Objectives Hepatitis delta virus (HDV) is the smallest human virus that causes the most severe form of viral hepatitis. However, the virus’s biological features, transmission routes and causes of endemicity in particular populations are not yet fully understood. HDV shares the hepatitis B virus (HBV) parenteral mode of transmission with HBV; therefore, sexual transmissions are also possible. However, data on sexual transmission of HDV are limited.

Methods This study included 60 patients with chronic HBV/HDV coinfection. The median age (IQR) of patients was 35 (23–47) years, and all were Mongolian. HDV-RNA, HBV-DNA and hepatitis B surface antigens were tested in serum, seminal plasma and cervical swab samples collected at the Liver Centre, Mongolia. Binary logistic regression analysis was used to create a model that predicts the possibility of HDV detection in seminal plasma and cervical swab samples based on HDV-RNA levels in serum samples.

Results HDV-RNA was detected in cervical swab samples from 24 of 30 patients (80%) and in seminal plasma from 15 of 30 patients (50%) (Fisher’s exact test, p=0.03). Patients with detectable HDV-RNA in either seminal or cervical fluid samples showed higher levels of HDV-RNA in serum ((females: 6.44 vs 4.21 log IU/mL (p<0.0001); males: 6.69 vs 5.65 log IU/mL (p<0.0001)). A correlation between HDV-RNA levels in the serum was identified in females (r=0.56, p=0.004; 95% CI 0.206 to 0.788) but not in males (r=0.38, p=0.15, 95% CI −0.15 to 0.75). The regression model identified threshold points of serum HDV-RNA levels that can be used to predict HDV-RNA detection in seminal plasma and cervical swabs.

Conclusions HDV-RNA can be detected in cervical swabs and seminal plasma of patients with HBV/HDV coinfection, and the detection was more common in females than in males. The probability of HDV-RNA detection in male seminal plasma and female cervical swab samples can be predicted based on the HDV viral load in serum.