GP and school closures over the Christmas period will have affected surveillance indicators so all data should be interpreted with caution. Indeed, several influenza indicators have apparently plateaued. GP consultation rates remain above baseline levels in all four countries. Influenza A H1N1 (2009) and B are the predominant circulating viruses with few, sporadic A (H3N2) viruses detected. The H1N1 (2009) virus strain is virologically and epidemiologically similar to that seen during the pandemic. The virus strains circulating are overall well matched to the current influenza vaccine.
In week 52 (ending 26 December), the weekly influenza/influenza-like illness (ILI) consultation rates decreased in England (98.4 per 100,000) and Scotland (52.0 per 100,000), were stable in Wales (89.2 per 100,000) and increased in Northern Ireland (179.5 per 100,000). The weekly national proportions of NHS Direct calls for cold/flu and fever have decreased in week 52. Thirteen acute respiratory disease outbreaks were reported in UK in week 52, three in primary schools, seven in prisons and two in care homes. This brings the total reported this season so far to 135. It should be noted that most schools across the UK were on holiday in week 52. One-hundred and fourteen of 161 (70.8%) specimens from patients with ILI presenting to sentinel GPs in England in week 52, were reported as positive for influenza. The proportion of specimens reported to DataMart (England) as positive for influenza was 41.4% (2,047 of 4,941). The proportion of samples positive for RSV increased slightly and for rhinovirus continued to decrease. Currently the main circulating influenza strains are influenza A (H1N1) and influenza B. From week 36, 50 deaths associated with influenza infection have been reported. The majority of fatal cases reported were unimmunised. By week 52, the proportion of people in England aged over 65 years who had received the 2010/11 influenza vaccine was 70.0%. For those in a risk group aged under 65 it was 45.4%. In Europe several countries are starting to report influenza activity, primarily associated with influenza A H1N1 (2009). In the USA and Canada overall influenza activity has increased, associated primarily with influenza A (H3N2) and B viruses.
Weekly consultation rates in national sentinel schemes
Due to bank holidays in week 52 (ending 2 January) GP surgeries were only open for three days, which will have impacted GP consultation rates so data should be interpreted cautiously.
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The overall ILI consultation rate from RCGP for England and Wales decreased from 124.4 to 98.4 per 100,000.
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The combined influenza/ILI rate in Northern Ireland has increased from 123.4 (updated rate) to 179.5 per 100,000. This remains above the threshold of 70 per 100,000 (figure 1).
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The Scottish ILI rate decreased from 58.5 to 52 per 100,000 but remains just above the baseline threshold of 50 per 100,000 (figure 1).
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The Welsh influenza rate was stable at 89.2 per 100,000 (compared to 92.2 per 100,000 in week 51) and remains above the baseline threshold of 25 per 100,000 (figure 1).
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Disease severity and mortality data
Excerpts:
Up to 5 January 2011, 50 fatal cases have been verified by HPA as related to influenza infection. Of these cases, 45 have been associated with H1N1 (2009) infection and five with influenza B infection. The deaths have been mainly in younger adults and children, with five cases less than 5 years of age; eight cases from 5 to 14 years; 33 cases from 15 to 64 years and four cases older than 64 years. Thirty-three of 48 fatal cases with available information (69%) were in one of the CMO-defined clinical risk groups for vaccination. The leading reported clinical risk factors were underlying neurological disease (n=11) and respiratory disease including asthma (n=13). Of cases with available information on immunisation history, 36 of 39 cases had not received 2010/11 trivalent influenza vaccine more than two weeks before illness onset. Thirty-three of 34 cases had not received monovalent pandemic influenza vaccination last season.
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