ANC: Antenatal Care; AOR: Adjusted Odds Ratio; CI: Confidence Interval; COR: Crude Odds Ratio; SPSS: Statistical Package for the Social Sciences; STI: Sexually Transmitted Infections; VDRL: Venereal Disease Research Laboratory test

The term "sexually transmitted infection (STI)" refers to a pathogen that causes infection through sexual contact, whereas the word "sexually transmitted disease" refers to an identifiable clinical condition that has arisen from an infection [1,2]. Sexually transmitted infections are among the leading causes of sickness worldwide, with far-reaching health, social, and economic effects. Because of the quantity and possible difficulties of sexually transmitted illnesses, they are of public health relevance. They have a disproportionate impact on mothers' health and social well-being by having a considerable impact on their reproductive capacity [3].

Untreated syphilis is a disease that lasts for many years and is classified into two stages: Early syphilis includes primary syphilis, secondary syphilis, and early latent syphilis, whereas late syphilis includes late latent syphilis and tertiary syphilis [2].

Adult syphilis symptoms vary according to stage. Signs and symptoms of the main stage include a single or multiple sores at the location where syphilis entered the body (initial stage of syphilis). Sores that are firm, round, and painless are prevalent (though not always). During the secondary stage, skin rashes and/or mucous membrane lesions, such as sores in mouth, vagina, or anus, occur. The absence of visible evidence or symptoms of syphilis characterizes the latent period. Tertiary syphilis is exceedingly serious and can appear 10-30 years after the initial infection. Tertiary syphilis damages internal organs and can result in death [1,4].

Syphilis has an average incubation period of 3 weeks (from exposure to the development of initial signs or symptoms), although it can be as little as 10 days or as long as 90 days. Serologic test results show negative during the incubation period, and the patient is not deemed infectious. However, without syphilis post-exposure treatment, those with incubating infection will develop primary syphilis lesions, a highly infectious stage of illness [1].

STIs are a major public health issue around the world, impacting quality of life and causing significant morbidity and mortality. Congenital syphilis imposed a significant morbidity and death burden [5]. Report from Centers for Disease Control during 2012–2016, showed the number of reported cases of syphilis among pregnant women increased by 55% (9,551 to 14,838), and the number of cases among pregnant women was increased by 61%, (1,561 to 2,508) [6]. The burden of syphilis among pregnant women in sub-Saharan Africa was 2.9%. Syphilis infection among pregnant women has increased in East and Southern African regions (3.2%) [7]. In Ethiopia the magnitude of syphilis infection was in the ranged of 1.1% to 5.1% [8-11].

Multiple sexual partners, previous history of abortion, previous history of STI, substance use, starting first sexual practice before the age of 18 years, sexual partners’ history of STI were risk factors of syphilis infection [11-13].

At any phase of syphilis infection, the infection can be transmitted to a fetus during pregnancy and can result in adverse pregnancy outcome or severe birth defects [5]. Syphilis continues to be a major cause of pregnancy loss and adverse pregnancy outcome among mothers who do not receive antenatal syphilis screening and treatment during pregnancy. Adverse pregnancy outcome such as stillbirths, and preterm were attributable to maternal syphilis [14]. Adverse pregnancy outcome like stillbirth, preterm birth, and low birth weight were related with untreated maternal syphilis during pregnancy [15].

Mother-to-child transmission of syphilis (congenital syphilis) is frequently fatal to the fetus if maternal infection is not detected and treated early enough in pregnancy. The fetus can be easily treated, and the danger of poor effects to the fetus is negligible if the mothers receive adequate treatment throughout early pregnancy [16]. Early detection and treatment of syphilis in pregnant women is critical for treating the infection and minimizing adverse pregnancy outcomes such as fetal and neonatal death [5].

Ethiopia has remarkable progress in screening and treatment of STIs like syphilis especially for pregnant women. Since mother to child transmission at birth is the most common way of transmission of syphilis infection, identifying syphilis among pregnant women in the area is very important for the prevention of vertical transmission to the new born [3].

