I read false positives for chlamydia are rare, but still can in fact happen- can you give scenario of how it could happen?

Type of test done: The most accurate and most common chlamydia tests use nucleic acid amplification and almost never are falsely positive. There is also a "DNA probe" test, less costly and still done by some labs, which sometimes give false pos results. However, even here the large majority of positves are true. If two partners have neg and pos results, usually the negative is false. Both partners need treatment.