Complex sentence: Tropical sprue is largely limited to regions about 30 degrees north and south of the equator, therefore recent travel to these regions is a key factor in diagnosing this disease.
Split into simpler sentences: Tropical sprue is largely limited to regions about 30 degrees north and south of the equator. Therefore, if one resides outside of that geographical region, recent travel to the region is a key factor in diagnosing this disease.