Despite the implementation of different guidelines to control STIs in Ethiopia, the burden of syphilis during pregnancy is persisting. Although some studies were conducted in different parts of Ethiopia on syphilis infection among pregnant women, less common determinants were identified. This variation could be due to study design in which cross-sectional study design was generally used. But there was a limited case control study on determinants of syphilis infection at the study area. Therefore, this study was aimed to address this gap by using case control study design to identify syphilis determinants among pregnant women attending ANC at Public hospital, South West Shoa.

Study area and study period

The study was carried out at public hospitals in South West Shoa Zone, Oromia region, Ethiopia. Southwest Shoa Zone is located 114 KM to the south of Addis Ababa. Southwest Shoa Zone comprised five government hospitals named Tullu Bollo General Hospital, Waliso General Hospital, Ameya Primary Hospital, Bantu Primary Hospital, Leman Primary Hospital, and one non-government hospital called Lukas Catholic Hospital which is found in Waliso, the capital city of the South West Shoa Zone. Last year's annual ANC reports were as follows: from Tullu Bollo general hospital (882), 804 were non-reactive and 78 were reactive, from Woliso General Hospital (918), 824 were non-reactive and 90 were reactive, from Ameya primary hospital (366), 294 were non-reactive and 72 were reactive, from Bantu primary hospital (432) 378 were non-reactive and 54 were reactive, and from Leman primary hospital (420) 360 were non-reactive and 66 were reactive.

Study period

The study was conducted in South West Shoa zone at five public hospitals from March 10, 2023–May 10, 2023.

 Study design

 Institutional based unmatched case control study design was conducted.

Source population

All pregnant women attending ANC at Public hospital in South West Shoa Zone.

Study population

Pregnant women those attending routine ANC follow up at five public hospitals in South West Shoa zone and tested positive for syphilis during ANC visits were considered as cases in this study. Pregnant women who were attending routine ANC follow up at five public hospitals in South West Shoa zone and tested negative for syphilis tests during laboratory services at ANC visits were considered as control group.

Inclusion criteria

All pregnant mothers who had attended ANC at five public hospitals in South West Shoa zone and tested positive for syphilis tests during the study period were included. Those who were reported negative for the syphilis tests during the study period were also included.

Exclusion criteria

Pregnant mothers who had incomplete documentation during their ANC visits, and those who were critically ill and unable to communicate were excluded from the study.

Sample size determination

Sample size was determined by using Open Epi info version 7.2.5 using double population proportion exposure difference formulas by considering major determinants of syphilis infection such as history of multiple sexual partners and alcohol use [17], and a history of sexually transmitted infections and used a substance [13]. The confidence level was set at 95%, power at 80%, and ratio of cases to controls was 4. The final sample size calculated after adding 10% of non-response rate was 236. But to make 1:4 proportion of cases to controls, a total sample size of 240 was taken (48 cases and 192 controls).

Sampling technique and procedure

The number of study participants from each hospital was determined by proportional allocation to population size by using an average of two months from last year’s ANC report taken from each hospital. To allocate sample size of the control group to each hospital an average of two months of non-reactive syphilis test reports from the previous year was used. Then the average two months non-reactive syphilis report of all hospitals from last year (N) was divided by total sample size of the control group (n) to obtain the interval (K), K=N/n = 444/192= 2.3 ~2. The first study participant of the control group was determined by lottery method. Then, by using a systematic random sampling method, the data collectors had interviewed pregnant mothers every 2 days until the required sample size was obtained and case group was selected by convenience sampling technique (all mothers who were reactive for syphilis test) until 48 samples were reached (Figure 1).

Study variables

Dependent variable: Syphilis infection

Independent variable:

Socio-demographic characteristics: Age, residence, marital status, occupational status, and educational status.

Obstetrics characteristics: Abortion, still birth, ANC, parity, and multiple pregnancy.

Lifestyle related factors: Multiple partners, age at sexual intercourse started, substance use, and alcohol consumption.

Sexual transmitted disease history related factors: History of STI.

Operational definition

Cases: Individuals who have the outcome of interest. Those who have syphilis infection in this study.

Controls: Individuals who do not have the outcome interest. Those who do not have syphilis infection in this study [18].

