The Science of Sex: Chlamydia

Pin it

Does Chlamydia Cause Cancer? index

In recent years, the bacterium Chlamydia trachomatis has grabbed the number two spot in the rogues’ gallery of STD-causing organisms, right behind human papillomavirus or HPV (the cause of genital warts and cervical dysplasia). Now a Scandinavian research group has identified a new long-term complication of chlamydial infection — a heightened risk of cervical cancer.


It’s a scary prospect for sexually active women, who are already juggling the complexities of negotiating safe sex.


Chlamydia is responsible for about three million new infections in the U.S. annually. The symptoms of an infection are usually mild, such as a thin discharge from the vagina or penis and discomfort on urination. Oftentimes, symptoms are absent altogether. Still, the consequences of untreated chlamydial infections can be severe, especially in women: pelvic inflammatory disease, infertility and ectopic pregnancy.


Cervical cancer is the scariest prospect yet. It’s been known for some years that HPV is the leading cause of the disease, but since the mid-1980s, there have been hints that chlamydia might also play a role: several studies have found that women with cervical cancer have an increased likelihood of possessing antibodies to chlamydia, meaning that they were exposed to the bacterium at some time in the past.


In an attempt to string apart this complicated data, Finnish, Swedish and Norwegian researchers got together to run a “longitudinal” study — one that studies patients at more than one point in time. Scandinavia is a happy hunting ground for this sort of project, because of the stability of the population and the near-obsessive collection of patient information by centralized health services. In addition, serum samples have already been collected from a large fraction of the population: one serum bank, for example, contains samples from virtually every Finnish women who has ever been pregnant over the last twenty years. Nothing remotely like this exists in the U.S.


The researchers (led by Jorma Paavonen of the University of Helsinki) identified a population of half a million women who had received serum samples some years previously. They then checked data banks to find women from this population who later developed cervical cancer, identifying 181 such women. Then they tested the earlier serum samples from these women for chlamydia, along with samples from 533 matched “control” women who did not have cervical cancer.


The results, published this month in the Journal of the American Medical Association (JAMA), indicated that exposure to chlamydia is indeed associated with an increased risk of later developing invasive cervical cancer. What’s more, the researchers found that the risk was greatest with certain strains of chlamydia — especially one called “strain G.” (This finding echoes an independent Finnish study, published four years ago.) Although researchers don’t know yet what’s so dangerous about strain G, the finding strengthens the notion that chlamydia infection causes cervical cancer, rather than just being correlated with it.


The study’s findings have both scientific and practical significance. At a scientific level, they raise obvious questions about how chlamydia has its cancer-promoting effect. Does it act as some kind of sidekick to the main villain, HPV, or does it work independently? Does chlamydia need to be present for a long period of time — perhaps causing chronic inflammation — or is a single brief infection all that is necessary? These will be avenues for future research. And because the entire genome of Chlamydia trachomatis was recently sequenced, it may be possible to identify genes responsible for the organism’s carcinogenic action.


Cervical cancer is not on the rise, so there’s no reason to think that chlamydia will cause an explosion of cancer in the future. But there is every reason to expand screening programs: infections can be diagnosed from urine samples and treated effectively with antibiotics, thus preventing long-term complications.


Chlamydia is a young woman’s disease. Most women with the disease are under thirty, and a large fraction are teenagers. A trial screening at three Louisiana high schools, whose results were published last year, found that six percent of the boys and thirteen percent of the girls were currently infected. (The difference between the sexes reflects the fact that chlamydia is transmitted more easily from male to female than vice versa.) Yet school screening programs for sexually transmitted diseases are notoriously difficult to organize. Compounding the problem, HMOs have widely diverging policies regarding chlamydia screening. According to a recent RAND report, some HMOs screen as few as two percent of the young, sexually active women who visit their clinics.


Unfortunately, the new administration is unlikely to make safe sex and good STD treatment a priority — preferring to let a thousand abstinence-based programs bloom. For the rest of us, the message of this new study may be dull, but it’s even more crucial: condoms, condoms, condoms; get tested; and get politically active, so that treatment and educational programs go to the kids who need them.