Chinese Influenza Weekly Report

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

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

During week 17 (Apr 20^th 2020 –Apr 26^th 2020), the percentage of outpatient or emergency visits for ILI (ILI%) at national sentinel hospitals in southern provinces was 2.4%, same as the last week (2.4%), lower than the same time of 2017-2019 (3.1%, 3.6% and 4.2%). (Figure 1)

Figure 1. Percentage of Visits for ILI at Sentinel Hospitals in South China

(2017-2021)

During week 17, ILI% at national sentinel hospitals in northern provinces was 1.8%, lower than the last week (1.9%), lower than the same time of 2017-2019 (2.5%, 2.3% and 3.2%). (Figure 2)

Figure 2. Percentage of Visits for ILI at Sentinel Hospitals in North China

(2017-2021)

Virologic Surveillance

During week 17, influenza network laboratories tested 5036 specimens, of which 5(0.1%) were positive for influenza, influenza A and influenza B viruses were 2(40.0%) and 3(60.0%), respectively (Table 1). During week 17, the percentage of specimens that were tested positive for influenza in south China was 0.1%, which was same as the previous week (0.1%)(Figure 3). During week 17, the percentage of specimens that were tested positive for influenza in north China was 0.1%, which was lower than the previous week (0.2%). (Figure 4).

Table 1 Laboratory Detections of ILI Specimens (Week 17, 2020)

Figure 3. Influenza Positive Tests Reported by Southern Network Laboratories (Week 14, 2019–Week 13, 2021)

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, 2019–Week 13, 2021)

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^st, 2019, 785(96.8%) influenza A(H1N1)pdm09 viruses were characterized as A/Brisbane/02/2018-like; 41(3.4%) influenza A(H3N2) viruses were characterized as A/Kansas/14/2017 (EGG)-like, 95(7.9%) influenza A(H3N2) viruses were characterized as A/Kansas/14/2017 (CELL)-like; 160(158%) influenza B/Victoria viruses were characterized as B/Colorado/06/2017-like; 2(100%) influenza B/Yamagata viruses were characterized as B/Phuket/3073/2013-like.

Antiviral Resistance

Since October 1^st, 2019, among the influenza viruses tested by CNIC for antiviral resistance, all influenza A(H1N1)pdm09 and A(H3N2) viruses were resistant to adamantine; All influenza A(H3N2) and B viruses were sensitive to neuraminidase inhibitors. All but 1 influenza A(H1N1)pdm09 were sensitive to neuraminidase inhibitors.

Outbreak Surveillance

During week 17 (Apr 20^th 2020 –Apr 26^th 2020), there was one influenza outbreak event reported nationwide, was negative.

H7N9 Case Report

During week 17, no new human infection with novel reassortant influenza A(H7N9) virus was reported.