It's not hard solo but i think there is an issue when grouped. I have never had any problem when I played solo, but when I was in a group, some people never did get infected.
I ran one of my alts through it last night, solo. I got infected in about 5 minutes.
This is my opinion as well. With my solo chars it took me 3 mins max every time I've done it. When I'm grouped with my wife it's always a pain. One of the times we had to reset the timer 5 times (yes 5, and yes we were at the right place...I had done that quest 5 times by then...) and then we decided to abandon the mission and pick it back up. I got infected right away (after the rakghoul hit me, of course
) but it took her another 45 mins to get hers (she got it reght away when she abandoned and got the mission a third time)