PHWR Public Health Weekly Report

Syphilis is a genital and systemic disease caused by infection with the bacterium Treponema pallidum. It is mainly classified as congenital or acquired syphilis, with acquired syphilis being further divided into primary, secondary, tertiary, and latent (early and late) syphilis [1]. Syphilis is currently a group 4 infectious disease under Paragraph 5, Article 2 (definitions) of the “Infectious Disease Control and Prevention Act” (IDCP Act), and a sexually transmitted infectious disease, as stipulated in Paragraph 10. Its incidence is monitored through designated surveillance agencies along with six other sexually transmitted infectious diseases (gonorrhea, chlamydia infection, chancroid, genital herpes simplex, condyloma acuminata, and human papillomavirus infection). The current National Notifiable Infectious Diseases (NNIDs) surveillance system is divided into sentinel and mandatory surveillance systems. Among these, the sentinel surveillance system refers to the designation of a surveillance agency to conduct regular and continuous medical and scientific surveillance for the occurrence of infectious diseases with relatively low severity, which are challenging to subject to mandatory surveillance due to the high frequency of cases. As of October, the requirement for sentinel surveillance of sexually transmitted infectious diseases mandates reporting within seven days following the confirmation of infectious diseases at 572 locations, including clinics, hospitals, and public health centers with urology and obstetrics and gynecology departments. Meanwhile, the mandatory surveillance system is operated by reporting individuals, such as doctors, who have to report the occurrence of a group 1 to 3 infectious disease to the local public health center immediately or within 24 hours of diagnosis. This system facilitates epidemiological investigations of individual patients and the accurate identification of outbreak patterns.

The surveillance system for syphilis has changed several times as follows: after the introduction of the sentinel surveillance system in 2001, it remained under the purview of sentinel surveillance until 2010. Then, in accordance with the revision of the NNIDs classification system in 2010, it transitioned to mandatory surveillance until 2019 and subsequently returned to sentinel surveillance from 2020 onward. As of 2023, the reporting criteria for syphilis encompass individuals diagnosed with primary, secondary, or congenital syphilis. After its restoration to sentinel surveillance, there were 354 reports in 2020, 337 in 2021, and 401 in 2022, a numerical increase of approximately 19% compared to the previous year. However, since the number of reported cases is small and the sentinel surveillance period overlaps with the coronavirus disease 2019 (COVID-19) pandemic period, limitations remain in determining the trend of increase or decrease in occurrence. According to the amendments in the “IDCP Act”, from January 1, 2024, syphilis will be elevated from a group 4 to a group 3 infectious disease and fall under mandatory surveillance system, thus, requiring all medical institutions to report syphilis cases within 24 hours of diagnosis. Therefore, this article aims to explain the background and necessity of the transition to mandatory surveillance for syphilis.

The key rationale for switching the surveillance for syphilis from sentinel to mandatory is as follows:

Firstly, this change stems from the relatively elevated risk of syphilis transmission. With the exception of vertical transmission from mother to child, syphilis primarily spreads through direct skin-to-skin contact with an infected person, such as via sexual intercourse. The risk of transmitting syphilis to sexual partners is high, approximately 51 to 64% [2], and unlike other sexually transmitted infections, such as gonorrhea, chlamydia, and trichomonas, even if a condom is used, infection could occur if areas not covered by a condom are exposed to Treponema pallidum [3].

Secondly, due to the protracted course of syphilis infection and the potential for severe complications in the absence of treatment, more meticulous management is required. If left untreated for a long period, bacteria can invade all tissues and organs of the body, which can lead to severe complications such as benign tertiary syphilis, cardiovascular syphilis, and neurosyphilis, as shown in Table 1 [4].

Table 1 . Third stage of syphilis infection.

	Gummas	Cardiovascular syphilis	Neurosyphilis
Time of occurrence	3 to 10 years of infection	10 to 25 years of infection	3 to 12 years of infection
Regions	The skin, bones and internal organs	Blood vessels connected the heart	Brain and spinal cord
Symptoms	Gummas are soft, destructive, inflammatory masses that are typically localized but may diffusely infiltrate an organ or tissue; they grow and heal slowly and leave scars.	Symptoms include brassy cough and obstruction of breathing due to pressure on the trachea due to vocal cord paralysis resulting from compression of the left laryngeal nerve, and painful erosion of the sternum and ribs or spine.	Inflammation of the arteries of the brain or spinal cord cause the cerebromeningitis. Symptoms may include headache, memory loss and insomnia. as well as behavioral abnormalities, poor concentration.

Thirdly, there is a need to eradicate congenital syphilis. The the Republic of Korea (ROK) supports the early detection of congenital syphilis through prenatal testing, as the disease can be completely cured when detected and treated early. However, syphilis continues to exist and so intensive management is imperative. Congenital syphilis usually occurs after 4 months of pregnancy, develops within 2 years of birth, and shows similar symptoms to adult secondary syphilis. Fetuses of mothers infected with syphilis are at high risk of premature birth and stillbirth, and even after birth, newborns infected with Treponema pallidum may develop symptoms such as hearing loss, hydrocephalus, optic nerve atrophy, and mental retardation [5].

Fourthly, given the significant economic and psychological burden associated with post-treatment follow-up for syphilis, mandatory surveillance is necessary to curtail its prevalence. Following syphilis treatment, patients should visit the hospital periodically to monitor clinical symptoms and serum antibody titers. This helps determine the effectiveness of the treatment, as it takes approximately 1 to 2 years for the serum antibody titer to decrease to levels indicative of a complete cure [6].

