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.
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.


METHODS
Cross sectional opportunistic survey.


METHODS
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.


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


METHODS
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.
Elliot
Alex J
AJ
Health Protection Agency Real-time Syndromic Surveillance Team, Birmingham B3 2PW. alex.elliot@hpa.org.uk
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Cassandra
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Alicia
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Caterina
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Ian
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D000293:Adolescent; D000328:Adult; D000368:Aged; D017714:Community-Acquired Infections / Q000453:epidemiology / Q000635:transmission; D003430:Cross-Sectional Studies; D004739:England / Q000453:epidemiology; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology / Q000635:transmission*; D008875:Middle Aged; D013689:Telephone; D055815:Young Adult