I am in a similar predicament currently, and though I am too late for the original poster, hopefully I can help others.
Basically, almost every country on the planet has agreed, through the World Health Organization (WHO) to various rules and procedures regarding treatment of health and infectious disease threats. You need to get an official doctors statement explicitly stating that you are healthy and within compliance with these rules. These two websites should give you the background you need:
Wikipedia article: http://en.wikipedia.org/wiki/International_Health_Regulations
World Health Organization website: http://www.who.int/ihr/en/
I have not gone through this with the Spanish consulate yet, but I assume I only need a signed document explicitly stating that I am healthy according to the International Health Regulations 2005 as set forth by the WHO. I will update as I know more. I plan to contact the consulate in a few days about this.
EDIT: I don’t know how or where I found this, but I was jumping between the US department of State Travel website, the CDC website, and the WHO website, but it appears that the link below may lead to the form needed. I am still going to talk to the Spanish consulate to confirm, but I imagine that this is what they want. As I said, I’ll keep everyone updated.
http://www.who.int/ihr/travel/icvp/en/index.html