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When, a handful of years ago, the U.S. and Canada changed their screening guidelines for cervical cancer, it was an acknowledgment that screenings for young women carried unintended harms.

However, a new study shows they also carried unintended benefits. As Pap screenings for women under 24 became less frequent in Ontario in 2012-2014, fewer cases of the bacterial infection chlamydia were caught — putting women at risk of potentially serious consequences.


The finding represents the challenge public health officials face in striking a balance between harms and benefits of disease screenings — some of which extend far beyond the condition actually being tested for.

Chlamydia is the most common sexually transmitted infection in the U.S. and worldwide, with over 1.5 million cases reported to the Centers for Disease Control and Prevention in 2015. It can easily be cleared up with antibiotics, but often doesn’t have symptoms. Men with chlamydia rarely have health problems, but women who aren’t treated can develop pelvic inflammatory disease, which damages their reproductive system and can cause infertility.

The CDC recommends that sexually active women under 25 get tested for chlamydia every year. Prior to 2012, this was generally done with a swab test during a woman’s annual Pap screening.


But Pap guidelines in the U.S. and Canada changed in 2012, putting a lower age limit on the test for the first time. The new guidelines in both countries recommend against Pap screenings for women under 21, after research indicated that cervical cancer was extremely rare and slow-growing in young women. The guidelines also reduced the frequency of screenings for women 21 and up to once every three years.

But, as a result, chlamydia screening “just kind of dropped off the radar” of clinicians, said Dr. Margaret Long, an OB-GYN at Mayo Clinic.

To quantify that impact, researchers used two databases of health information of Ontario residents: one that determined the total number of chlamydia tests based on billing information, and another that recorded the total number chlamydia cases as reported to the province’s public health department.

The researchers found that between 2012 and 2014, chlamydia screening dropped 26 percent for women between 15 and 19, and 18 percent for 20-to-24-year-old women. Meanwhile, cases of the infection decreased by 17 percent in the younger group and 14 percent in the older group — which was not necessarily a good thing.

“It’s not that the actual incidence has gone down, it’s just you’re not identifying them,” said Dr. Michelle Naimer, a family physician at Mount Sinai Hospital and an associate professor at the University of Toronto who co-led the study published Monday in Annals of Family Medicine. “And then the risk of that is that down the road, it will just spread more and you will have more cases in the future.”

Naimer said unpublished data from their group indeed show more cases in 2015 and 2016. But without data on screening numbers, she cautioned, it’s unclear whether that points to more thorough screening or a real rise in disease spread.

Fortunately, there may be a simple fix: Urine testing for chlamydia has become much more reliable in recent years. These days a urine test is as sensitive and specific as swab testing, and doesn’t require a pelvic exam.

Still, whether clinicians remember to administer this new type of test is a different question. Naimer thinks including reminders in electronic medical systems could help, as could leaving urine collection containers out in waiting rooms so patients can decide for themselves whether or not they want or need a chlamydia screening.

“I think there just needs to be education: public education and education of primary care providers to do things a little bit differently than we’ve done in the past in light of these new guidelines,” she said.

Long’s advice for young women who are sexually active is simple: “If your doctor wants to do a chlamydia screening, just say yes. Don’t think about it a lot, just do it.”