Background: Novel swine-origin influenza A pandemic 2009 (H1N1) virus (S-OIV) infection in the context of other respiratory viruses circulating in winter has not been studied.
Methods: Clinical and microbiologic data were collected prospectively from 444 consecutive patients presenting with an influenza-like illness (ILI) to a large pediatric hospital at the beginning of the S-OIV outbreak in Australia.
Results: Of 444 patients, 119 had polymerase chain reaction-confirmed S-OIV. Influenza A virus was detected by direct immunofluorescence in only 69 of these. Overall, inadequate respiratory samples were more common with rayon than flocked swabs (P = 0.01). The mean age of patients with S-OIV was higher than those with another cause of an ILI (10.2 vs. 6.4 years; P < 0.0001). The commonest symptoms in S-OIV were fever (93%) and cough (92%), followed by coryza (78%), sore throat (72%), headache (59%), myalgia (49%), vomiting (23%), and diarrhea (16%). Clinical features did not discriminate between patients with S-OIV and those with another ILI, except headache and myalgia, which were more common in children younger than 5 years who had S-OIV than those who did not (headache: P < 0.0001; myalgia: P = 0.0004). More patients with S-OIV had contact with a confirmed case but contact history had insufficient positive predictive value (44%) and negative predictive value (78%) for identifying S-OIV. Only 2% of the patients had a history of travel, and only 1 of these had S-OIV.
Conclusions: A clinical case definition is unlikely to be useful for discriminating patients with S-OIV from those with another cause of an ILI during winter. Direct immunofluorescence for influenza A cannot be used alone to reliably detect S-OIV.
From the *The Royal Children's Hospital Melbourne, Parkville, Victoria, Australia; †Department of Paediatrics, The University of Melbourne, Parkville, Victoria, Australia; ‡Murdoch Children's Research Institute, Parkville, Victoria, Australia; and §Victorian Infectious Diseases Reference Laboratory, Royal Parade, Parkville, Victoria, Australia.
Accepted for publication March 5, 2010.
All authors declare that they have no competing interests.
Address for correspondence: Nigel Curtis, MA, MB BS, DCH, DTM&H, MRCP, FRCPCH, PhD, Department of Paediatrics, The University of Melbourne, The Royal Children's Hospital Melbourne, Parkville, Victoria 3052, Australia. E-mail: firstname.lastname@example.org.
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