The POPI trial had recruited young women (under 28 years) attending universities check details and further education colleges in London between 2004 and 2006 to a study of the impact of chlamydia screening on pelvic inflammatory disease [11]. Women who had never had sexual intercourse, had been tested for chlamydia in the previous three months or were pregnant were excluded. Archived

(at −80 °C) first (trial entry) samples from women aged under 25 years were sent to the HPA for HPV testing. For each sample, age, year of birth, ethnicity, date of sample collection, chlamydia test result, and number of sexual partners in the previous 12 months were obtained from the POPI database. NCSP samples were received and processed at HPA in a median (inter-quartile range (IQR)) of 5 (3–7) weeks from collection. POPI samples were retrieved from archive and defrosted at 4 °C. Two aliquots of 300 μL each were centrifuged (13,000 × g, 5 min) and the cellular pellets stored at −25 °C prior to testing (one pellet was resuspended in 300 μL phosphate buffered saline (PBS) before storage).

The samples were screened for the presence of HPV using the Hybrid Capture 2 HPV DNA test (hc2; originally developed by the Digene selleck chemicals llc Corporation, and now marketed by Qiagen). The Combined-Probe Cocktail Method was used to detect high-risk (HR; HPV 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59 and 68) and low-risk (LR; HPV 6, 11, 42, 43 and 44) HPV types. The hc2 test was conducted according to the manufacturer’s instructions with some modifications necessitated by the use of VVS samples. Briefly, the cellular

pellet was resuspended in 75 μL Specimen Transport Medium with Denaturation Reagent. Cells were then inhibitors denatured under alkaline conditions and hybridized with a pool of HR and LR RNA probes. The resulting HPV DNA:RNA hybrids were captured onto microtiter plates with antibodies specific for DNA:RNA hybrids and detected using alkaline phosphatase-conjugated anti-DNA:RNA antibody in conjunction with a chemiluminescent substrate. If the signal output, in relative light units (RLU), was above the test cutoff (CO) the sample was considered to contain HPV DNA (i.e. RLU/CO > 1). Hc2 positive samples were genotyped using Calpain the Linear Array HPV Genotyping test (LA; Roche Molecular Systems). DNA was extracted from 300 μL of the PBS-resuspended cellular pellet using the automated BioRobot Universal platform (Qiagen, UK) using the QIAamp® DNA Blood BioRobot® MDx kit and the extraction protocol QIAamp ‘One for All UNIV rcV23’. Extracted DNA (50 μL of 100 μL total eluate) was then amplified using the PGMY primer reagents provided in the LA kit. LA can detect 37 HPV types (HPV 6, 11, 16, 18, 26, 31, 33, 35, 39, 40, 42, 45, 51, 52, 53, 54, 55, 56, 58, 59, 61, 62, 64, 66, 67, 68, 69, 70, 71, 72, 73 (MM9), 81, 82 (MM4), 83 (MM7), 84 (MM8), IS39, and CP6108) and includes a beta-globin probe to check for sample integrity.