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

Abstract

Objective: 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.

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

Results: 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)

Conclusion: 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.