United Kingdom first wave ( May outcome with pandemic A / H 1 N 1 influenza : Risk factors for hospitalisation and poor

Background During the first wave of pandemic H1N1 influenza in 2009, most cases outside North America occurred in the UK. The clinical characteristics of UK patients hospitalised with pandemic H1N1 infection and risk factors for severe outcome are described. Methods A case note-based investigation was performed of patients admitted with confirmed pandemic H1N1 infection. Results From 27 April to 30 September 2009, 631 cases from 55 hospitals were investigated. 13% were admitted to a high dependency or intensive care unit and 5% died; 36% were aged <16 years and 5% were aged $65 years. Non-white and pregnant patients were overrepresented. 45% of patients had at least one underlying condition, mainly asthma, and 13% received antiviral drugs before admission. Of 349 with documented chest x-rays on admission, 29% had evidence of pneumonia, but bacterial co-infection was uncommon. Multivariate analyses showed that physician-recorded obesity on admission and pulmonary conditions other than asthma or chronic obstructive pulmonary disease (COPD) were associated with a severe outcome, as were radiologically-confirmed pneumonia and a raised C-reactive protein (CRP) level ($100 mg/l). 59% of all in-hospital deaths occurred in previously healthy people. Conclusions Pandemic H1N1 infection causes disease requiring hospitalisation of previously fit individuals as well as those with underlying conditions. An abnormal chest x-ray or a raised CRP level, especially in patients who are recorded as obese or who have pulmonary conditions other than asthma or COPD, indicate a potentially serious outcome. These findings support the use of pandemic vaccine in pregnant women, children <5 years of age and those with chronic lung disease. INTRODUCTION On 11 June 2009 the World Health Organization announced the first influenza pandemic of the 21st century. 2 While most pandemic H1N1 infections were mild or subclinical, the case fatality rate was 0.1e0. 7%. 4 Early reports suggested a case hospitalisation rate of 2e8%, later moderated to approximately 1% in view of under-ascertainment of mild cases. Although atypical, patients with severe disease imposed a considerable burden on hospital systems. Hospitalisation due to pandemic H1N1 infection was most common in children, teenagers and younger adults. At least half had underlying medical conditions. 2 8e12 Relatively few studies have examined the risk factors associated with a severe outcome. 13 METHODS Data collection The Influenza Clinical Information Network (FLUCIN) surveillance network was established by the Department of Health in England on 11 May 2009. Clinical data were collected from 55 hospitals in 20 cities or towns (see figure 1 in online supplement). Trained FLU-CIN data collectors gathered information from the case notes of patients hospitalised with pandemic H1N1 infection without pre-selection. All patients had acute respiratory illness and pandemic H1N1 infection confirmed by real-time reverse-transcriptase PCR. Diagnostic tests were performed as dictated by clinical management. Data were extracted using a standard form that included demographic characteristics, past medical history, prehospital medication, clinical presentation, care timelines, initial assessment (emergency department and/or acute medical unit), investigations and care escalation from levels 0 to 3, discharge and death. Since height and weight are not uniformly recorded in UK hospital notes, obesity based on physicians’ observations was captured when recorded on admission. Analysis of data Anonymised data were analysed using STATA Version 10 (StataCorp). c or Fisher exact tests were used to assess differences in proportions and the ManneWhitney test was used for continuous variables. The demographic data were compared with those of the combined populations of London, East Midlands and Northern Ireland because these areas provided >75% of the FLU-CIN cases. As < Supplementary figures are published online only. To view these files please visit the journal online (http://thorax.bmj. com). For numbered affiliations see end of article. Correspondence to Professor J Nguyen-Van-Tam, Division of Epidemiology and Public Health, University of Nottingham, Clinical Sciences Building, City Hospital, Hucknall Road, Nottingham NG5 1PB, UK; jvt@nottingham.ac. uk Received 14 January 2010 Accepted 21 April 2010 This paper is freely available online under the BMJ Journals unlocked scheme, see http:// thorax.bmj. com/site/about/ unlocked.xhtml i Level 0: Patients whose care needs can be met through normal ward care. Level 1: Patients at risk of deteriorating or recently relocated from higher levels of care whose needs can be met on an acute ward with additional advice and support from the critical care team. Level 2: Patients requiring more detailed observation or intervention including support for a single failing organ system and those ‘stepping down’ from higher levels of care (high dependency unit). Level 3: Patients requiring advanced respiratory support alone or basic respiratory support together with support of at least two organ systems. This includes all complex patients requiring support for multiorgan failure (intensive care unit). Thorax 2010;65:645e651. doi:10.1136/thx.2010. 135210 645 Respiratory infection group.bmj. com on July 25, 2010 Published by thorax.bmj. com Downloaded from