Concurrent genital-anal human papillomavirus (HPV) infections may impose an increased anal cancer risk in women with HPV-related genital lesions. High viral load may facilitate genital-anal HPV concurrence. Genital and anal HPV is reduced by a bivalent HPV16/18 vaccine, yet the effect on concurrent genital-anal HPV remains unclear.

This study analyzed viral load in concurrent genital-anal HPV infections, relative to genital-only and anal-only HPV infections and the impact of vaccination in young women. We included 1074 women, who provided both genital and anal swabs. HPV detection and genotyping was performed using the SPF10-DEIA-LiPA25. HPV copy numbers were measured with type-specific qPCRs and corrected for cellular content to obtain the viral load.

Concurrent genital-anal HPV often had significantly higher genital viral load (0.09-371 c/cell) than genital-only HPV (3.17E-04-15.9 c/cell, p<0.0001 to p<0.05). Moreover, nearly all concurrent genital-anal HPV types had higher genital copy numbers per PCR reaction (157-416E04 c/rxn) than anal copy numbers (0.90-884E01 c/rxn, p<0.0001 to p<0.001). Vaccinated women had significantly less infections with HPV16/18 vaccine-types (2.8% vs 13.7%, p<0.0001) and HPV31/35/45 cross-protective types (7.4% vs 21.1%, p<0.0001) than unvaccinated women.

In conclusion, particularly high genital viral load is found in concurrent genital-anal HPV infections, which are effectively reduced by vaccination.