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Week 26 2011
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Weekly Report
Week 26 2011
Summary In week 26, influenza activity remained at low level in mainland China. The percentage of tests that were positive for influenza virus in south and north China were lower than 3%. Influenza B virus was the predominant strain in both south and north China.In week 26, 6 confirmed cases of pandemic influenza H1N1 2009 were reported in mainland China. No critical or death case was reported. All pandemic influenza H1N1 2009 viruses tested by CNIC since 2011 are resistant to adamantine; only 1 virus is resistant to the neuraminidase inhibitors, others are still sensitive to the neuraminidase inhibitors. All influenza A(H3N2) viruses are resistant to adamantine and sensitive to neuraminidase inhibitors. All influenza B viruses are sensitive to neuraminidase inhibitors. |
Pandemic (H1N1) 2009 Surveillance
During week 26, 6 confirmed cases of pandemic influenza H1N1 2009 were reported from Fujian Province (autonomous region/municipality), which were 6 cases less than that of week 25 (12 cases). In this week, no critical or death case was reported. During January 1 - July 3 2011, 8557 confirmed cases, 243 severe cases (including 118 critical cases) and 70 deaths of pandemic influenza H1N1 2009 have been reported nationwide.
(Note: After cases are reported to the system, the information would be checked by local CDC at all levels to ensure accuracy. From week 3, 2010, data collected in the weekly report refers to the information after examination.)
Outbreak Surveillance
Influenza-like Illness (ILI) Surveillance
During week 26, the percentage of visits with ILI (ILI%) of national sentinel hospitals in south China was 3.5%, which was the same as that of week 25 (3.5%). It was lower than the level seen during the same period of previous years (Figure 1).
Figure 1. Percentage of Visits for ILI of Sentinel Hospitals in South China (2007-2011)
During week 26, the ILI% of national sentinel hospitals in north China was 3.5%, which was slightly higher than that of week 25 (3.3%). It was lower than the level seen during the same period of previous years (Figure 2).
Figure 2. Percentage of Visits for ILI of Sentinel Hospitals in North China (2007-2011)
Virologic Surveillance
During week 26, network laboratories tested 858 specimens, of which 16 (1.9%) were positive for influenza, and influenza B (93.8%) was predominant. During week 26, the percentage of tests that were positive for influenza in south China was 1.8%, which was slightly higher as against that in the previous week (1.6%). During week 26, the percentage of tests that were positive for influenza in north China was 2.1%, which was almost the same as the previous week (2.0%) (Detailed information of influenza laboratory detections of south and north China is shown as Table 1).
Table 1 Laboratory Detections of ILI Specimens (Week 26, 2011)
Week 26 | |||
South China | North China | Total | |
No. of specimens tested | 761 | 97 | 858 |
No. of positive specimens (%) | 14(1.8%) | 2(2.1%) | 16(1.9%) |
Influenza A | 1(7.1%) | 0(0) | 1(6.3%) |
A (H1N1) | 0(0) | 0(0) | 0(0) |
A (H3N2) | 1(100%) | 0(0) | 1(100%) |
A (pandemic influenza H1N1 2009 excluded)[1] | 0(0) | 0(0) | 0(0) |
Pandemic influenza H1N1 2009 | 0(0) | 0(0) | 0(0) |
A (pandemic influenza H1N1 2009 not excluded)[2] | 0(0) | 0(0) | 0(0) |
Influenza B | 13(92.9%) | 2(100%) | 15(93.8%) |
B (lineage not determined) | 13(100%) | 2(100%) | 15(100%) |
Figure 3. Influenza positive tests reported by southern network laboratories (Week 14, 2009 –Week 26, 2011)
Note: Analysis in this part is base on the result of network laboratories. If it is not consistent with the result of NIC, please refer to the result of NIC confirmation.
Figure 4. Influenza positive tests reported by northern network laboratories (Week 14, 2009 –Week 26, 2011)
Note: Analysis in this part is base on the result of network laboratories. If it is not consistent with the result of NIC, please refer to the result of NIC confirmation.
Antigenic Characterization
During January 1 - July 3, 2011, CNIC has antigenically characterized 1456 pandemic influenza H1N1 2009 viruses. 1395 (95.8%) of them are related to A/California/7/2009-like; 61 (4.2%) demonstrate reduced titers (≥8 fold lower in HI titer) with anti-sera produced against A/California/7/2009.
During January 1 - July 3, 2011, CNIC has antigenically characterized 14 influenza A(H1N1) viruses. 12 (85.7%) are related to A/Brisbane/59/2007(H1N1)-like; 2 (14.3%) demonstrate reduced titers (≥8 fold lower in HI titer) with anti-sera produced against A/Brisbane/59/2007(H1N1).
During January 1 - July 3, 2011, CNIC has antigenically characterized 117 influenza A(H3N2) viruses. 113 (96.6%) are related to A/Perth/16/2009(H3N2)-like; 4 (3.4%) demonstrate reduced titers (≥8 fold lower in HI titer) with anti-sera produced against A/Perth/16/2009(H3N2).
During January 1 - July 3, 2011, CNIC has antigenically characterized 592 influenza B/Victoria viruses. 542 (91.6%) are related to B/Brisbane/60/2008-like; 50 (8.4%) demonstrate reduced titers (≥8 fold lower in HI titer) with anti-sera produced against B/Brisbane/60/2008.
During January 1 - July 3, 2011, CNIC has antigenically characterized 592 influenza B/Victoria viruses. 542 (91.6%) are related to B/Brisbane/60/2008-like; 50 (8.4%) demonstrate reduced titers (≥8 fold lower in HI titer) with anti-sera produced against B/Brisbane/60/2008.
During January 1, 2010 - July 3, 2011, CNIC has antigenically characterized 647 influenza B/Yamagata viruses. 374 (57.8%) are related to B/Florida/4/2006-like; 273 (42.2%) demonstrate reduced titers (≥8 fold lower in HI titer) with anti-sera produced against B/Florida/4/2006.
During January 1 - July 3, 2011, CNIC has sequenced 47 pandemic influenza H1N1 2009 viruses. All the viruses have high homology (＞98%) with the A/California/7/2009(H1N1) reference virus selected by WHO and the A/Sichuan/SWL1/2009 reference virus in mainland China. Only 1 virus possesses mutation at the NA gene at amino acid position 274 and is resistant to the neuraminidase inhibitors. The significance of mutations at other amino acid positions is still unclear.
Antiviral Resistance
During January 1 - July 3, 2011, all pandemic influenza H1N1 2009 viruses tested by CNIC are resistant to adamantine; only 1 virus is resistant to the neuraminidase inhibitors, others are still sensitive to the neuraminidase inhibitors. All influenza A(H3N2) viruses are resistant to adamantine and sensitive to neuraminidase inhibitors. All influenza B viruses are sensitive to neuraminidase inhibitors. 
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