A study by doctors at Limerick’s sexually transmitted disease (STD) clinic suggests further evidence of a link between underage sex and cervical cancer.

An audit of smear tests and follow-up examinations found 37% of those with high-grade pre-cancerous lesions of the cervix were under 25 years of age. Of these, 62% first had sex before they were 14.

The study, published in the journal BMC Research Notes, said the younger onset of sexual activity “may contribute to the earlier age of onset of this cancer”.

High-grade lesions — classified as cervical intraepithelial neoplasia (CIN3) — are abnormal tissue which, if left untreated, can progress to invasive cancer.

Of the under-25s with these lesions, 43% had human papilloma virus (HPV), also called genital warts, which has long been associated with cervical cancer, and 13% had chlamydia, another possible cause of the disease. These women had an average of 5.5 sexual partners in their lives.

Catherine O’Connor, director of the STD clinic, said: “Chlamydia is mainly a young person’s infection and has been implicated in causing changes in smears. I was surprised with the number under 25 that had CIN3 and chlamydia — 80%.

“Half had HPV, which is what one might expect, as it is well recognised as a cause of these changes and is a common condition. So many people have it, I call it ‘Ireland’s best kept secret’ as no one talks about it.”

In 2006 there were 9,892 sexually transmitted infections (STIs) notified in Ireland. This was almost treble the rate in 1995.

The highest number of cases was among those aged 20-29 years, who accounted for 65% of all STI notifications. The number of cases of chlamydia rose from 245 in 1995 to 3,144 in 2006, while genital warts have gone from 1,972 to 3,494 cases a year.

In its 2006 report the Health Protection Surveillance Centre said the data “suggests considerable risk-taking behaviour in the form of unprotected intercourse”.

The Limerick study analysed 2,637 smear test results, 221 of which were referred for colposcopy, a medical procedure to examine the cervix which can involve a biopsy. “We are dealing with an ‘at risk’ group and it should be added to the other ‘at risk’ groups [for screening],” said O’Connor.

The incidence of cervical cancer in Ireland rose by 36% between 1994 and 2000 and is increasing at a rate of 1.5% annually. Every year 77 women die in Ireland from the disease.

A national cervical cancer screening programme has been promised. A pilot scheme has been running in Limerick since 2000 and is due to be launched nationally later this year. Under-25s will not be included.

“The recommendations set out by the pilot group were not to screen those under the age of 25,” said Mortimer O’Connor, another doctor involved in the study. “We carried out this audit to see was it justifiable for us to stop or continue. The results back up that it may be beneficial if we continue the opportunistic screening. It is showing there is a population at risk under 25.”

Last month Tony O’Brien of the National Cancer Screening Service said the screening programme will be ready to be launched in the coming months.

The service will be free to all women in Ireland aged between 25 and 60.

Screening will be provided every three years for women aged between 25 and 44 and every five years for women aged between 45 and 60.

Quest Diagnostics, an American laboratory, has been awarded a two-year contract to analyse 300,000 smears as part of the free screening.

A report from the Health Information and Quality Authority last month recommended that a vaccine to guard against the most common strains of HPV be given to all 12-year-olds. It needs to be administered before the person becomes sexually active.

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