Emerging disease surveillance and response

Influenza Situation Update

1 April 2014

Summary

In the Northern Hemisphere countries, influenza-like illness (ILI) activity was variable however ILI activity appears to be decreasing. In northern China, during the week 17 to 23 March 2014, the percentage of visits for ILI (ILI%) at national sentinel hospitals established in 2009 in north China was 3.0%, which was the same as that of the previous week and the same week of 2012, but higher than the same weeks in 2013 (2.6%). The proportion of ILI specimens positive for influenza, however, has decreased: 230 of 1748 (13.2%) ILI specimens were positive for influenza. Of the positive specimens, 48 (20.9%) were influenza A (29 were H3N2 and 19 were (H1N1)pdm09) and 182 (79.1%) were influenza B(2 Yamagata and 180 lineage not determined). In Mongolia, during the week 17 to 23 March 2014, ILI activity based on the proportion of outpatients exhibiting ILI was above the upper tolerance limit (60%), however, substantially lower than the proportion observed 2 weeks ago. The proportion of patients with pneumonia among the hospitalized was also lower than the proportion observed 2 weeks ago. The proportion of ILI specimens positive for influenza also decreased; there were 74 specimens positive for influenza virus among 240 ILI samples (30.8%) submitted: of those laboratory confirmed, 14 were influenza A(H1N1)pdm09, 26 were influenza A(H3) and 34 influenza B (lineage not determined) during 23 February to 1 March 2014. In Japan, during the week 20 to 26 March 2014, ILI activity decreased; the number of ILI cases per sentinel reporting site was 18.6, lower than the previous week and further decreased from the peak in February. Similarly in the Republic of Korea, for the week ending 22 March 2014, ILI activity decreased; the number of ILI cases was 26.8 per 1000 patients at sentinel sites, lower than the previous week. Proportion of ILI specimens positive for influenza also decreased; there were 115 specimens positive for influenza virus among 240 (47.9%) ILI samples submitted: 36 influenza A(H3), 5 influenza A(H1N1)pdm09 and 74 influenza B (lineage not determined) during 16 to 22 March 2014.

In the subtropics/tropics, overall ILI activity remained variable. In Southern China, during the week 17 to 23 March 2014, the ILI at national sentinel hospitals established in 2009 in south China was 3.0%, which was higher than that of the previous week (2.9%). ILI activity was lower than that for the same week of 2012 (3.2%) but higher than the same week of 2013 (2.5%). The proportion of ILI specimens positive for influenza has decreased: 490 of 2924 (16.8%) ILI specimens were positive for influenza. Of the positive specimens, 198 (40.4%) were influenza A (53 were H3N2, 143 were (H1N1)pdm09 and 2 subtype not determined) and 292 (59.6%) were influenza B(lineage not determined). In Hong Kong (China), during 16 to 22 March 2014, local influenza activity has been gradually decreasing since early March though activity of influenza B remained at a relatively high level. Of the 470 samples positive for influenza during this week, 60 were influenza A(H3), 297 influenza B, 110 influenza A(H1N1)pdm09, and 3 influenza C viruses. During 16 to 22 March 2014, hospital admission rates with principal diagnosis of influenza decreased or remained stable for children aged 0-4 years, persons aged 5-64 years and persons aged 65 years and above (1.50, 0.12 and 0.50 case, respectively) per 10 000 people in the age group. Weekly number of deaths with any diagnosis of influenza in public hospitals has decreased.

In the Mekong, influenza activity decreased. In Lao PDR, during 16 to 22 March 2014, 6 of 50 (12.0%) ILI specimens were positive for influenza: 3 were influenza A(H1N1)pdm09and 3 were influenza B (Lineage not determined). In Viet Nam, during 2 to 8 March 2014, 19 of 56 (33.9%) ILI specimens were positive for influenza: 9 were influenza A(H1N1)pdm09, 2 was influenza A(H3) and 8 were influenza B (Lineage not determined).

In Singapore, acute respiratory infection (ARI*) activity decreased. During 16 to 22 March 2014, 2,003 patients sought treatment compared to 2,493 patients the previous week. The proportion of cases with ILI among the polyclinic ARI cases remained low at below 1%. Of 99 ILI samples collected in the past 4 weeks in the community, 30.3% were positive for influenza virus. Of all the influenza virus isolates in February 2014, 15.0% were influenza A(H3N2), 35.0% were influenza A(H1N1)pdm09 and 48.3% were influenza B.

In Australia, ILI activity decreased compared to the previous two weeks. During the week 16 to 22 Mar 2014, 12 of 201 (6.0%) ILI specimens tested positive for influenza: 1 was influenza A(H3), 6 were influenza A(H1N1)pdm09 and 5 were influenza B (lineage not determined).

In the Pacific Islands, ILI activity was variable with an increase observed in a number of islands. During the week ending 23 March 2014, none of the Pacific Islands reported weekly ILI case numbers above the threshold of 90% of their historical values.


Global influenza situation

Epidemiological update:
http://www.who.int/influenza/surveillance_monitoring/updates/latest_update_GIP_surveillance/

Virological update:
http://www.who.int/influenza/gisrs_laboratory/updates/summaryreport


*ARI defined as clinical diagnosis of acute upper respiratory tract infection (ICD9 460 – 465: Acute Nosopharyngitis (common cold); 461 Acute Sinusitis; 462 Acute Pharyngitis; 463 Acute Tonsillitis; 464 Acute Laryngitis and Tracheitis; 465 Acute Upper Respiratory Infections of Multiple or Unspecified Sites; 466 Acute Bronchitis and Bronchiolitis). ILI defined as temperature >38C with cough or sore throat.


For further information on the influenza situation or its surveillance, please visit the following links:


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