instruction: how many patients were tested until 2 years ago for sputum, tracheal specimen?
response: SELECT COUNT(DISTINCT patient.uniquepid) FROM patient WHERE patient.patientunitstayid IN (SELECT microlab.patientunitstayid FROM microlab WHERE microlab.culturesite = 'sputum, tracheal specimen' AND DATETIME(microlab.culturetakentime) <= DATETIME(CURRENT_TIME(), '-2 year'))