Data collection instrument and technique

A structured questionnaire was adapted after reviewing different kinds of literature. The questionnaire consisted of 7 items of socio-demographic characteristics, 9 items of obstetrics related factors, and 3 items of medical history related factors, 6 items of lifestyle related factors, and 2 items of serological test. Pregnant women who were tested and found reactive for RPR reagent during their ANC follow up were diagnosed as positive for active syphilis, while those who were nonreactive were determined to be negative for active syphilis [19]. The questionnaire contains 5 parts and 27 items.

The data were collected using a pre-tested structured face-to-face interview questionnaire and chart review prepared in Afan Oromo. The data were collected by four BSc midwives who are fluent in the local language and supervised by two senior midwives.

Data quality control (assurance)

To ensure quality, tools were adapted from related articles, pre-tested on 5% of the study participants at Holeta Primary Hospital. To ensure the consistency of the questionnaires, the English version was translated into Afan Oromo and again retranslated back to English by an expert language translator. The data collectors and supervisors were recruited from outside the study hospitals to minimize bias and training was given regarding data collection procedure, tools, the purpose of study, and ethical consideration. Data collectors were strictly supervised. At the end of each day, the questionnaire was reviewed and checked for completeness by the supervisors, and necessary corrections were made.

The collected data were checked for completeness by the supervisors before data entry into the application and each approved questionnaire was properly coded and assigned a unique Identification number before being entered for analysis. Data were entered into Epi info to minimize errors, check duplicated entries, and to design a skipping pattern. Outlier and missed data were checked before data analysis using SPSS version 25.

Data processing and analysis

Multi co-linearity was checked by using variance inflation factors, the maximum value for variance inflation factors was 1.47, which is by far lower than tolerable cut off point 10 and tolerance test showed a range of 0.676-0.951. The goodness of fit (GOF) of the model was checked using Hosmer–Lermeshows GOF test. The p value of Hosmer –Lermeshows GOF test of our model is 0.78, indicating that the model was a good fit.

Descriptive analysis (like frequencies, percentages, means, and standard deviation) and inferential analysis was done. The bivariate and multivariable logistic regression analysis was done. A p-value <0.25 associated with study variables were transferred to multiple logistic regression models. AOR (adjusted odds ratio) with 95% confidence interval was computed, and the p-value <0.05 was considered statistically significant in the multivariable logistic regression analysis. The results were presented using text, tables, and charts.

Ethical consideration

An ethical clearance letter was obtained from Ambo University College of Health Science Ethical Review committee with Ref. number AU/PGC/630/2015 on 15/03/2023 and a supportive letter was obtained from the College of Health Science. Then, a permissions letter was obtained from the Zonal Health Bureau, South West Shoa Zone, and permissions for data collection were obtained from all hospitals. Verbal informed consent was obtained from the study participants before the interview. The study participants were informed about the purpose of the study and the importance of their participation in the study by providing information that may help in assessing syphilis infection services. The study participants were also informed that they could choose to skip or only partially answer questions they were uncomfortable with, and they could also stop at any time if they want to do so. The interview was conducted in a separate area with protected privacy. After getting consent & their willingness to participate in the study, they were provided with the questionnaire and oriented on how to respond to the questions.

Data was collected from 240 participants, and out of which 235 women had completed the interview, resulting in a response rate of 97.92%.

Socio-demographic characteristics of the respondents

Age of the respondents ranged from 16-36 years with a mean age of 26.93 years (26.93 ± 3.95). Twenty two women (46.8%) from case group and 78 women (41.5%) from control group were between 24-29. About half of the cases 23 (49%), and 95 (50.5%) of controls had completed a diploma or higher educational status (Table 1).

Obstetrics characteristics of the respondents

Among the respondents, 37 women (78.7%) from case group and 141 women (75%) from control group were multiparous, while 10 women (21.3%) from case group and 47 women (25%) from control group were multigravida. Among 235 women, 34 women (72.3%) from case group and 166 women (88.3%) from control group had planned their current pregnancy. Seventeen women (36.2%) from case group had a history of still birth while 38 women (20.2%) had a history of still birth from the control group. About 150 women (79.8%) from control group and 30 (63.8) from case group had no history of still birth (Table 2).

