Read this and answer the question. If the question is unanswerable, say "unanswerable".

Houston is the seat of the internationally renowned Texas Medical Center, which contains the world's largest concentration of research and healthcare institutions. All 49 member institutions of the Texas Medical Center are non-profit organizations. They provide patient and preventive care, research, education, and local, national, and international community well-being. Employing more than 73,600 people, institutions at the medical center include 13 hospitals and two specialty institutions, two medical schools, four nursing schools, and schools of dentistry, public health, pharmacy, and virtually all health-related careers. It is where one of the firstand still the largestair emergency service, Life Flight, was created, and a very successful inter-institutional transplant program was developed. More heart surgeries are performed at the Texas Medical Center than anywhere else in the world.

How many hospitals are outside of the Medical Center group of organizations?
unanswerable