That sucks, man
Dear learningtoplay,
First, let me offer my concern and condolences to you on this event. Also, I commend you for raising this topic on the forum; others would not be so forthcoming. Chlamydia is not lethal and is very treatable if caught early, but it is nonetheless a shock and a tremendous strain on an S.O. relationship. At least you were "lucky" and experienced symptoms - chlamydia can be asymptomatic and therefore many people are probably walking around with a disease that they will undoubtedly spread to future sexual partners.
Ignore the agency - They will lie to protect their business and you cannot rely on anything they tell you. They don't care what happens to your health, your SO's health, or your relationship with her. They just want you to keep using their services. No agency (or independent SP) will admit to being the source of infection. Sometimes they truly don't know and other times they know and continue working while receiving treatment (or awaiting test results). Either way, it's easier to assign blame to the john's other partners, be they SOs or SPs. You did the honourable thing and told both the girl and the agency. Your obligation ends after that point.
I am most concerned, however, about the actions of Public Health. My admittedly incomplete understanding of the process is that chlamydia is a reportable disease, one of 48 in Canada that range from chickenpox to West Nile to HIV. Data on reportable diseases is collected in order to establish incidence rates, and therefore to see if incidence rates are increasing - a sign of an outbreak and/or a failure in containment policies (vaccination, sanitation, awareness, etc.)
Normally, doctor-patient confidentiality is paramount, but there are several exceptions. From the Canadian Medical Association's Code of Ethics:
"Disclose your patients' personal health information to third parties only with their consent, or as provided for by law, such as when the maintenance of confidentiality would result in a significant risk of substantial harm to others or, in the case of incompetent patients, to the patients themselves. In such cases take all reasonable steps to inform the patients that the usual requirements for confidentiality will be breached."
In the case of STDs, HIV is a prime example. A phyisician is allowed to seek out and inform your sexual partners if you test positive and if he/she informs you of the process described above. Still, I believe they only inform your partner if they have reason to believe that you will not.
What appears to have happened in your case is a bit different - it is a public health policy known as "partner notification" and as you are well aware, it seems to occur independently of the physician-patient relationship.
Two useful links (both pertaining to HIV, though) are:
http://www.health.state.ny.us/diseases/aids/regulations/notification/hivpartner/reportquest.htm
http://www.aidslaw.ca/Maincontent/issues/testing/e-info-ta18.htm
The Ontario Ministry of Health and Long-Term Care has an "STD Control Protocol" that they follow and which I believe contains information on how partner notification is performed. I was unaware that chlamydia was part of this program, and I could not find an on-line version of this document to review for you. Therfore, I won't weight in too much on either side, other than to say that as you describe it, the notification process could definitely have been handled with greater care and sensitivity. Such boorish behaviour is really quite counterproductive on the part of Public Health - stories like this only serve to dissuade people from getting tested.
This is why clinics such as the HassleFree in Toronto are so popular. There is a level of protection and confidentiality not possible at other clinics. They will not call your wife if you get chlamydia or gonorrhea, but they still ask about S.O. relationships and the level of safe sex with your S.O., and they will insist that you use condoms with all current sexual partners until your test results come back. With HIV+, I don't know exactly what they do with a positive test. Being non-judgemental and confidential, they would likely choose a counselling- and support-based approach geared towards convincing you to tell your past sex partners, rather than taking unilateral action.
Good luck,
Bizkit