You are participating in a medical mission in South America and are seeing a 11yo boy who is brought in by his mother.  He has been complaining of joint pain and fever for the past 2 weeks.  She tells you that it seems to “move” from joint to joint over this time and nothing seems to help.  She does report that he has seemed to be sick for 4-6 weeks with various “cold” symptoms, but they didn’t seem too severe.  On examination, he has temperature of 101.2^oF and the below rash.

What should be your concern and what criteria can help make the diagnosis?