Chinese Influenza Weekly Report

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

Outbreak Surveillance 

During week 13(March 28- April 3, 2016), there was 98 outbreaks reported nationwide, 69 of them were B, 10 of them were A(H1N1)pdm09, 1 of them was A(H3N2), 1 of them were negative , 11 of them were mixed, and 6 of them were untyped. 

Surveillance of outpatient or emergency visits for Influenza-like Illness (ILI) 

During week 13, the percentage of outpatient or emergency visits for ILI (ILI %) at national sentinel hospitals in south China was 4.0% , lower than last week 4.1%, higher than the same week of 2014 and 2015（3.1% and 2.8%）. (Figure 1) 

Figure 1. Percentage of Visits for ILI at Sentinel Hospitals in South China (2011-2016) 

During week 13, ILI% at national sentinel hospitals in north China was 3.7%, lower than last week 4.0%, higher than the same week of 2014 and 2015（2.9% and 2.6%）. (Figure 2) 

Figure 2. Percentage of Visits for ILI at Sentinel Hospitals in North China (2011-2016) 

  Virologic Surveillance 

During week 13, influenza network laboratories tested 6110 specimens, of which 1880 （30.8%）) were positive for influenza, influenza A and influenza B virus were 423 （22.5%）and 1457（77.5%），respectively(Table 1). During week 13, the percentage of specimens that were tested positive for influenza in south China was 31.5%, which was lower than the previous week （35.0%）(Figure 3).During week 13, the percentage of specimens that were tested positive for influenza in north China was 29.8%, which was lower than the previous week（38.0%）(Figure 4). 

 

Figure 3. Influenza Positive Tests Reported by Southern Network Laboratories (Week 14, 2014–Week 13, 2016)

Note: Analysis in this part was based on the test results of network laboratories. If it were not consistent with the results of CNIC confirmation, the results of CNIC confirmation were used.

Figure 4. Influenza Positive Tests Reported by Northern Network Laboratories (Week 14, 2014–Week 13, 2016)

Note: Analysis in this part was based on the result of network laboratories. If it were not consistent with the results of CNIC confirmation, the results of CNIC confirmation were used. 

Antigenic Characterization 

Since October 1^nd, 2015, 267（94.3%） of the 283 A(H1N1)pdm09 viruses tested were characterized as A/California/7/2009-like; 47（29.2%） of the 161 A(H3N2) influenza viruses tested were characterized as A/Switzerland/9715293/2013 (H3N2)(EGG)-like, 125（77.6%） of the 161 A(H3N2)influenza viruses tested were characterized as A/Switzerland/9715293/2013 (H3N2)(CELL)-like; 342（99.1%） of the 345 influenza B/Yamagata lineage viruses tested were characterized asB/Phuket/3073/2013-like; 142（53.2%） of the 267 influenza B/Victoria lineage viruses tested have been characterized as B/Brisbane/60/2008-like. 

Antiviral Resistance 

Since October 1^nd, 2015, among the influenza viruses tested by CNIC for antiviral resistance, all influenza A(H1N1)pdm09 and all influenza A(H3N2) viruses were resistant to adamantine ; all influenza A(H1N1) pdm09 、A(H3N2) and B viruses were sensitive to neuraminidase inhibitors.