Finally, this shift in surveillance serves as a preemptive response to the increasing trend of syphilis in neighboring countries. Japan, Taiwan, and China, all of which are conducting mandatory surveillance for syphilis, have recently seen an increase in the number of syphilis cases. This raises concerns about the potential importation of syphilis into the ROK, as international human and material exchanges are expected to expand after the COVID-19 pandemic period. Consequently, it is necessary to proactively fortify the surveillance system.

Recently, with the aim of eradicating syphilis, the World Health Organization (WHO) set a goal of reducing the incidence of syphilis by 90% by the year 2030, in comparison to the rates observed in 2020. The WHO has also underscored the importance of strengthening prevention and management policies to achieve this goal [7]. To systematically prevent and manage sexually transmitted infectious diseases, including syphilis, the ROK established prevention and management measures for sexually transmitted infectious diseases in 2022, setting the mid-to-long-term goal of eradicating adult syphilis (primary and secondary syphilis) and congenital syphilis.

According to the WHO, as of 2020, approximately 7 million new cases of syphilis were reported per year. Exploring the syphilis surveillance systems in neighboring countries, as shown in Table 2, in the United States, 133,945 cases of syphilis occurred in 2020, an increase of 6.8% compared to the previous year; and in the European Union/European Economic Area, 35,039 cases occurred in 2019, an increase of 3.3% compared to the previous year. In Taiwan, a neighboring country, the number of cases increased from 9,413 in 2021 to 9,675 in 2022, while in China they increased from 480,020 in 2021 to 497,934 in 2022, that is an increase of approximately 3%, compared to the previous year. Notably, Japan exhibited a rapid increase, with cases surging by 60% in a single year, from 7,983 cases in 2021 to 12,966 cases in 2022 (Figure 1).

Figure 1. The reported syphilis case counts of the neighboring countries from 2020 to 2022

Table 2 . Syphilis monitoring system of the neighboring countries.

	Responsible agency	monitoring system	Report period
United States	CDC	Mandatory	weekly
The United Kingdom	PHE	Sentinel	quarterly
Japan	NIID	Mandatory	weekly
China	China CDC	Mandatory	monthly

CDC=Centers for Disease Control and Prevention; PHE=Public Health England; NIID=National Institute of Infectious Diseases..

As evident from the aforementioned data, there is a discernible global trend of increasing incidence of syphilis cases. However, ROK’s current surveillance system has some limitations in accurately predicting these trends. Given the high risk of infection, the potential for severe complications, and the possibility of long-term transmission, syphilis requires the establishment of comprehensive policies spanning prevention-diagnosis-treatment-chronic management. However, the current sentinel surveillance system faces constraints in gathering information beyond the scope of sample reports, making it challenging to identify the overall occurrence situation. Additionally, detailed analysis of patients’ demographic characteristics and disease stages is also difficult. Accordingly, the “IDCP Act”, amended on August 8, 2023, has expanded the scope of syphilis surveillance to the entire population. This expansion was designed to help accumulate sufficient statistical data for analysis, such as trends in occurrence, while at the same time establishing a basis for identifying the cause of occurrence and disease characteristics through epidemiological investigation.

Mandatory surveillance for syphilis will be implemented from January 1, 2024, and the scope of reporting will be expanded to five types, including early latent syphilis, which is likely to be transmitted, and tertiary syphilis, which progresses to severe disease, in addition to the current three types (primary and secondary syphilis, and congenital syphilis). Given that sentinel surveillance only identifies approximate occurrence trends by counting the number of patients based on sample reports, it is difficult to determine the exact incidence rate. In addition, the reported contents are limited to basic information such as sex, age, diagnosis date, and reporting date, thereby constraining the ability to discern the disease characteristics of syphilis patients in the ROK. Transitioning to mandatory surveillance entails reporting all identified cases, facilitating an objective overview of the overall occurrence of syphilis in the ROK. This shift also enables the collection of a wide range of information, including demographic characteristics, stage and main symptoms, exposure route, and contacts of individual patients through epidemiological investigations. Therefore, this transition is anticipated to facilitate the development of more comprehensive prevention and management measures. Key changes associated with the shift of syphilis within the infectious disease classification are depicted in Figure 2.

Figure 2. The comparisons according to the surveillance system changes
KDCA=The Korea Disease Control and Prevention Agency; ID=identification; Epi=epidemiological.

The transition to mandatory surveillance of syphilis, as mandated in this amendment of the “IDCP Act”, aims to identify the overall occurrence and trends of syphilis in the ROK by expanding the scope of syphilis reporting and epidemiological investigation to all populations. Further, by collecting information on individual patients, it aims to establish a foundation for a detailed analysis of syphilis demographic characteristics and disease stage. The Korea Disease Control and Prevention Agency (KDCA) plans to continuously establish and promote evidence-based prevention and management policies to eradicate adult and congenital syphilis and strengthen the surveillance system of infectious diseases.

In the future, when researchers or the general public use syphilis-related statistical data published by the KDCA, it is important that they exercise caution in interpreting the results. This is because disparities in the number of reported cases across different surveillance systems by year may potentially lead to misinterpretations when directly comparing syphilis incidence statistics from various years. Thus, care should be taken when interpreting statistics and both the annual surveillance system and reporting scope should be considered.

Ethics Statement: Not applicable.

Funding Source: None.

Acknowledgments: We would like to extend sincere gratitude and appreciation to Prof. Seungju Lee, the Dean of the Korean Association of Urogenital Tract Infection and Inflammation for his support, continuous guidance and careful suggestions.

Conflict of Interest: The authors have no conflicts of interest to declare.

Author Contributions: Conceptualization: SJW. Methodology: SJW. SJK, SSJ. Supervision: HSK, SNM. Writing – original draft: SJW. Writing – review & editing: SJW, HSK. SNM.