Human papillomavirus types 16 and 18 DNA load in relation to coexistence of other types, particularly those in the same species

Abstract

Background: Infection with multiple human papillomavirus (HPV) types is common. However, it is unknown whether viral DNA load is related to the coexistence of other types.

Methods: Study subjects were 802 and 303 women who were positive for HPV16 and HPV18, respectively, at enrollment into the Atypical Squamous Cells of Undetermined Significance and Low-Grade Squamous Intraepithelial Lesion Triage Study. HPV16 and HPV18 E7 copies per nanogram of cellular DNA in cervical swab samples were measured by real-time PCR in triplicate.

Results: Concurrent coinfection was common in this population of women with minor cervical lesions; multiple HPV types were detected in 573 (71.4%) of 802 HPV16-positive women and 227 (74.9%) of 303 HPV18-positive women. The adjusted odds ratio associating coinfection with per 1 log unit increase in HPV16 DNA load was 0.78 (95% confidence interval, 0.68-0.89); it was 0.64 (95% confidence interval, 0.52-0.79) for a similar analysis of HPV18 DNA load. Women with, compared with without, coinfection of A9 species types possessed a significantly lower HPV16 DNA load (P < 0.001), whereas women with, compared with without, coinfection of A7 species types possessed a significantly lower HPV18 DNA load (P = 0.001). A trend of decrease in HPV16 DNA load with increasing number of the coexisting non-HPV16 A9 species types was statistically significant (P(trend) = 0.001).

Conclusion: Coinfection with other types was associated with lower HPV16 and HPV18 DNA load. The extent of reduction was correlated to phylogenetic distance of the coexisting types to HPV16 and HPV18, respectively.

Figure 1

Estimates of HPV16 copy number in 10 pair of samples with or without arbitrarily added A9 species types +. Samples 1-10, individually mixed with 10 samples containing HPV52, HPV31, HPV31/51, HPV52/62, HPV33/73, HPV35/51/52, HPV31/39/83, HPV18/53/67, HPV51/52/59/61, HPV33/39/51/52/59, respectably □. Samples 1-10, individually mixed with HPV-negative samples * Difference = log₁₀ units (of sample with A9 types) minus log₁₀ units (of sample with HPV-negative sample)