10,758 women aged between 20 and 29 years of age with no history of abnormal cervical cell growth were given a cervical smear on joining the trial in 1991 and a follow up smear test two years later. Compared with women who were negative for human papillomavirus at enrolment, those who were HPV positive had a significantly increased risk at follow up of having squamous intraepithelial lesions; a precursor to invasive cervical cancer. Similarly, women who tested positive for HPV at the second examination had a strongly increased risk of low and high grade lesions.
However, women were most at risk of developing high grade lesions if they repeatedly tested positive to the same high risk HPV type.
The researchers conclude that HPV positivity precedes and predicts future cervical high grade lesions and that type specific persistence of HPV was strongly associated with the development of high grade lesions. In contrast for low grade lesions there was no significant difference in the risk associated with being HPV positive on both examinations with different types of HPV and having the same HPV type on both occasions.