count the number of patients for whom chlorhexidine gluconate was prescribed during the same month after they had been diagnosed with acq cardiac septl defect since 2101.
select count( distinct t1.subject_id ) from ( select admissions.subject_id, diagnoses_icd.charttime from diagnoses_icd join admissions on diagnoses_icd.hadm_id = admissions.hadm_id where diagnoses_icd.icd9_code = ( select d_icd_diagnoses.icd9_code from d_icd_diagnoses where d_icd_diagnoses.short_title = 'acq cardiac septl defect' ) and strftime('%y',diagnoses_icd.charttime) >= '2101' ) as t1 join ( select admissions.subject_id, prescriptions.startdate from prescriptions join admissions on prescriptions.hadm_id = admissions.hadm_id where prescriptions.drug = 'chlorhexidine gluconate' and strftime('%y',prescriptions.startdate) >= '2101' ) as t2 on t1.subject_id = t2.subject_id where t1.charttime < t2.startdate and datetime(t1.charttime,'start of month') = datetime(t2.startdate,'start of month')