I see no one has responded yet to your concerns about HIV or Hep in children from Africa(or anywhere else for that matter) so I'll jump in
. Children are tested numerous times (I think most are tested at LEAST 3 times before adoption is finalized) in most countries where there is a higher risk of HIV & Hep.
My understanding is that you can not adopt children internationally who have tested positive for HIV...but that info may be incorrect now. The testing is up to US standards, and if you have concerns you can pay to have the child retested to US stardards to be sure.
The children in Ethopia can come home at an early age(under 12 months usually) and are in great settings with good caregiver ratios...so are in foster homes as well.
Best of luck finding the program that is right for you
P.S. You might want to check out Vietnam too
they have newly reopened program at the moment with lots of infant referrals.