Do the transporters screen out viruses or not? A virus is defined in my Concise Oxford as being "a microscopic organism consisting mainly of nucleic acid in a protein coat, multiplying only in living cells and often causing diseases". Often, but not always. We are actually crawling with bacteria and generally yucky stuff, but they are good for us. In the instance of Angel One, my theory is that the virus was so similar in type and construction to, er, stuff that we carry around with us habitually that the transporter let it through. One might ask why Crusher didn't beam someone from one room to another to remove the virus. Well, one might respond that she probably did, it may have been the first thing she tried, but it doesn't seem to have worked. Mind you, even if it had worked, what then? Would you have then had a freeform virus floating around the Enterprise? When people are in the transport beam, where exactly are they? Do they go from A to B by the most direct route, do they go into hyperspace, another dimension, or what? Data states in "The Best of Both Worlds Part Two" that they go into a subspace domain. What's one of them? And is it full of viruses that have been screened out by the 'sporters?
All of which has got precisely nothing to do with this episode. The only odd note was when one of the guys was threatening to kill Riker. Picard's response was to go into a face-off with someone he'd been told by his own Chief Medical Officer was a drug addict. Does that sound sensible to you?