Effectiveness Of Surveillance Systems In Monitoring Swine Flu

Research recently published on bmj.com reports that concerns about the effectiveness of flu surveillance systems during the early phase of the swine flu pandemic were unfounded.

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

In May 2009, laboratory confirmed cases of pandemic influenza A (H1N1) gradually increased in England. There was there was rising concern that existing surveillance systems were failing to recognize 'sustained community transmission.'

As a result, a system of self-sampling which had been piloted during the winter of 2003-2004, was resumed to improve the monitoring of local virus transmission.

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

Among the participants, no one had just returned from an affected country or had had contact with a confirmed case. All were advised to self-treat their symptoms.

There was detection of Pandemic influenza A (H1N1) infections in 97 samples (7 percent). Also, eight influenza A H3 infections and two influenza B infections were found. The peak H1N1 infection rate (20 percent) was in 16 to 24 year olds.

Findings indicated that the variations in the proportion of people infected each week very much matched the rate of increase in clinical laboratory diagnoses. This suggested that there was a reliable indication of the level to which local transmission was occurring in various areas of the country.

For instance, the scheme suggested an absence of sustained community transmission in the regions where clinical diagnoses were low. Furthermore, the scheme provided corresponding and consistent evidence of increasing community transmission compared to reported laboratory diagnoses in regions where clinical diagnoses were expanding quickly.

In closing, the authors remark that if the existing 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 phone clinical advice services should allow reasonable accurate monitoring of the milder flu-like illness attributable to particular flu types in different regions. Also, it should permit measurement of the antiviral susceptibility of strains and any antigenic drift which are random mutations in the genes of a virus that can lead to a loss of immunity.

Following the launch of the National Pandemic Flu Service (NPFS), the Health Protection Agency (HPA) began such a scheme as of 3 August 2009. It deals with callers and internet contacts to the government service. Records from this surveillance system are regularly published in the HPA online weekly epidemiological report on pandemic influenza A (H1N1).