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Week 52 2012

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Chinese Influenza Weekly Report

(Week 52, December 24– 30, 2012)

(All data are preliminary and may change as more reports are received)

Summary

    In week 52, the influenza activity still remained at low level in south China; the percentage of tests that were positive for influenza and ILI% in north China continued to increased. The north China was in influenza season. Influenza A (H3N2) viruses detected in both south and north China exceeded that of influenza B and pandemic influenza H1N1 2009. However, pandemic influenza H1N1 2009 viruses detected showed an increasing trend.

    Among influenza viruses
antigenically characterized by CNIC since October, 2012, 232 (100%) influenza A (H3N2) viruses are related to A/Victoria/361/2011(H3N2)-like; 84 (96.6%) influenza B/Victoria viruses are related to B/Brisbane/60/2008-like; 7 (100%) influenza B/Yamagata viruses are related to B/Wisconsin/01/2010-like.

    Among influenza viruses tested by CNIC for antiviral resistance since October, 2012, all pandemic influenza H1N1 2009 and influenza A (H3N2) viruses are resistant to adamantine and sensitive to the
neuraminidase inhibitors; all influenza B viruses are sensitive to neuraminidase inhibitors.

 

Outbreak Surveillance

During week 52, no ILI outbreak was reported nationwide.

 

Influenza-like Illness (ILI) Surveillance

During week 52, the percentage of visits with ILI (ILI%) of national sentinel hospitals in south China was 2.4%, which was similar as that of week 51 (2.4%). It was lower the level seen during the same period of the previous year (2.9%).

Figure 1. Percentage of Visits for ILI of Sentinel Hospitals in South China (2010-2013)

During week 52, the ILI% of national sentinel hospitals in north China was 4.2%, which was higher than that of week 51 (3.9%). It was also higher than the level seen during the same period of the previous year (2.8%).

Figure 2. Percentage of Visits for ILI of Sentinel Hospitals in North China (2010-2013)

 

Virologic Surveillance

During week 52, network laboratories tested 2023 specimens, of which 281 (13.9%) were positive for influenza, and influenza A viruses (268, 95.4%) were predominant. During week 52, the percentage of tests that were positive for influenza in south China was 5.1%, which was higher than that in the previous week (4.4%). The percentage of tests that were positive for influenza in north China in the same week was 24.1%, which was higher than that in the previous week (20.9%) (Detailed information of influenza laboratory detections of south and north China is shown as Table 1).

Table 1 Laboratory Detections of ILI Specimens (Week 52, 2012)

 

Week 52

South China

North China

Total

No. of specimens tested

1089

934

2023

No. of positive specimens (%)

56(5.1%)

225(24.1%)

281(13.9%)

Influenza A

46(82.1%)

222(98.7%)

268(95.4%)

 A(H1N1)

0(0)

0(0)

0(0)

A(H3N2)

31(67.4%)

167(75.2%)

198(73.9%)

Pandemic influenza H1N1 2009

7(15.2%)

40(18%)

47(17.5%)

A (subtype not determined)

8(17.4%)

15(6.8%)

23(8.6%)

Influenza B

10(17.9%)

3(1.3%)

13(4.6%)

B (lineage not determined)

10(100%)

3(100%)

13(100%)

Figure 3. Influenza positive tests reported by southern network laboratories (Week 14, 2011 –Week 52, 2012)

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, 2011–Week 52, 2012)

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 week 52, CNIC has antigenically characterized 35 influenza A (H3N2) viruses. All of them are related to A/Victoria/361/2011(H3N2) -like.

During week 52, CNIC has antigenically characterized 23 influenza B/Victoria viruses. 22 (95.7%) of them are related to B/Brisbane/60/2008-like; 1 (4.3%) of them demonstrates reduced titers (8 fold lower in HI titer) with anti-sera produced against B/Brisbane/60/2008.

During week 52, CNIC has antigenically characterized 1 influenza B/Yamagata virus. It was related to B/Wisconsin/01/2010-like.

During October 1– December 30, 2012, CNIC has antigenically characterized 10 pandemic influenza H1N1 2009 viruses. All of them are related to A/California/7/2009-like.

During October 1– December 30, 2012, CNIC has antigenically characterized 232 influenza A (H3N2) viruses. All of them are related to A/Victoria/361/2011(H3N2) -like .

During October 1– December 30, 2012, CNIC has antigenically characterized 87 influenza B/Victoria viruses. 84 (96.6%) are related to B/Brisbane/60/2008-like; 3 (3.4%) demonstrate reduced titers (8 fold lower in HI titer) with anti-sera produced against B/Brisbane/60/2008.

During October 1– December 30, 2012, CNIC has antigenically characterized 7 influenza B/Yamagata viruses. All of them are related to B/Wisconsin/01/2010-like.

 

Antiviral Resistance

During week 52, CNIC has tested 21 influenza A (H3N2) and 9 influenza B viruses for antiviral resistance. All viruses tested are sensitive to the neuraminidase inhibitors.

During October 1– December 30, 2012, among influenza viruses tested by CNIC for antiviral resistance, all pandemic influenza H1N1 2009 and influenza A (H3N2) viruses are resistant to adamantine and sensitive to the neuraminidase inhibitors; all influenza B viruses are sensitive to neuraminidase inhibitors.

 

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