what is the average number of patients diagnosed with acute lung edema nos monthly since 2100?
select avg(t1.c1) from ( select count( distinct diagnoses_icd.hadm_id ) as c1 from diagnoses_icd where diagnoses_icd.icd9_code = ( select d_icd_diagnoses.icd9_code from d_icd_diagnoses where d_icd_diagnoses.short_title = 'acute lung edema nos' ) and strftime('%y',diagnoses_icd.charttime) >= '2100' group by strftime('%y-%m',diagnoses_icd.charttime) ) as t1