About 2 months ago I had unprotected vaginal sex with Woman A.  This was a one time occurance.  One week later I started a new relationship with Woman B, and we are currently in a sexual relationship with routine unprotected vaginal and oral sex.  A couple of days after my sexual encounter with Woman A, I experienced a slight burning in my penis during urination, but I sometimes get this with new sexual partners so I didn't think anything of it.  

About 2 months after my first encounter with Woman A, and starting the new relationship with Woman B, i experienced heightened itching and burning in my urethra, followed by discharge one week later.  I went in for an STD test which came back positive for Mycoplasma Genitalium.  

My question is, is it possible that I contracted MG from Woman A?  I only had sex with her one time and it seems strange that the extreme symptoms and discharge would happen 2 months later.  But I was with Woman B regulary only a week after being with Woman A, and the discharge only happened within the last week.  What is the time line of the "incubation period" for MG?  There does not seem to be much information about MG and I am not even certain that it is an STD? 

Mycoplasma genitalium is an organism which has been studies for only the past 20-30 years. It is very difficult to culture and tests have been available for research purposes for only the past decade and the role of the organism as an STI is still under intensive study.  We do know that it is sexually transmissible and the there is an association of the infection with urethritis (penile irritation) in men.  We also know that it is not usually tested for but in large studies only 10-20% of infections are symptomatic and, since testing is neither widespread nor routine (there are not currently available FDA-approved tests for Mg) most infections are undetected.  I agree that a single exposureis unlikely to lead to infection but it is certainly possible.  It is equally or perhaps even more likely that your current partner has the infection an is unaware and untested.  Put another way, there is just no way to know where your infection came from and trying to figure it out is a waste of time. In your situation, my advice is as follows:

1.  Both women should be informed of your infection and seek evaluation, telling them that you experienced symptoms, were tested and found to be infected .  You should also tell them that an expert (me) told you that most infections are asymptomatic and there is no way to know how long the infection has been present.

2. Treatment for Mg is azithromycin however, studies at showing that an increasing proportion of Mg infections are resistant to this drug and instead a drug called moxifloxacin, given for 5-10days is being used increasingly.  Unfortunately, moxifloxacin is more expensive than azithromycin.

I hope this information is helpful.  EWH