"I take it you've seen this article from Emily Oster at Harvard, on this subject."
http://www.people.fas.harvard.edu/~eoster/hepb.pdf
Yes, I heard Oster present this paper last year. At her seminar, I mentioned the possible connection of hepatitis B to testosterone levels at conception. There are factors other than hepatitis B affecting hormonal balance that also appear to have similar consequences for sex ratio.