instruction: how many patients who have diagnosis icd9 code 28860 have dwell route of drug administration?
response: SELECT COUNT(DISTINCT demographic.subject_id) FROM demographic INNER JOIN diagnoses ON demographic.hadm_id = diagnoses.hadm_id INNER JOIN prescriptions ON demographic.hadm_id = prescriptions.hadm_id WHERE diagnoses.icd9_code = "28860" AND prescriptions.route = "DWELL"