I've yet to be convinced that Jenner did reveal everyone was a carrier to Rick. Everything that points to him knowing can also be explained away, as this thread has shown. Given how the group have started to notice the dead rising without being bitten, it looks like we'll get an answer as to whether Rick knows fairly soon.
Also even though it has almost nothing to do with the group I'd like to find out what happened to the ISS Astronauts. If they weren't evacuated when the plague first started they could still be alive at this point since, at least by "TS-19" the plague only has been global for 63 days. They haven't even spent a full month at the farm yet.
Maybe the Astronauts would be in contact with survivor colonies, maybe some major islands survived totally intact like Hawaii or Guam.
If you haven't already, check out Max Brook's 'World War Z'. It features exactly the situation you describe with the ISS astronauts.