***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Purpose Acquisition of human papillomavirus ( HPV ) in women occurs predominantly through vaginal sex . However , HPV has been detected in girls reporting no previous sex . We aim ed to determine incidence and risk factors for HPV acquisition in girls who report no previous sex in Tanzania , a country with high HPV prevalence and cervical cancer incidence . Methods We followed 503 adolescent girls aged 15–16 years in Mwanza , Tanzania , with face-to-face interviews and self-administered vaginal swabs every 3 months for 18 months ; 397 girls reported no sex before enrollment or during follow-up ; of whom , 120 were r and omly selected . Sample s from enrollment , 6- , 12- , and 18-month visits were tested for 37 HPV genotypes . Incidence , clearance , point prevalence , and duration of any HPV and genotype-specific infections were calculated and associated factors were evaluated . Results Of 120 girls who reported no previous sex , 119 were included , contributing 438 sample s. HPV was detected in 51 ( 11.6 % ) sample s. The overall incidence of new HPV infections was 29.4/100 person-years ( 95 % confidence interval : 15.9–54.2 ) . The point prevalence of vaccine types HPV-6,-11,-16 , and -18 was .9 % , .9 % , 2.0 % , and 0 % , respectively . Spending a night away from home and using the Internet were associated with incident HPV , and reporting having seen a pornographic movie was inversely associated with HPV incidence . Conclusions Incident HPV infections were detected frequently in adolescent girls who reported no previous sex over 18 months . This is likely to reflect under-reporting of sex . A low-point prevalence of HPV genotypes in licensed vaccines was seen , indicating that vaccination of these girls might still be effective UNLABELLED In Rakai , Ug and a , human immunodeficiency virus (HIV)-positive men were r and omized to undergo either immediate circumcision ( intervention arm ) or delayed circumcision ( control arm ) . Penile swab sample s were assayed for high-risk human papillomavirus ( HR-HPV ) by Roche HPV Linear Array at enrollment and at 24 months ( intervention arm , 103 subjects ; control arm , 107 subjects ) . Rate ratios ( RRs ) of HR-HPV were estimated by Poisson regression . At 24 months , HR-HPV prevalence was found in 57 ( 55.3 % ) of 103 subjects in the intervention arm and in 77 ( 71.7 % ) of 107 subjects in the control arm ( RR , 0.77 ; 95 % confidence interval [ CI ] , 0.62 - 0.97 ) . Multiple HR-HPV infections were found in 19 ( 22.4 % ) of 85 subjects in the intervention arm and in 45 ( 42.5 % ) of 106 subjects in the control arm ( RR , 0.53 ; 95 % CI , 0.33 - 0.83 ) . New HR-HPV genotypes were acquired by 34 ( 42.0 % ) of 81 subjects in the intervention arm and by 53 ( 57.0 % ) 85 subjects in the control arm ( RR , 0.74 ; 95 % CI , 0.54 - 1.01 ; P = .06 ) . Multiple new HR-HPV genotypes were acquired by 8 ( 9.9 % ) of 81 subjects in the intervention arm and by 23 ( 24.7 % ) of 93 subjects in the control arm ( RR , 0.40 ; 95 % CI , 0.19 - 0.84 ; P = .01 ) . Circumcision did not affect the acquisition of single HR-HPV infections ( RR , 1.00 ; 95 % CI 0.65 - 1.53 ) or clearance of HR-HPV infections ( RR , 1.09 ; 95 % CI 0.94 - 1.27 ) . Circumcision of HIV-positive men reduced the prevalence and incidence of multiple HR-HPV infections . TRIAL REGISTRATION Clinical Trials.gov identifier : NCT00124878 Background More information is needed about time between sexual initiation and human papillomavirus ( HPV ) infection and development of cervical precancer . Methods The objectives were to investigate the time between first sexual activity and detection of first cervical HPV infection or development of first cervical intraepithelial neoplasia ( CIN ) , and associated factors in women from the double-blind , multinational , 4-year PATRICIA trial . PATRICIA enroled women aged 15 - 25 years with no more than 6 lifetime sexual partners . Women were r and omized 1:1 to the HPV-16/18 AS04-adjuvanted vaccine or to control , but only women from the control arm who began sexual intercourse during the study or within 6 months before enrolment , and had no HPV infection detected before the recorded date of their first sexual intercourse , were included in the present analysis . The time between onset of sexual activity and detection of the first cervical HPV infection or development of the first CIN lesion was analyzed using Kaplan-Meier and univariate and multivariable Cox proportional-hazards models . Results A total of 9337 women were enroled in the control arm of PATRICIA of whom 982 fulfilled the required inclusion criteria for analysis . A cumulative total of 28 % , 44 % , and 62 % of the subjects had HPV infection within 12 , 24 , and 48 months , respectively . The overall incidence rate was 27.08 per 100 person-years . The most common oncogenic types associated with 6-month persistent infection were HPV-16 ( incidence rate : 2.74 per 100 person-years ) , HPV-51 ( 2.70 ) , HPV-52 ( 1.66 ) , HPV-66 ( 1.14 ) , and HPV-18 ( 1.09 ) . Increased infection risk was associated with more lifetime sexual partners , being single , Chlamydia trachomatis history , and duration of hormone use . CIN1 + and CIN2 + lesions were most commonly associated with HPV-16 , with an overall incidence rate of 1.87 and 1.07 per 100 person-years , respectively . Previous cervical HPV infection was most strongly associated with CIN