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.
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.
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.
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: email@example.com.
Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (www.pidj.com).