Kirill Sidelnikov claims his positive steroid test came from using Russian nasal spray. His story is he injured his nose while training then used the spray a doctor gave him. The lesson here is you should never listen to a Russian doctor.
Seriously, though, it must be difficult to be a foreign athlete who competes in the United States. Our concepts of drugs and medicine are totally different. Here it's basically illegal to say the word steroid if you're an athlete. Meanwhile in many other countries, the performance enhancing drugs we demonize are actually used for medicinal purposes.
I'm not saying I totally believe him, but I do see how easy it would be to mess up, especially when a doctor prescribes something for an injury.