I had a look through the game files with FrostyEditor, and it seems there are two conditions in order to trigger this task.
One is talking to the Turian doctor.
Second is scanning the plant behind the stoners.
Once you do that, the task Running a Fever should pop up in your journal and on screen...supposedly. However, I tried it and it doesn't.
That is correct. It seems that it (for whatever reason) was removed with the hotfix that solved a crash when you got close to the stoners house.
Shame, because I've read the lines for the next part and it's pretty funny.
