It comes from SNOMED, which is a system for electronic health records and is very comprehensive, multi-lingual & multi-national. Every disease, symptom, medical

It comes from SNOMED, which is a system for electronic health records and is very comprehensive, multi-lingual & multi-national. Every disease, symptom, medical term, etc... has a code which allows matching across languages. I doubt the IDs start at 1, it's likely the fist few digits (perhaps 8405) are a type classification for the ID. It's been going for a few decades and thousands of new IDs are added each year.