Sexually transmitted disease history related factors

Based on the results of this study, more than half of the women in the case group (30 (63.8%)) and 61 women (32.4) in the control group had a history of STI, whereas 17 women (36.2%) in the case group and 127 women (67.6%) in the control group did not have any history of STI. More than half of the women (25 (53.2%)) from the case group and 130 (69.1%) from control group had no history of hospital admission (Figure 2).

Lifestyle related factors

The study revealed that 16 (34%) pregnant women from case group and 34 (18.1%) from the control group consumed alcohol during pregnancy, while 31 (66%) from case group and 154 (81.9%) from the control group did not drink alcohol. More than two thirds of the women (32 (68.1%)) in the case group and one fourth from the control group (47 (25%)) had started sexual intercourse before 18 years of age. Regarding history of multiple sexual inter course, more than one third of the women (17 (36.2%)) from case group and majority (161 (85.6%)) from control group had no history of multiple sexual inter course (Table 3).

Bivariable binary logistic regression analysis of factors associated with syphilis infection

There were about 14 candidate variables in the bivariate analysis model with p-value <0.25. These were: educational status, previous history of multiple pregnancy, status of current pregnancy, ANC follow-up, history of abortion, still birth, history of STI, history of hospital admission, alcohol intake history, partner’s alcohol intake, using addictive substance, age at first sexual intercourse, multiple sexual partners, and maternal HIV co-infection were identified as candidate variables for multivariable logistic regression analysis. Then the above variables were entered into multivariable logistic regression for analysis (Table 4).

Multiple binary logistics regression analysis of factors associated with syphilis infection

After entering the variables with a p-value of <0.25 into multivariable analysis, the variables found to be significantly linked with syphilis infection were status of current pregnancy, ANC follow-up, history of STI, alcohol intake history, age at first sexual intercourse, and multiple sexual partners.

According to this study, the odds of syphilis infection were 2.697 times higher in pregnant women than women who did not plan their current pregnancy [AOR = 2.697, 95% CI (1.003-7.249)]. The odds of syphilis infection were 4.556 times more likely among pregnant women who had no ANC follow-up than pregnant women who had ANC follow-up [AOR = 4.556, 95% CI (1.759-11.80)]. The odds of syphilis infection were 3.080 times higher in pregnant women who had a history of STI [AOR = 3.080, 95% CI (1.347-7.043)].

Similarly, the odds of syphilis infection were 3.965 times higher among pregnant women who consumed alcohol than pregnant women who did not drink alcohol [AOR = 3.965, 95% CI (1.56-10.078)]. Likewise, pregnant women who had their first sexual intercourse before the age of 18 were 8.951 times more likely to have syphilis infection than women who had their first sexual intercourse after 18 years old [AOR = 8.951, 95% CI (3.70-21.646)]. In addition, the odds of syphilis infection were 2.754 times higher in pregnant women who had multiple sexual partners [AOR = 2.754, 95% CI (1.065-7.118)] (Table 5).

This study has attempted to analyze the determinants of syphilis infection among pregnant women attending ANC by incorporating as many risk factors as possible in order to reduce risks and complications related to syphilis infection.

The study identified that, status of current pregnancy, ANC follow-up, history of STI, alcohol intake history, age of first sexual intercourse, and multiple sexual partners were significantly associated determinant factors with syphilis infection among pregnant women attending ANC at public hospital of South West Shoa, Zone.

According to this study, pregnant women with a previous history of STI was more likely to have syphilis infection compared to those who had no previous history of STI. This study was comparable to the study conducted in hospitals of Wolaita zone, Southern Ethiopia which revealed that pregnant women who had STI were more likely to develop syphilis infection than those who had no STI [13]. This may be due to the fact that both STI and syphilis infection can be transmitted through unprotected sexual contact and women with current or past STI are at a greater risk for syphilis infection. Nonetheless, this study findings were not in line with a previous study conducted at Felege Hiwot Referral Hospital, Bahir Dar, northwest Ethiopia[ [11].

This study identified that; pregnant women who had no ANC follow up had higher odds of syphilis infection than those who had ANC follow up. It was supported by a study conducted in west Arsi zone, Ethiopia [20]. This could be due to the fact that women who had no ANC follow up may become pregnant either without planning or by unsafe sexual intercourse.

