RT Journal Article SR Electronic T1 Positive correlation between swine-origin influenza A (H1N1) virus infection and severe respiratory disease JF Thorax JO Thorax FD BMJ Publishing Group Ltd and British Thoracic Society SP 172 OP 172 DO 10.1136/thx.2009.127449 VO 65 IS 2 A1 N Kakkar YR 2010 UL http://thorax.bmj.com/content/65/2/172.abstract AB