HPV-16 infection and cervical cancer: modeling the influence of duration of infection and precancerous lesions.

The patterns of transmission, clearance, and progression of HPV infection and the related precancerous lesions are key to accurately model cervical cancer epidemiology and prevention. We have developed an age-structured dynamic model of the transmission of HPV-16 infection. This mathematical model accounts, for the first time, for the effect of infection and precancerous lesions duration on the natural history of HPV-16 infection and precancerous lesions. The model's output has been fitted to contemporaneous sets of data from Turin, Italy, to estimate parameters that have had been indirectly tested by comparing them with other estimates reported in the literature. The average probability of HPV-16 infection transmission per sexual partnership was about 40%. The HPV-16 clearance and progression rates decreased as the length of time with infection increased, clearance ranging between 1.6 per woman-year (in the first 6 months of infection) and 0.036 (after more than 6 years of infection), and progression between 0.072 and 0.018 per woman-year. The rate of clearance of precancerous lesions (CIN2+) was inversely dependent on age, while the progression of CIN2+ toward invasive cervical cancer increased as the precancerous lesions persisted. The present study also suggests that an exclusive role of women's age in shaping the rate of progression to cancer is unlikely. These results should inform future analyses. Including more accurately the role of the duration of infection and precancerous lesions as determinants of the cervical cancer occurrence in models of cervical cancer control may influence predictors of the effectiveness of intervention strategies.