Chinese Influenza Weekly Report

(Week 37, September 10 – 16, 2012) 

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

Outbreak Surveillance 

During week 37, no outbreak was reported nationwide. 

Influenza-like Illness (ILI) Surveillance 

During week 37, the percentage of visits with ILI (ILI%) of national sentinel hospitals in south China was 2.6%, which was similar as that of week 36 (2.6%). It was lower than the level seen during the same period of the previous year (2.8%). 

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

During week 37, the ILI% of national sentinel hospitals in north China was 2.8%, which was higher than that of week 36 (2.7%). It was also higher than the level seen during the same period of the previous year (2.3%). 

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

Virologic Surveillance 

During week 37, network laboratories tested 1173 specimens, of which 136 (11.6%) were positive for influenza, and influenza A was predominant. During week 37, the percentage of tests that were positive for influenza in south China was 11.9%, which was lower than that in the previous week (14.2%). The percentage of tests that were positive for influenza in north China in the same week was 10.1%, which was higher than that in the previous week (7.4%) (Detailed information of influenza laboratory detections of south and north China is shown as Table 1). 

Table 1 Laboratory Detections of ILI Specimens (Week 37, 2012) 

Figure 3. Influenza positive tests reported by southern network laboratories (Week 14, 2011 –Week 37, 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 37, 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 37, CNIC has antigenically characterized 32 influenza A (H3N2) viruses. 27 (84.4%) are related to A/Perth/16/2009-like; 5 (15.6%) demonstrate reduced titers (≥8 fold lower in HI titer) with anti-sera produced against A/Perth/16/2009. 

During week 37, CNIC has antigenically characterized 4 influenza B/Yamagata viruses. All of them are related to B/Wisconsin/01/2010-like. 

During October 1, 2011 – September 16, 2012, CNIC has antigenically characterized 50 pandemic influenza H1N1 2009 viruses. 45 (90.0%) are related to A/California/7/2009-like; 5 (10.0%) demonstrate reduced titers (≥8 fold lower in HI titer) with anti-sera produced against A/California/7/2009. 

During October 1, 2011 –September 16, 2012, CNIC has antigenically characterized 2634 influenza A (H3N2) viruses. 2034 (77.2%) are related to A/Perth/16/2009(H3N2)-like; 600 (22.8%) demonstrate reduced titers (≥8 fold lower in HI titer) with anti-sera produced against A/Perth/16/2009(H3N2). 

During October 1, 2011 –September 16, 2012, CNIC has antigenically characterized 3415 influenza B/Victoria viruses. 2535 (74.2%) are related to B/Brisbane/60/2008-like; 880 (25.8%) demonstrate reduced titers (≥8 fold lower in HI titer) with anti-sera produced against B/Brisbane/60/2008. 

During October 1, 2011 –September 16, 2012, CNIC has antigenically characterized 1840 influenza B/Yamagata viruses. 1824 (99.1%) are related to B/Wisconsin/01/2010-like; 16 (0.9%) demonstrate reduced titers (≥8 fold lower in HI titer) with anti-sera produced against B/Wisconsin/01/2010. 

Antiviral Resistance 

During October 1, 2011 – September 16, 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.