Additionally, the findings of this study showed that alcohol intake was the determinant of syphilis infection. Pregnant women who were intoxicated with alcohol were more likely to have syphilis infection than women who were not intoxicated with alcohol. This was similar to a previous study conducted at Jinka town public health facilities, Southern Ethiopia [17]. This may be due to the fact that alcohol consumption exposes the women for unsafe sexual practice.

Furthermore, this study also showed that women who had started their sexual intercourse before the age of 18 years were more likely to have syphilis infection than those who had started their sexual intercourse after the age of 18. This was supported by a study conducted at Dilla University Referral Hospital, Ethiopia [12]. This might be due to the societal norm of women marrying early or starting sexual activity at a young age, resulting in a higher risk of having many sexual partners and becoming more susceptible to syphilis infections.

The present study revealed that women with multiple sexual partners had higher odds to contract syphilis than women with no multiple sexual partners. This finding was similar with the study carried at Dilla University Referral Hospital, Ethiopia [12] and Jimma University Specialized Hospital, Ethiopia [10]. This might be due to the fact that the nature of the disease is asymptomatic in most of the cases and the partners might not seek treatment for the infections. Therefore, engaging in unprotected sex increases the chances of acquiring the diseases.

The findings of the current study showed that pregnant women who were unplanned with their current pregnancy had higher odds of contracting syphilis infection than women who had planned their current pregnancy. This might be as a result of women who had unplanned pregnancy may became pregnant by unsafe sexual intercourse which expose them to STIs like syphilis.

Syphilis infection is a significant public health concern that is linked with multiple factors. The findings of this study suggested that status of current pregnancy, ANC follow-up, history of STI, alcohol intake, age at first sexual intercourse, and multiple sexual partners were significantly associated determinants with syphilis infection among pregnant women attending ANC at Public hospital, South West Shoa. It is important to identify and address these factors in order to reduce new syphilis infections by preventing their impact. Health facilities (Hospitals) should strengthen routine laboratory testing of syphilis infection in all pregnant women attending ANC, as well as provide treatment to prevent new syphilis infections. Encourage screening and treatment of symptomatic and asymptomatic STIs in all pregnant women according to guidelines. Health care workers should provide community health education on risk factors of syphilis infections such as alcohol intake, age at first sexual intercourse started, and multiple sexual partners. Professionals who are working at antenatal care services should conduct routine investigation of syphilis infections and provide early treatment when necessary. Special attention should be given to the pregnant mother with a history of STI, alcohol intake, sexual intercourse started before 18 years old, and having multiple sexual partners. Pregnant mothers should avoid alcohol and having multiple sexual partners. Furthermore, they would need to prevent STI and seek prompt medical help if tested positive for any STI.

Magnitude of syphilis infection among pregnant women.

• Determinants of syphilis infection among pregnant women.
• The factors that led to pregnant women contracting syphilis.

There is no funding for this study.

Authors declare no conflict-of-interest with respect to this study.

The corresponding author is willing to provide the dataset that was used in this study based upon reasonable request.

All the authors contributed to the proposal development, questionnaires, data collecting process, analysis, and interpretation.

Data curation: Bacha Merga Chuko, Fikru Assefa Kibrat, Taka Girma, Zufela Sime Gari and Ararso Tafese

Format analysis: Bacha Merga Chuko, Fikru Assefa Kibrat, and Ararso Tafese ,Gada Edea and Shambel Negese Marami.

Investigation: Bacha Merga Chuko, Fikru Assefa Kibrat, Taka Girma, Zufela Sime Gari ,Ararso Tafese, Gada Edea and Shambel Negese Marami.

Methodology: Bacha Merga Chuko, Fikru Assefa Kibrat, Ararso Tafese, Gada Edea and Shambel Negese Marami.

Revising the manuscript. Bacha Merga Chuko, Fikru Assefa Kibrat, Taka Girma, Zufela Sime Gari and Shambel Negese Marami.

Final version of the article was checked by all authors.

Informed consent was taken from every study participant before the actual data collection started.

We would like to thank Ambo University, College of Health Science, Department of Public Health for funding and data collectors for their contribution to accomplishing this research.