Press Release

Latest update on surveillance data in winter influenza season

25 March 2015

The Centre for Health Protection (CHP) of the Department of Health today (March 25) reported the latest surveillance data of the winter influenza season, and again urged the public to heighten vigilance and get vaccinated early against seasonal influenza.

"Although the latest surveillance data show that the overall influenza activity continued to decrease, it is still above the baseline. We expect that the local influenza activity will remain above the baseline for some time," a spokesman for the CHP said.

Laboratory surveillance

The percentage positive for seasonal influenza viruses decreased from 18.0 per cent in the second week of March to 14.8 per cent last week, which is lower than 15.4 per cent (arrival of season) in the first week of 2015, among respiratory specimens received by the CHP's Public Health Laboratory Services Branch.

Among influenza virus detections, 82.1 per cent were A(H3N2) while 14.7 per cent were B.

Severe cases

From noon yesterday (March 24) to noon today, seven additional cases of influenza-associated admission to intensive care units or death (including five deaths) among adults aged 18 or above had been recorded under the enhanced surveillance in collaboration with public and private hospitals reactivated since January 2, bringing the total to 565 (424 deaths) so far. Among them, 533 were A(H3N2), eight were A(H1N1)pdm09, seven were A pending subtype and 17 were B. In the last winter season in early 2014, 266 cases (133 deaths) were filed.

Last week (from March 15 to 21), 38 cases (25 deaths) were recorded. Separately, a daily average of five cases (three deaths) were filed in the last seven days (from March 18 to 24), compared with 6.9 cases (5.4 deaths) in the preceding seven days (from March 11 to 17).

Meanwhile, no additional cases of severe paediatric influenza-associated complication or death among children aged under 18 have been reported since yesterday via the ongoing reporting system and the total this year hence remains at 18 (one death) and all were A(H3N2). In 2014, 27 cases (four deaths) were filed.

Institutional outbreaks

Turning to influenza-like illness (ILI), four institutional outbreaks (affecting 19 persons) were reported to the CHP yesterday (March 24) by a residential care home for the elderly (one outbreak, three persons) and schools (three outbreaks, 16 persons).

The weekly number of outbreaks decreased from 22 (affecting 93 persons) in the second week of March to 19 (75 persons) last week. As of yesterday, nine (45 persons) had been recorded so far this week. Outbreaks in the past four weeks mainly occurred in residential care homes for the elderly (71.8 per cent) and schools (19.2 per cent).

Vaccination

As of March 22, about 256 000 doses and 247 000 doses of influenza vaccines had been administered to eligible groups under the Government Vaccination Programme and the Vaccination Subsidy Schemes 2014/15 respectively, representing 8 per cent and 5 per cent increases from the same period of last year.

Neighbouring and overseas areas

The influenza activity in a number of overseas areas in the northern hemisphere has peaked and has been decreasing while that of the others remain elevated, with A(H3N2) virus predominating so far.

In the United States, influenza activity is still elevated but continues to decrease. The percentage tested positive for influenza viruses in the United States peaked at 31.79 per cent in the last week of 2014 and gradually dropped to 11.2 per cent in the week ending March 14. While H3N2 viruses have been most common this season, influenza B viruses accounted for the largest proportion of circulating viruses in recent weeks. In Canada, the percentage tested positive for influenza A virus has continued to decline to 6.6 per cent in the week ending March 14 from 8.6 per cent in the previous week. The percentage of positive influenza B tests continued to increase and was 10.0 per cent in the week ending March 14.

In Europe, following a consistently high proportion of influenza virus detections of 50 per cent or higher in sentinel specimens since the week ending January 25, the positivity rate decreased to 41 per cent in the week ending March 15. The percentage tested positive for influenza viruses in England already reached a peak of 31.7 per cent in the first week of 2015 and decreased to 12.2 per cent in the week ending March 15. Indicators of influenza activity generally were at similar levels compared to the previous week, although influenza B activity appears to be increasing.

Regarding our neighbouring regions, Taiwan is still in the influenza season and surveillance data showed that the percentage tested positive for influenza viruses in the week ending March 7 remained at a high level of 29.4 per cent. In Japan, the average number of reported ILI cases per sentinel site further decreased to 3.99 in the week ending March 15 from 4.32 in the preceding week.

The public should maintain good personal and environmental hygiene against influenza and other respiratory illnesses:

• Receive seasonal influenza vaccination for personal protection;
• Wash hands with liquid soap and water properly whenever possibly contaminated;
• When hands are not visibly soiled, clean them with 70 to 80 per cent alcohol-based handrub;
• Wash or clean hands frequently, especially before touching the mouth, nose or eyes, or after touching public installations such as handrails or door knobs;
• Cover the nose and mouth when sneezing or coughing, and wash hands thoroughly afterwards;
• Dispose of soiled tissue paper properly in a lidded rubbish bin;
• Put on a surgical mask when respiratory symptoms develop;
• Maintain good indoor ventilation;
• When influenza is prevalent, avoid going to crowded or poorly ventilated public places; high-risk individuals may consider putting on surgical masks when staying in such places; and
• Maintain a balanced diet, exercise regularly, take adequate rest, do not smoke and avoid overstress.

The public may visit the CHP's pages below for more information:

• The influenza page ( www.chp.gov.hk/en/view_content/14843.html );
• The weekly Flu Express report ( www.chp.gov.hk/en/view_content/2108.html );
• The update on severe seasonal influenza cases ( www.chp.gov.hk/files/pdf/flu_update_en.pdf );
• The vaccination schemes page ( www.chp.gov.hk/en/view_content/17980.html );
• The list of participating doctors ( www.chp.gov.hk/en/view_content/34664.html );
• The Facebook Page ( www.fb.com/CentreforHealthProtection ); and
• The YouTube Channel ( www.youtube.com/c/ChpGovHkChannel ).