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. 2011 Jun 15;203(12):1739-47.
doi: 10.1093/infdis/jir187.

Complications and outcomes of pandemic 2009 Influenza A (H1N1) virus infection in hospitalized adults: how do they differ from those in seasonal influenza?

Nelson Lee  1 , Paul K S Chan, Grace C Y Lui, Bonnie C K Wong, Winnie W Y Sin, Kin-Wing Choi, Rity Y K Wong, Elaine L Y Lee, Apple C M Yeung, Karry L K Ngai, Martin C W Chan, Raymond W M Lai, Alex W Y Yu, David S C Hui
Affiliations

Complications and outcomes of pandemic 2009 Influenza A (H1N1) virus infection in hospitalized adults: how do they differ from those in seasonal influenza?

Nelson Lee et al. J Infect Dis. .

Abstract

Background: It is unclear whether pandemic 2009 influenza A (pH1N1) infection caused more significant disease among hospitalized adults than seasonal influenza.

Methods: A prospective, observational study was conducted in adults hospitalized with polymerase chain reaction-confirmed pH1N1 infection in 2 acute-care general hospitals from June 2009 to May 2010 (n = 382). Complications and outcomes were described and compared with those in a seasonal influenza cohort (2007-2008, same hospitals; n = 754).

Results: Hospitalized patients with pH1N1 influenza were younger than those with seasonal influenza (mean age ± standard deviation, 47 ± 20 vs 70 ± 19 years) and fewer had comorbid conditions (48% vs 64%). The rate of positive immunofluorescence assay results was low (54% vs 84%), and antiviral use was frequent (96% vs 52%). Most patients in both cohorts developed complicated illnesses (67.8% vs 77.1%), but patients with pH1N1 influenza had higher rates of extrapulmonary complications (23% vs 16%; P = .004) and intensive care unit admission and/or death (patient age <35 years, 2.3% vs 0%; 35-65 years, 12.4% vs 3.2%; >65 years, 13.5% vs 8.5%; adjusted odds ratio [OR] 2.13; 95% confidence interval [CI], 1.25-3.62; P = .005). Patients who received antiviral treatment within 96 h after onset had better survival (log-rank test, P < .001). However, without timely treatment, the mortality risk was higher with pH1N1 infection (9.0% vs 5.8% for seasonal influenza; adjusted OR, 6.85; 95% CI, 1.64-28.65; P = .008]. Bacterial superinfection worsened outcomes.

Conclusions: Adults hospitalized for pH1N1 influenza had significant complications and mortality despite being younger than patients with seasonal influenza. Antiviral treatment within 96 h may improve survival.

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