interstitial lung pneumonitis disease history evidence active infectious pulmonary ild pneumonitis organizing fibrosis idiopathic pneumonia induced pulmonary history chest obliterans pneumonitis infectious non history steroids required current evidence active known composition compounds chemical similar attributed allergic reactions biologic history used oxygen air room pulse oximetry saturation supplemental rest dyspnea pulmonary severe infection immunodeficiency disease moderate pneumonia bacteremia hospitalization impairment complications