[Question #233] HSV Culture Accuracy

36 months ago
Hello,

About 8 days after my last act of protected sex with a new partner, I noticed a dome-shaped bump on the top-side of the shaft of my penis, near the base. The bump was red, fleshy, not-painful, and if I remember correctly, when I tried to squeeze/pop it, a bit of viscous white goo (like you might find from a pimple) came out. I did not notice any ingrown hairs. I immediately took 1g of Valacyclovir, took another 1g 12 hours later, and a third 1g 12 hours after that. I continued to monitor the bump and it did not appear to get any worse or change in condition, other than when I irritated it further by scraping off skin while attempting to pop it. Later I noticed a small amount of slightly yellow fluid oozing out of the raw skin, similar to what I used to see when I would get a cold sore. (I have HSV-1)

I had a swab-culture test about 42 hours after I first noticed the bump. By then, the spot was forming a very thin area of new skin/scab. I don't believe the test was a PCR, the name on the website says "HSV CULTURE W-RFX TO TYPING". The results came back negative. My IGG test also came back negative, so if this were HSV-2 it would be my first exposure.

I've read conflicting information about how accurate cultures are. Some sources say 80-90% accuracy for an initial episode, others say 76% of cultures are false-negatives, others say 50-90% accuracy, others say even less based on time frame and whether the site is fluid-filled, an ulcer, or crusted over. Also at issue is the Valacyclovir interfering and that I have HSV-1 antibodies so any new outbreak might be too mild to generate a "typical" blister with enough virus.

Finally, my question: at this point, given the state of the lesion and the Valacyclovir, how much confidence can I place in the culture? If it were a PCR test, how much more confident could I be? 

Thanks!
Terri Warren, RN, Nurse Practitioner
Terri Warren, RN, Nurse Practitioner
36 months ago
Good morning Jonathan,
This single bump with white goo does not sound like herpes to me from your description but someone must have wondered if it might be in order to do a swab test from the bump.  In some ways, your description sounds more like something called molluscum.  You can look it up to see if it looks at all familiar.  Or it could be a simple pimple.  You are correct that if the bump is HSV 2, and this was new infection, your antibody test would be negative.  Compared to PCR, the false negative rate for PCR is around 75% in some studies.  And this does vary from study to study so I am not surprised that you are reading conflicting information. And yes a person with HSV 1 infection already will have a milder HSV 2 new infection and it will take a little longer to develop antibody.  The bigger problem I see is taking the Valtrex.  You may well have influenced the result of the swab test in addition to having an insensitive swab test.  So in summary, I think at this point, there is no way to know with any certainty what the bump was from your end.

However, the best way to sort this out would be to ask your partner to be tested for HSV 2.  Have you done that or thought about doing that?  If your partner is negative, and that is your only recent partner, and your partner has not had another recent partner, you can essentially rule out herpes as a cause of concern.

If the lesion was swabbed by PCR, it would be more sensitive but the Valtrex would also influence that swab result.

Terri
---
36 months ago
Hi Terri,

Thank you for your response. Just a quick point of clarification: When you wrote "Compared to PCR, the false negative rate for PCR is around 75%" you meant a regular culture achieves a false negative rate of 75% when the PCR would have detected HSV? 

I confirmed my swab was a non-PCR test. (My doctor did not think the lesion looked herpetic and the swab was at my request.) I did, however, take the Valtrex immediately, so it's possible that I prevented the bump from becoming a full-blown blister. My experience with coldsores is that even when I take Valtrex right away, I still get soreness and mild blistering, so I'm hoping that since I have no HSV-2 antibodies that the Valtrex would do even less and that the bump not getting worse is a good sign.

I've heard of molluscum, so I'm hoping the bump was that or a pimple--my concern is that I've never had bumps on my penis before and the timing is right in line with a new HSV infection.

I'm considering contacting my partner--I'm no longer seeing her. She did say she was tested (I don't know how recently), but I never specifically brought up herpes and I know that's not always included in panels.

Do you have any information on how effective condoms are at preventing herpes on the penis itself? The bump was under the area where a condom covers but near where it might slip past during sex or where you might touch yourself when removing the condom. And during one act we had brief external genital-genital contact before using the condom.

Thanks again.
Terri Warren, RN, Nurse Practitioner
Terri Warren, RN, Nurse Practitioner
36 months ago
Yes, for every four that PCR picks up, culture misses 3 (and that varies from study to study, but I am using one published by Dr. Morrow). 
Again, the studies on the benefits of condoms vary, but I think we would agree that condoms reduce transmission by about 50%.  The risk of a single encounter, even if the person did have herpes, is quite low - people who have herpes shed virus on about 13% of days sampled - so they don't shed every day.  And if she was shedding on the day you had sex and the condom slipped quite a bit, you wouldn't necessarily get infected for sure. 
You could contact the partner - give everyone a chance to say yes!  She might be concerned enough about your concern to get herself tested.  That's always a bit touchy, isn't it? 
I honestly think the chances that you would acquire herpes in your situation is quite low.  Certainly, if you want to do antibody testing you should wait about 12 weeks for the most accurate test.  You can get the test at 6 weeks if you wish and the result will be about 70% accurate - that is, there is a 70% chance that the result will stay the same as it is at the 6 weeks mark.  If you get any more bumps, you should most certainly have them swab tested right away and try to use a facility that can do PCR.  Most often the same swab is used for culture as for PCR, the difference is just what is requested on the lab form.  Many clinicians just don't know to order the PCR. 

Terri
---