Abstract
IntroductionThere is conflicting data as to whether obesity is an independent risk factor for mortality in severe pandemic (H1N1) 2009 influenza (A(H1N1)pdm09). It is postulated that excess inflammation and cytokine production in obese patients following severe influenza infection leads to viral pneumonitis and/or acute respiratory distress syndrome.MethodsDemographic, laboratory and clinical data prospectively collected from obese and non-obese patients admitted to nine adult Australian intensive care units (ICU) during the first A(H1N1)pdm09 wave, supplemented with retrospectively collected data, were compared.ResultsOf 173 patients, 100 (57.8%), 73 (42.2%) and 23 (13.3%) had body mass index (BMI) <30 kg/m2, ≥30 kg/m2 (obese) and ≥40 kg/m2 (morbidly obese) respectively. Compared to non-obese patients, obese patients were younger (mean age 43.4 vs. 48.4 years, p = 0.035) and more likely to develop pneumonitis (61% vs. 44%, p = 0.029). Extracorporeal membrane oxygenation use was greater in morbidly obese compared to non-obese patients (17.4% vs. 4.7%, p = 0.04). Higher mortality rates were observed in non-obese compared to obese patients, but not after adjusting for severity of disease. C-reactive protein (CRP) levels and hospital length of stay (LOS) were similar. Amongst ICU survivors, obese patients had longer ICU LOS (median 11.9 vs. 6.8 days, p = 0.017). Similar trends were observed when only patients infected with A(H1N1)pdm09 were examined.ConclusionsAmong patients admitted to ICU during the first wave of A(H1N1)pdm09, obese and morbidly obese patients with severe infection were more likely to develop pneumonitis compared to non-obese patients, but mortality rates were not increased. CRP is not an accurate marker of pneumonitis.
Highlights
There is conflicting data as to whether obesity is an independent risk factor for mortality in severe pandemic (H1N1) 2009 influenza (A(H1N1)pdm09)
Critical care data from the first pandemic influenza wave of 2009 (hereafter A(H1N1)pdm09) in Australia and New Zealand revealed that 28.6% of patients admitted to intensive care units (ICUs) were obese [1], an observation not noted previously in severe influenza infection [2,3]
This study aims to describe the demographic characteristics and outcomes of obese patients with severe influenza infection during the first A(H1N1)pdm09 wave in Australia; and to determine the relationship between body mass index (BMI), C-reactive protein (CRP) and viral pneumonitis in severe influenza infection
Summary
There is conflicting data as to whether obesity is an independent risk factor for mortality in severe pandemic (H1N1) 2009 influenza (A(H1N1)pdm). Post hoc analysis revealed that the rate of obesity (BMI $30 kg/m2) in ICU patients (44%) was much higher than in the general Australian and New Zealand adult population (23.7%–27.1%) [4,5]. This is comparable to data from the United States of America (USA), where 51% of patients hospitalized during the first pandemic phase in California had BMI $30 kg/m2, 2.2 and 1.5 times the prevalence of obesity in California and the USA respectively [6]. Influenza infection in obese mice deregulates immune responses, and results in mortality rates six times higher [8]. The effect of the adipokines adiponectin and leptin, and cytokines on inflammatory cells (T-cells and monocytes/macrophages) in the obese population infected with severe influenza during a pandemic, is less well studied
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