TORONTO -- Young women in Ontario are being screened for sexually transmitted infections far less often since updated guidelines reduced the frequency of Pap tests for cervical cancer, a study suggests.

Researchers at St. Michael's Hospital in Toronto found the guidelines, which were rewritten in 2012, reduced Pap smear rates by 60 per cent in the year after their introduction -- and that led to a 50 per cent drop in gonorrhea and chlamydia testing among women aged 15 to 24. Patients were also less likely to be screened for syphilis, hepatitis C and HIV.

Prior to 2012, women were advised to start cervical cancer screening within three years of becoming sexually active, followed by annual testing. After three normal Pap test results, subsequent screening was recommended every two or three years until age 70.

The updated guidelines by Cancer Care Ontario recommend starting Pap tests at age 21 for women who have been sexually active, with three-year screening intervals if test results are normal.

The advice differs slightly from guidelines by the Canadian Task Force on Preventive Health Care, which recommends that routine Pap tests for women start at age 25 and continue every three years until age 70, when they can cease if a woman has had three successive negative tests in the previous 10 years.

"Historically, we know that Pap tests and STI screening are linked because they're often performed at the same time," said lead author Dr. Tali Bogler, a family physician at St. Mike's.

But because women aren't visiting their doctors as often for Pap smears, that's caused a drop in screening for STIs, she said Thursday, noting that chlamydia and gonorrhea are common among young women and incidence of those infections is on the rise.

In the last decade, chlamydia rates have jumped 72 per cent, while gonorrhea rates have gone up by more than 50 per cent.

The study, published Thursday in the journal Canadian Family Physician, tracked patient charts across five primary care sites at St. Michael's Hospital in the year before the guidelines changed and in the year after.

Researchers found rates of Pap smear testing among women in the study dropped from 42 per cent before the guideline change to 17 per cent after, and screening of gonorrhea and chlamydia decreased from 40 per cent to 20 per cent.

"Our findings suggest a possibly harmful public health consequence," said Bogler.

"So I think a big piece of this is really educating the public, and especially young women, to understand that even though they haven't had a Pap test, they need to be screened for STIs if they're at risk."

Often, women can be infected with an STI like chlamydia or gonorrhea and have no symptoms. But left untreated, the infection can last a long time and cause pelvic inflammatory disease, which can lead to chronic pelvic pain, infertility or an ectopic pregnancy in women who do conceive.

"Therefore it's critical that family physicians find new and innovative ways to screen for STIs in sexually active women under 25," she said, suggesting that doctors might not think about asking a patient about their sexual health or STI risk during visits unrelated to Pap testing.

"Physicians should think about that when they're coming in for a cough or cold or other things that (provide) other opportunities to screen for STIs."

While such testing is often done with a vaginal swab during the procedure to screen for cervical cancer, self-administered urine-based testing can also pick up sexually transmitted infections "and can be easily extended into community settings," she said.

Bogler said this non-invasive testing method could be used in high schools, universities and other community outreach sites to help young women access treatment and avoid the long-term health complications of an untreated STI.