[1] Boston Univ, Dept Med, Sect Pulm Allergy Crit Care, Sch Med, Boston, MA 02118 USA
[2] Permanente Med Grp Inc, Oakland, CA USA
[3] Kaiser Permanente Northern Calif, Div Res, Oakland, CA USA
[4] Stanford Univ, Biomed Informat Dept, Palo Alto, CA USA
[5] Stanford Univ, Dept Med, Palo Alto, CA USA
[6] Kaiser Permanente Bernard J Tyson Sch Med, Dept Hlth Syst Sci, Pasadena, CA USA
[7] Univ Calif San Francisco, Dept Med, San Francisco, CA USA
[8] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA USA
[9] Boston Univ, Div Pulm Crit Care & Allergy, Sch Med, 72 E Concord St,R-304, Boston, MA 02118 USA