Risk factors of A/H1N1 etiology in pneumonia and its impact on mortality

Pandemic flu has changed the epidemiology of pneumonia, thus challenging the prediction of etiology and outcome. We analyze the risk factors to predict influenza A/H1N1 infection in patients with pneumonia, and the impact of this etiology on mortality during a pandemic period. Differences between pneumonia with or without A/H1N1 coinfection are described.

Retrospective observational study in 364 consecutive patients hospitalized with pneumonia during the A/H1N1 pandemic flu, April-December 2009.

294 patients (80.5%) had A/H1N1(-) pneumonia, 47 (13.2%) A/H1N1(+) pneumonia, and 23 (6.3%) coinfection. Mortality during hospitalization was 24/294 (8.2%), 8/47 (16.7%), 2/23 (8.7%) respectively. A regression logistic analysis (Area under curve, AUC 0.81) to predict A/H1N1(+) pneumonia identified four independent variables: age < 60 years (Odds ratio, OR 5.9), multilobar infiltrates (OR 7.7), C-reactive protein (CRP) < 10 mg/dL (OR 2.8), and leukopenia < 5000/mm(3) (OR 3.4). Risk factors for in-hospital mortality in the whole group were A/H1N1 (+) etiology and LDH > 600 IU/L (OR 4.1) when adjusting for PSI, and hypoxemia (OR 4.2) when adjusting for CURB 65 (AUC 0.81). Heart disease (OR 27.4) and LDH > 600 IU/L (OR 10.5) were risk factors for in-hospital mortality in A/H1N1(+) patients (AUC 0.81)

Leukopenia, multilobar infiltrates, CRP<10 mg/dl and age < 60 years were independently associated with A/H1N1(+) etiology. Pandemic A/H1N1(+) increased mortality pneumonia. Heart disease and LDH > 600 were independently associated with mortality in A/H1N1(+) pneumonia.