Published 27 August 2009, doi:10.1136/bmj.b3403
Cite this as: BMJ 2009;339:b3403

Research

Monitoring the emergence of community transmission of influenza A/H1N1 2009 in England: a cross sectional opportunistic survey of self sampled telephone callers to NHS Direct

Alex J Elliot, project lead1, Cassandra Powers, scientist2, Alicia Thornton, scientist2, Chinelo Obi, research assistant2, Caterina Hill, epidemiologist2, Ian Simms, clinical scientist2, Pauline Waight, senior scientific information analyst2, Helen Maguire, regional epidemiologist3, David Foord, associate director of clinical governance4, Enid Povey, national clinical development manager4, Tim Wreghitt, regional microbiologist5, Nichola Goddard, project manager2, Joanna Ellis, clinical scientist2, Alison Bermingham, clinical scientist2, Praveen Sebastianpillai, data manager2, Angie Lackenby, clinical scientist2, Maria Zambon, director centre for infections2, David Brown, director virus reference department2, Gillian E Smith, regional epidemiologist1, O Noel Gill, head microbiology and epidemiology of STI & HIV department2

1 Health Protection Agency Real-time Syndromic Surveillance Team, Birmingham B3 2PW, 2 Health Protection Agency Centre for Infections, London NW9 5EQ, 3 Health Protection Agency Local and Regional Services, London WC1V 7PP, 4 NHS Direct, Milton Keynes, Buckinghamshire MK14 6DY, 5 Health Protection Agency Regional Microbiology Network, Cambridge CB2 0QW

Correspondence to: A J Elliot alex.elliot{at}hpa.org.uk

Objective To evaluate ascertainment of the onset of community transmission of influenza A/H1N1 2009 (swine flu) in England during the earliest phase of the epidemic through comparing data from two surveillance systems.

Design Cross sectional opportunistic survey.

Study samples Results from self samples by consenting patients who had called the NHS Direct telephone health line with cold or flu symptoms, or both, and results from Health Protection Agency (HPA) regional microbiology laboratories on patients tested according to the clinical algorithm for the management of suspected cases of swine flu.

Setting Six regions of England between 24 May and 30 June 2009.

Main outcome measure Proportion of specimens with laboratory evidence of influenza A/H1N1 2009.

Results Influenza A/H1N1 2009 infections were detected in 91 (7%) of the 1385 self sampled specimens tested. In addition, eight instances of influenza A/H3 infection and two cases of influenza B infection were detected. The weekly rate of change in the proportions of infected individuals according to self obtained samples closely matched the rate of increase in the proportions of infected people reported by HPA regional laboratories. Comparing the data from both systems showed that local community transmission was occurring in London and the West Midlands once HPA regional laboratories began detecting 100 or more influenza A/H1N1 2009 infections, or a proportion positive of over 20% of those tested, each week.

Conclusions Trends in the proportion of patients with influenza A/H1N1 2009 across regions detected through clinical management were mirrored by the proportion of NHS Direct callers with laboratory confirmed infection. The initial concern that information from HPA regional laboratory reports would be too limited because it was based on testing patients with either travel associated risk or who were contacts of other influenza cases was unfounded. Reports from HPA regional laboratories could be used to recognise the extent to which local community transmission was occurring.


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