 A United Kingdom investigation of risk factors for hospitalisation and poor outcome with pandemic A / H1N1 influenza looked at 631 patients from 55 hospitals admitted with confirmed infection from May through September 2009 . 13 % were admitted to a high dependency or intensive care unit and 5 % died ; 36 % were aged < 16 years and 5 % were aged ≥ 65 years . Non @-@ white and pregnant patients were over @-@ represented . 45 % of patients had at least one underlying condition , mainly asthma , and 13 % received antiviral drugs before admission . Of 349 with documented chest x @-@ rays on admission , 29 % had evidence of pneumonia , but bacterial co @-@ infection was uncommon . Multivariate analyses showed that physician @-@ recorded obesity on admission and pulmonary conditions other than asthma or chronic obstructive pulmonary disease ( COPD ) were associated with a severe outcome , as were radiologically confirmed pneumonia and a raised C @-@ reactive protein ( CRP ) level ( ≥ 100 mg / l ) . 59 % of all in @-@ hospital deaths occurred in previously healthy people . 
