I am reading a paper and it has a bit of mathematical notation that I need help with. I don't have a mathematics background therefore, I would really appreciate it if someone can help me with it. The formula is :

Can someone explain what ';' means in this formula. NB simply refers to negative binomial. Help would be appreciated.
I assume $\hat{x}$ is the mean and $\theta$ the standard deviation, so '$;$' in this context means 'with', 'given' or 'such that', similar to the vertical bar '$|$'.