Human papillomavirus type 16 and 18 viral clearance and progression to precancer among women aged 18-25 years enrolled in the Costa Rica HPV prophylactic vaccine trial (CVT).
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BACKGROUND: New approaches to control HPV infections and prevent progression to cervical precancer are needed. We investigate the probability of viral clearance and progression to cervical precancer in women infected with HPV16/18 without evidence of precancer at study enrollment to inform research efforts targeted at reducing cervical cancer. METHODS: We included 530 women aged 18-25 who tested HPV16/18 DNA-positive and did not have cytological evidence of high-grade-squamous-intraepithelial-lesion (HSIL) at enrollment in CVT. At each visit, clinicians collected cervical cells for cytology and HPV-DNA testing. Those with abnormal cytology were referred to colposcopy, biopsy, and treatment as needed. We estimated the probability of HPV clearance (loss of detection) and progression to intraepithelial neoplasia grades 2 or 3 or worse (CIN2+, CIN3+) based on histological findings by expert pathologists over 4-years of follow-up. RESULTS: At enrollment, there were 550 prevalently detected HPV16 and/or HPV18 infections among 530 women without cytologic HSIL. Corresponding probabilities of HPV16 and HPV18 clearance were 68.5 % (95 %CI 63.6 %-73.0 %) and 85.0 % (78.6 %-90.1 %) by 24-months and 82.1 % (78.0 %-85.7 %) and 90.2 % (84.7 %-94.2 %) by 48-months after initial detection. Risk of clearance of prevalently detected HPV16 and HPV18 infections decreased with increasing age by 12-, 24-, 36-, and 48-months after initial detection (ptrend-values≥0.31). Among the same 530 women, by 24-months and 48-months of follow-up, the corresponding probabilities of progression to CIN2+ were 5.5 % (3.8 %-7.7 %) and 13.0 % (10.4 %-16.1 %), and to CIN3+ were 2.6 % (1.5 %-4.3 %) 7.5 % (5.5 %-10.0 %). Probability of progression was 2-5 times higher in women with HPV16 infections than with HPV18. Risk of progression to CIN2+ and CIN3+ increased with increasing age during the follow-up period (ptrend-values≥0.11). CONCLUSIONS: Among young adult women without evidence of HSIL by cytology, clearance of prevalently detected HPV16/18 infection is a common event, and progression to precancer occurs infrequently but in a sizeable proportion of those with prevalent infection.