Excuse the typographical error. "...there is NO concern...." This includes artificial joints and other implants -- at least no STD has ever been known to do that.
Recurrent or persistent NGU is a frequent and often confusing problem, and the causes are not known. It is likely that not all recurrences are due to persistent or new infection, or to any infection at all. The initial NGU might be followed by inflammation that isn't due to infection, i.e. no persisting bacteria, virus, etc -- i.e., nothing that can be transmitted to a partner. (Note that inflammation -- which can cause white blood cells to appear in the urethra or urine -- and infection are not the same thing.)
Perhaps most important, recurrent NGU in men has never been shown to be a serious health problem -- i.e., no known consequences like infertility, urethral stricture, or health problems in affected men's female partners. And no, there is concern about an infection spreading to another part of your body. So whatever is going on, most likely it's nothing serious for either you or your partner. Once both you and your partner have been treated, probably nothing more need be done, especially for your partner.
There are no good explanations as to why inflammatory abnormalities in the urine might come and go. As to symptoms, you don't say which symptoms are persisting or recurring. If you are having definitely abnormal discharge of pus or cloudy mucus from your penis, then probably you indeed have urethritis. If only a little clear mucus, or if no discharge but only discomfort, most likely there is nothing you need to worry about.
As all this implies, there are lots of uncertainties. Most likely you do not need further treatment, and almost certainly your partner does not. But the direct advice of the providers in charge of you care is more reliable than anything I (or any distant online expert) can say. So continue to follow up with your docs. There's not much more this forum can offer you.
I hope this helps. However, please also note the MedHelp rule about a maximum of 2 questions every 6 months (on the moderated forums), to permit space for others to ask new questions. This is your second in the past week.
Best wishes-- HHH, MD
Thank you - I appreciate your response and will leave this forum for others going forward. I would like to clarify your statement above "And no, there is concern about the infection spreading to another part of your body.." I assume you meant that this is not a risk. Is this correct? Does this also apply to artificial joints where the risk of infection is understood to be higher?
Thanks again