Increased Incidence of Chlamydia Due to Changes in Cancer Screening Guidelines

Recent cervical cancer screening guideline changes in Canada were associated with reduced chlamydia testing and reported new cases of chlamydia in women.

Extending recommended intervals for cervical cancer screening in Canada most likely contributed to a subsequent increase in the incidence of chlamydia reported in women, according to a population-based review published in the Annals of Family Medicine.1 

As tandem testing for cervical cancer and chlamydia is common in women, new guidelines released in Ontario, Canada in May of 2012 recommending less frequent Papanicolaou (Pap) smear screening for cervical cancer also reduced screening for chlamydia.2,3 “It is likely that because many doctors coupled STI (sexually transmitted infection) screening in women with Pap tests, and since Pap tests were done less frequently, testing of asymptomatic women for chlamydia was done less frequently, too,” study co-investigator Michelle Naimer, MD, MHSc, CCFP, clinical director of the Mount Sinai Academic Family Health Team in Toronto, Ontario, Canada, told Infectious Disease Adviser.

Updates to the Canadian guidelines for cervical cancer were released in alignment with modified recommendations from the United States Preventive Services Task Force (USPSTF) and the American Cancer Society that suggested screening every 3 years for cervical cancer in women older than 21, with no recommendation for screening in women younger than 21.4 The Canadian study found that younger women at high risk for chlamydia were disproportionately affected by this change, as the highest incidence of chlamydia was in individuals age 20 to 24.

The investigators from multiple clinical and public health institutions reviewed 1,357,840 chlamydia records from participants covered by the Ontario Health Insurance Plan (OHIP) and 738,743 people presenting to public health clinics who used Public Health Ontario’s laboratory (LabWare). They found that the frequency of chlamydia testing was reduced in all age groups, most significantly in young women age 15 to 19. Smaller differences were noted in the group age 20 to 24, while there was no effect in women older than 25.

At the same time, reported rates of chlamydia initially decreased in females younger than 25 in parallel with decreased chlamydia screening, while the rates in males of the same age remained constant. “There are different screening recommendations for men and women,” Dr Naimer pointed out. “We only used men in our study as a comparator to women, showing that in the same time frame, testing increased slightly for men, but decreased substantially in women.”

According to the investigators, this decrease actually represented a pool of approximately 2726 fewer cases detected annually in young women. The pattern then reversed and rates of chlamydia increased in 2014 and 2015 compared with historical rates, showing the impact of decreased screening.

The study results clearly pointed to a need for chlamydia and cervical cancer screening to be conducted at separate intervals appropriate for each; thus USPSTF released new guidelines for chlamydia.5 “Screening for chlamydia in sexually active women according to the CDC [Centers for Disease Control and Prevention] includes sexually active women under 25 years of age, sexually active women aged 25 years and older if at increased risk, and pregnant women. Frequency of testing depends on a person’s risk and should be discussed between doctor and patient,” Dr Naimer said, adding that, “Now that urine testing for chlamydia is available to screen patients who have no symptoms of chlamydia, there is an opportunity to make urine testing more available to people in high-risk groups.”

The study was limited by an inability to distinguish between diagnostic Pap testing and chlamydia testing on available records, and by the inclusion of women who may have required specialized cervical cancer screening. As it was conducted in only one Canadian province, the researchers cautioned that results were not generalizable to all of Canada. Finally, a true control group was not used for comparison.

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  1. Naimer MS, Kwong JC, Bhatia D, et al. The effect of changes in cervical cancer screening guidelines on chlamydia testingAnn Fam Med. 2017;15:329-334. doi:10.1370/afm.2097
  2. Cancer Care Ontario. Ontario cervical screening cytology guidelines summary. Toronto, ON: Ontario Cervical Cancer Screening Program, 2012. Revised October 2016. Accessed July 20, 2017.
  3. Dickinson J, Tsakonas E, Conner Gorber S, et al.; Canadian Task Force on Preventive Health Care. Recommendations on screening for cervical cancer. CMAJ. 2013;185:35-45. doi:10.1503/cmaj.121505
  4. US Preventive Services Task Force. Screening for cervical cancer: Topic page, 2012. Updated March 2012.  Accessed July 20, 2017.
  5. Tanksley A, Cifu AS. Screening for gonorrhea, chlamydia, and hepatitis B. JAMA. 2016;315:1278-1279. doi:10.1001/jama.2016.0223