Chlamydia false positive?

[eurydice3000]

I am a 28 y/o female. my partner and I have unprotected oral, vaginal and anal sex.  After a 1 year together, I tested negatively for all common STDs, including Chlamydia.  the last 12 months (after my last testing) we have been experimenting with an "open" sexual relationship.  we have each had other sexual partners with whom we practiced unprotected oral and protected vaginal sex.

2 weeks ago my partner had a sexual encounter with a woman who has had no previous sexual partners.  They had unprotected oral sex, protected vaginal sex and unprotected anal sex.  4 days later she felt feverish and had urinary discomfort and went to the doctor.  She was tested for several STDs and was diagnosed with a UTI.  She tested positive for chlamydia (from a culture) and for some other bacterial infection that she could not remember the name of when she spoke with my partner.

he and I were immediately tested and my partner, after samples were taken for testing,  was treated for chlamydia (with zithromax)

Both my partner and I tested negatively for chlamydia (as well as HIV, Ghonneria, etc).  To be extra sure, my partner had a urine test and a swab test taken for his tests.

1.  Is it possible that this woman had a false positive test for chlamydia?

2. Is it likely that my partner and I both have chlamydia but tested negately (once for me, twice for him)?

3. I had been sick (head cold) when I performed oral sex on my partner the day before he had intercourse with this other woman.  I had a friend who got quite ill and was told she had an STI which later turned out, as it was explained to her,  to be strep in her vagina.  her boyfriend had received oral sex from a woman with strep throat and passed it on to my friend.  Is it possible that the virus in my throat was transfered to this woman and was confused for chlamydia?

4. Do I or my partner need to notify our other sexual partners from the last year?


We are both just really confused--thank you so much for your help

[H. Hunter Handsfield, M.D.]

Another comment, not directly pertinent to your questions:  I am a bit perplexed by your partner having protected vaginal but unprotected anal sex.  STD risks are just as high, generally even higher, with anal than vaginal intercourse.  It doesn't matter a whole lot for oral sex, although even there it would provide an increased measure of protection, given your conscious choice of a sexual lifestyle that is high risk from an STD standpoint.

[H. Hunter Handsfield, M.D.]

It's hard to second guess a third party's test result--it would be difficult enough to do that even if you had more direct information.  Some older chlamydia tests (less used than in the past but still used by some labs, lower cost) are prone to false positive results.  And it would be a slightly surprising event to have 2 separate infections simultaneously, presumably both chlamydia and a bacterial UTI.  The other factor is the reliability that she was a virgin before all this, because catching chlamydia from your partner, if indeed he used a condom for vaginal sex, is highly improbable.  So if she has it, I would assume that in fact she has had other partners.

There is no way I can sort all this out.  Most likely you and your partner both can rely on your negative chlamydia tests, especially if ae newer (DNA amplification) test was used; those tests are highly sensitive and don't miss many infections.  Of course, you or your partner could have been infected and had spontaneous clearing.  So my main bottom line is "Who knows?"

As to your specific questions:  1 and 2, see above.

3) The type of streptococcus that causes strep throat (typically group A strep) is an entirely different organism from the one that sometimes causes vaginal infection (usually group B).  Even if one of you had an atypical strep, that scenario is a distant stretch.  I would disregard it.

4) From the strict perspective of medical and transmission risks, I see no reason to inform your other partners.  But take into consideration the social context:  if they learn about these events they might believe that out of special caution and courtesy, they should have been told.  So it's up to you.

Bottom line:  The most likely scenarios seem to be either that her chlamydia test was false positive, or that she was not truthful about other partners--i.e., that her infection isn't related to sex with your partner.  (With one caveat:  As you likely know, UTI can be triggered by sex--not an STD, but the result of "massaging" bacteria into the urethra.  That's what "honeymoon cystitis" is all about.  But your partner has no biologic or ethical responsibility for that.)

I hope this helps.  Best wishes--  HHH, MD