S1 Data -

Background
The burden of parallel and overlapping infections of Sexually Transmitted Infections (STIs), particularly HIV, syphilis, hepatitis B (HBV), and hepatitis C virus (HCV) are disproportionately higher among pregnant women globally, leading to unwanted consequences. These infections pose significant public health challenges as they can be transmitted vertically to the offspring. This study aimed to determine the sero-epidemiological patterns and predictors of STIs (HIV, syphilis, HBV, and HCV) among pregnant women attending antenatal care clinics at ten health facilities in North-eastern Ethiopia.
Methods
An institution-based multi-center cross-sectional study was conducted from May to November 2022 among 422 pregnant women selected using simple random sampling technique. Semi-structured questionnaire was used to collect socio-demographic characteristics and predictor variables of STIs through face-to-face interviews. Venous blood was collected and it was tested for anti-HIV, HBsAg, anti-HCV, and anti-Treponemal antibodies using immunochromatographic test kits. Multinomial logistic regression analysis was used to identify associated factors of STIs. Variables with an adjusted odds ratio (AOR) and a p-value <0.05 were considered statistically significant.
Results
The overall prevalence of STIs was 23.9% (95% CI = 20.08–28.25). The prevalence of parallel infections of HIV, hepatitis B, hepatitis C, and syphilis were 6.4%, 9%, 1.7%, and 6.9%, respectively. The overlapping infections for HIV-HBV was 4% but HIV-HCV overlapping infection wasn’t found. Increased age, tattooing, multiple sexual partners, exposure to unsafe sex, and RH status were independent factors of HBV. Likewise, increased age, rural residence, illiteracy, and tattooing were independently associated with HCV. Moreover, rural residence and a history of tattooing were independent predictors for the acquisition of HIV, whereas multiple sexual partners and RH status were found to be significant predictors of syphilis infection among pregnant women.
Conclusion
The magnitude of overlapping and parallel STD infections is still continued to be a problem among pregnant women. Moreover, there were overlapping infections of HBV-HIV. Therefore, continuous screening of pregnant women for HIV, syphilis, hepatitis B, and C infections should be performed, and special attention should be given to pregnant women who have co-infections.