Swine Flu Surveillance Successful

Concerns about the effectiveness of flu surveillance systems during the early phase of the swine flu pandemic were misplaced, according to research published on bmj.com today.

An analysis of samples from members of the public who called NHS Direct with cold or flu-like symptoms during June 2009 closely matched local transmission rates in six regions of England.

As laboratory confirmed cases of pandemic influenza A (H1N1) steadily increased in England during May 2009, there was growing concern that existing surveillance systems were failing to recognise "sustained community transmission".

A scheme of self-sampling, which had been piloted during the winter of 2003-2004, was resumed to enhance the monitoring of local virus transmission.

A total of 1,385 specimens from callers to NHS Direct during June 2009 in six regions of England were tested: two regions where clinical diagnoses were increasing (London and West Midlands) and another four regions that were much less affected.

None of the participants had recently returned from an affected country, or had had contact with a confirmed case and all were advised to self-treat their symptoms.

Pandemic influenza A (H1N1) infections were detected in 97 (7%) samples, in addition to eight influenza A H3 infections and two influenza B infections. The greatest H1N1 infection rate was in 16 to 24 year olds, in whom 20% were infected.

The results show that the change in the proportion of people infected each week closely matched the rate of increase in clinical laboratory diagnoses, giving a reliable indication of the extent to which local transmission was occurring in various parts of the country.

For example, in the regions where clinical diagnoses were low, the scheme suggested an absence of sustained community transmission, whereas in regions where clinical diagnoses were rising rapidly, the scheme provided complementary and reliable evidence of increasing community transmission compared to reported laboratory diagnoses.

The authors conclude that if the current pandemic influenza A (H1N1) intensifies through the coming autumn and winter, self-sampling of members of the public with cold or flu-like symptoms who telephone clinical advice services should enable relatively accurate monitoring of the milder flu-like illness attributable to particular flu types in different regions, as well as both the antiviral susceptibility of strains and any antigenic drift (random mutations in the genes of a virus that can lead to a loss of immunity).

(GK/BMcc)