hello, i posted this on the expert forum, as an additional comment to an exisiting thread. whilst strictly speaking it might have been in violation of the forum rules, i think that the question is a general one which merits an answer, so maybe someone can check out with the docs to see what they think:
the general understanding is that condom protected (vaginal) sex is safe, unless the condom fails/splits/tears/rips, in which case this would be visible to the naked eye. however, i have read that condoms can be defective in manufacture i.e. have small holes which pass the testing phase, and that these small holes would need a microscope to be seen. this is because manufacturers do not test every single condom, but only samples from each batch/lot. moreover, there must be a certain number of defective condoms in each batch/lot, for the batch/lot to be discarded.
this is the link: http://www.infoforhealth.org/pr/h9/h9chap4_4.shtml