What circumstances might cause an sti/std to be transmitted to a person receiving a handjob?

The hands doing the job or yours were placed close to her ureteral meatus or yours. And bugs worked their way up to your. I the jobber had syph and hand ulcer hand could be it as well. Or if they did not wash hands between job. Best to get tested.

It is not possible unless your had injury to the penis (cut or abrasion) and the hand had the organism causing STD both extremely far fetched. So relax and if worried dont indulge in sex with persons you dont trust or know to avoid worries like that