development . Conclusions More than 25 % of women were infected with HPV within 1 year of beginning sexual activity . Without underestimating the value of vaccination at older ages , our findings emphasize its importance before sexual initiation . Trial registration clinical trials.gov : NCT00122681 Background While infections with human papillomavirus ( HPV ) are highly prevalent among sexually active young women in Ug and a , information on incidence , clearance and their associated risk factors is sparse . To estimate the incidence , prevalence and determinants of HPV infections , we conducted a prospect i ve follow-up study among 1,275 women aged 12 - 24 years at the time of recruitment . Women answered a question naire and underwent a pelvic examination at each visit to collect exfoliated cervical cells . The presence of 42 HPV types was evaluated in exfoliated cervical cells by a polymerase chain based ( PCR ) assay ( SPF10-DEIA LiPA ) . Results Three hundred and eighty ( 380 ) of 1,275 ( 29.8 % ) women were followed up for a median time of 18.5 months ( inter-quartile range 9.7 - 26.6 ) . Sixty-nine ( 69 ) women had incident HPV infections during 226 person-years of follow-up reflecting an incidence rate of 30.5 per 100 person-years . Incident HPV infections were marginally associated with HIV positivity ( RR = 2.8 , 95 % CI : 0.9 - 8.3 ) . Clearance for HPV type-specific infections was frequent ranging between 42.3 % and 100.0 % for high- and 50 % and 100 % for low-risk types . Only 31.2 % of women cleared all their infections . Clearance was associated with HIV negativity ( Adjusted clearance = 0.2 , 95 % CI : 0.1 - 0.7 ) but not with age at study entry , lifetime number of sexual partners and multiplicity of infections . The prevalence of low- grade squamous intraepithelial lesions ( LSILs ) was 53/365 ( 14.5 % ) . None of the women had a high- grade cervical lesion ( HSIL ) or cancer . Twenty-two ( 22 ) of 150 ( 14.7 % ) HPV negative women at baseline developed incident LSIL during follow-up . The risk for LSIL appeared to be elevated among women with HPV 18-related types compared to women not infected with those types ( RR = 3.5 , 95 % CI : 1.0 - 11.8 ) . Conclusions Incident HPV infections and type-specific HPV clearance were frequent among our study population of young women . These results underscore the need to vaccinate pre-adolescent girls before initiation of sexual activity BACKGROUND Primary analyses of a study in young women aged 16 - 26 years showed efficacy of the nine-valent human papillomavirus ( 9vHPV ; HPV 6 , 11 , 16 , 18 , 31 , 33 , 45 , 52 , and 58 ) vaccine against infections and disease related to HPV 31 , 33 , 45 , 52 , and 58 , and non-inferior HPV 6 , 11 , 16 , and 18 antibody responses when compared with quadrivalent HPV ( qHPV ; HPV 6 , 11 , 16 , and 18 ) vaccine . We aim ed to report efficacy of the 9vHPV vaccine for up to 6 years following first administration and antibody responses over 5 years . METHODS We undertook this r and omised , double-blind , efficacy , immunogenicity , and safety study of the 9vHPV vaccine study at 105 study sites in 18 countries . Women aged 16 - 26 years old who were healthy , with no history of abnormal cervical cytology , no previous abnormal cervical biopsy results , and no more than four lifetime sexual partners were r and omly assigned ( 1:1 ) by central r and omisation and block sizes of 2 and 2 to receive three intramuscular injections over 6 months of 9vHPV or qHPV ( control ) vaccine . All participants , study investigators , and study site personnel , laboratory staff , members of the sponsor 's study team , and members of the adjudication pathology panel were masked to vaccination groups . The primary outcomes were incidence of high- grade cervical disease ( cervical intraepithelial neoplasia grade 2 or 3 , adenocarcinoma in situ , invasive cervical carcinoma ) , vulvar disease ( vulvar intraepithelial neoplasia grade 2/3 , vulvar cancer ) , and vaginal disease ( vaginal intraepithelial neoplasia grade 2/3 , vaginal cancer ) related to HPV 31 , 33 , 45 , 52 , and 58 and non-inferiority ( excluding a decrease of 1·5 times ) of anti-HPV 6 , 11 , 16 , and 18 geometric mean titres ( GMT ) . Tissue sample s were adjudicated for histopathology diagnosis and tested for HPV DNA . Serum antibody responses were assessed by competitive Luminex immunoassay . The primary evaluation of efficacy was a superiority analysis in the per- protocol efficacy population , supportive efficacy was analysed in the modified intention-to-treat population , and the primary evaluation of immunogenicity was a non-inferiority analysis . The trial is registered with Clinical Trials.gov , number NCT00543543 . FINDINGS Between Sept 26 , 2007 , and Dec 18 , 2009 , we recruited and r and omly assigned 14 215 participants to receive 9vHPV ( n=7106 ) or qHPV ( n=7109 ) vaccine . In the per- protocol population , the incidence of high- grade cervical , vulvar and vaginal disease related to HPV 31 , 33 , 45 , 52 , and 58 was 0·5 cases per 10 000 person-years in the 9vHPV and 19·0 cases per 10 000 person-years in the qHPV groups , representing 97·4 % efficacy ( 95 % CI 85·0 - 99·9 ) . HPV 6 , 11 , 16 , and 18 GMTs were non-inferior in the 9vHPV versus qHPV group from month 1 to 3 
    Output:
    
In published studies different epidemiological assumptions are used to estimate IRs of grouped HPV types , leading to widely differing estimates of IRs .