The health sector comprises 17 specialized hospitals and centers, 4 regional diagnostic and treatment centers, 9 district and 21 aimag general hospitals, 323 soum hospitals, 18 feldsher posts, 233 family group practices, 536 private hospitals, and 57 drug supply companies/pharmacies. In 2002, the total number of health workers was 33,273, of whom 6823 were doctors, 788 pharmacists, 7802 nurses, and 14,091 mid-level personnel. At present, there are 27.7 physicians and 75.7 hospital beds per 10,000 inhabitants.. How many more specialized hospitals and centers is the health sector comprised of than district hospitals?