syphilis testing

According to a past post you state that 6 weeks is long enough to have a reliabe test for syphilis, however the incubation period is up to 90 days.  Will the test pick up incubating syphilis or is it highly unusual to have incubating syphilis past 6 weeks.  I tested negative at 6 weeks and then again at 11 weeks, however I developed a sore in my mouth which appeared to be a canker sore 2 days after testing and was wondering how likely that I still had incubating syphilis and what a Chancre sore in the mouth would look like.  Thanks for answering my question.

[H. Hunter Handsfield, M.D.]

Sometimes it can take as long as 3 months for the syphilis blood test to become positive; but more than 90% will be positive within 6 weeks.  Almost certainly you have a garden-variety canker sore, not syphilis.  In general, the chancre of syphilis is painless and has a firm, "solid" feel to it (often described as "rubbery").  Canker sores generally are "soft", not firm/rubbery, and quite painful.

Anyway, 11 weeks is long enough to be considered reliable, even if a bit short of 3 months.  But if the lesion is like my description of syphilis, or if you have reason to believe the person you were exposed to actually has syphilis, follow up with a health care provider for further evaluation.

HHH, MD