instruction: how many of the patients admitted on clinic referral/premature were treated with ampicillin-sulbactam?
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN prescriptions ON demographic.hadm_id = prescriptions.hadm_id WHERE demographic.admission_location = "CLINIC REFERRAL/PREMATURE" AND prescriptions.drug = "Ampicillin-Sulbactam"