Multiple human papilloma virus types in cervical infections: competition or synergy?

Coinfection with multiple human papilloma virus (HPV) types is common in cervical HPV infection. To evaluate if infections with different HPV types occur independently, we examined 3558 women above 15 years of age suspected of cervical HPV infection. Among them, 1842 (52%) women were HPV negative and 1716 (48%) were HPV positive as analysed by a PCR-based commercial microarray assay for mucosal types. Of the HPV-positive samples, 824 (48%) had single infections, while 892 (52%) had multiple infections. Observed numbers of concurrent HPV types differed from expected numbers under the assumption of independence between infections by the various HPV types. Significant positive associations were observed for 16 pairs of HPV types in statistical analysis accounting for mass significance. Significant negative associations were also found, i.e. women with HPV-16 infection had 0.4 times the odds of having HPV-51 compared with women not infected with HPV-16. HPV-16 was the only type with odds ratios <1 for all pairwise combinations. While our findings of statistically significant coexistence do not prove biological dependence among HPV types, they do suggest that infections with some HPV types may depend on the existence of certain other HPV types. Any interaction between coexisting HPV types could either decrease or increase the efficacy of current HPV vaccines that offer mainly type-specific protection, depending on whether the types vaccinated against compete with other HPV types or not.