Sexual Network of a high school and hepatitis B..

Hehe..the only thing that i can remember from a grand round today apart from the core antigens for hepatitis bla bla was a diagram of sexual network of a high school. Dr.H said that the main problem of hepatitis B is that it is sexually transmitted and sex is complex. She showed us a diagram of a perfect couple with only two dots;man and woman. And she said that in that case its simple. U can find or detect the culprit in any of them It would not be a big problem. But if the sexual network is like the diagram below, u would be in such a big trouble..
-Picture taken in http://www.primidi.com/2005/01/27.html

How would u find the culprit here?Most of them enjoy one night stand and change their partner regularly.... And , yeah, most of them wont wore condom during the sexual intercourse..so? the viral can be transmitted readily...huhu..
And Dr.H also said that there were only few persons detected as highly infectious for hep B in Cork. And two of them were insignificant now as one was dead and the other one had emmigrate to other part of the world. I think she kinda knew who the highly infectious people are as she said that she wanted to print their picture out and asked her patients whether they knew these people or not. But then she said that it will be really time consuming (and a bit unethical??) and she wont really have enough time to do that..
=)

P/s: Sorry ye kalau di hari raya saya bercakap sal mende ngarut...hehe..Hepatitis B..hahaha