Ahh, but is that a problem inherent in prostitution itself? Or is that a problem caused by the illegalization of prostitution? I firmly believe that it is the latter.
Crime rings form around pot distribution. But you don't see crime rings forming around the distribution of beer or cigarettes (well, there were quite a few crime rings attached to beer, but that also happened to be during the time of the Prohibition in the United States; coincidence?). By abusing the force of law to shut off supply without cutting down the demand and thus criminalizing anyone still involved in the business, it drives something that is normally not associated with the criminal world to associate itself with the criminal world. Perhaps one of our Dutch friends can back this up; is there a lot of crime associated with prostitution over there? I would guess not.
Granted, the second it becomes legalized, problems won't go away overnight. It will take time for those links to crime to slowly break away and for government to assert its control, but if you are worried about crime, then prostitution legalization and drug legalization is the BEST way to deal with the problem. It's slightly counter-intuitive, yes, but it's the lesson that history has been trying to teach us.
You can also get infections from working in hospitals, fighting in wars, traveling in the jungle, going to Africa, etc. It just so happens that some of the STDs (esp. AIDS) are rather nasty, but aside from that, diseases from sexual contact are no more unique than diseases from other forms of contact. And the risk of STDs is precisely the reason why legalization is important because it will allow government to enter the arena and impose standards, health inspections, etc.