each increase in an incidence unit showed an average increase of 36 new cases of congenital syphilis (slope 36.1, CI95% 26.5–45.8, r2 = 0.904; p < 0.001); among the group of women aged 20–24, this increase was an average of 30 cases per year (slope 30.4, CI95% 24.8–36.0, r2 = 0.952; p < 0.001), as shown in Fig. 4. The correlation between syphilis and congenital syphilis by state of the Mexican Republic was evaluated, the information from 2019 of women aged 20–24 years was used, finding an r2 = 0.621; p < 0.001. The seven states that reported an incidence of congenital syphilis greater than 40 cases per 100,000 live births are the same states that presented an incidence of syphilis greater than 40 cases per 100,000 women. States such as Morelos and Quintana Roo, reported a higher incidence of syphilis and a lower incidence of congenital syphilis, in contrast, states such as San Luis Potosí, Tabasco and Veracruz, reported a higher incidence of congenital syphilis and a lower incidence of acquired syphilis, such as shown in Fig. 5.
The general mortality due to congenital syphilis in children under 1 year of age in Mexico was 0.02 per 100,000 children for the year 2012, and 0.01 for the years 2015, 2016, and 2017; for the years 2010, 2011, 2013, and 2014 we did not find information. In the review of deaths from congenital syphilis, 62 deaths were found between the years 2010 to 2017, the lowest number being in the years 2010 (5 deaths) and 2014 (1 death) and the highest in the years 2011 (10 deaths), 2015 (12 deaths) and 2017 (10 deaths). Considering the total number of deaths between 2010 and 2017 by state, the states of Baja California (7), Chihuahua (5), Jalisco (6), Sinaloa (5) and Veracruz (5), are those that presented the highest number of deaths, in contrast the states of Baja California Sur, Campeche, Guerrero, Hidalgo, Puebla, Quintana Roo, San Luis Potosí, Tlaxcala, Yucatán and Zacatecas, did not report any death from congenital syphilis during the period analyzed.