Thursday, July 06, 2017

Hong Kong's Summer Flu Surge Enters 9th Week


In early May, several weeks after Hong Kong's winter flu season appeared to have ended, severe cases of influenza began showing up in local hospitals (see Hong Kong CHP Reports A Late Season Flu Surge), forcing the Centre for Health Protection to reinstate their enhanced surveillance for severe seasonal influenza system.
While Hong Kong is known for having a biphasic or `double peaked’  flu season, with their heaviest activity usually from February–April and (a less severe) season in mid-to-late summer (cite), the timing and severity of this surge is unexpected.
Since sounding the alarm 60 days ago, the number of severe cases (and deaths) has steadily climbed, far exceeding anything reported during the regular 2017 flu season.
Whereas Hong Kong's initial influenza season of 2017 - which ran from February through April - produced 74 severe cases and 42 deaths, so far in this second wave has generated 176 severe cases and 120 deaths.
Despite a high percentage of deaths (68%) among reported severe cases, laboratory surveillance in this week's Flu Express continues to show that Hong Kong is dealing with a mixture of seasonal flu viruses (H3N2, H1N1 & Influenza B) with H3N2 dominating. 
Laboratory surveillance, 2013-17
Among the respiratory specimens received in week 26, 1536 (31.46%) were tested positive for seasonal influenza viruses, including 79 (1.62%) influenza A(H1), 1413 (28.94%) influenza A(H3), 34 (0.70%) influenza B and 10 (0.20%) influenza C. The percentage of respiratory specimens tested positive for seasonal influenza viruses last week was 31.46%, which was higher than 20.76% recorded in the previous week (Figure 2). Among the influenza viruses detected in the last week, the proportions of A(H3), A(H1), B and C were 92.0%, 5.1%, 2.2% and 0.7% respectively.
The 31.46% influenza positive rate among respiratory samples tested is a 50% jump over last week, and is the sharpest peak reported since January-February of 2015 (see chart below). While elevated, the number deaths in this wave pale in comparison to the nearly 500 fatalities reported during that 2015 season.

Taiwan is reporting an elevated, but less severe, summer flu season (see A Look At Taiwan's Out Of Season Flu Surge), and recent reports suggest both Australia and New Zealand are entering their flu seasons. H3N2 continues to be the most reported Influenza A subtype this summer.
H3N2 flu seasons often prove more severe than H1N1 - particularly among the elderly - and in recent years the VE (Vaccine Effectiveness) of the flu vaccine has suffered due to a growing genetic diversity among circulating H3N2 viruses (see Eurosurveillance: Interim Estimates Of Flu Vaccine Effectiveness Against A(H3N2) - Canada, January 2017).
All reasons why we will continue to follow influenza's unusual activity in Hong Kong, and its general behavior in the southern hemisphere this summer, closely.  Some excerpts from this week's Hong Kong Flu Express follow:

Flu Express is a weekly report produced by the Respiratory Disease Office of the Centre for Health Protection. It monitors and summarizes the latest local and global influenza activities.
Local Situation of Influenza Activity (as of Jul 5, 2017)
Reporting period: Jun 25 – Jul 1, 2017 (Week 26)
  • The latest surveillance data showed that the local influenza activity has further increased and reached a high level.
  • The Centre for Health Protection (CHP) has collaborated with the Hospital Authority (HA) and private hospitals to reactivate the enhanced surveillance for severe seasonal influenza cases (i.e. influenza-associated admissions to intensive care unit or deaths) among patients aged 18 or above since May 5, 2017. As of Jul 5, 166 severe cases (including 118 deaths) were recorded. Separately, ten cases of severe paediatric influenza-associated complication/death (including two deaths) (aged below 18 years) were recorded in the same period.
  • Apart from adopting personal, hand and environmental hygiene practices against respiratory illnesses, those members of the public who have not received influenza vaccine are urged to get vaccinated as soon as possible for personal protection.
  • Influenza can cause serious illnesses in high-risk individuals and even healthy persons. Given that seasonal influenza vaccines are safe and effective, all persons aged 6 months or above except those with known contraindications are recommended to receive influenza vaccine for personal protection.

Surveillance of severe influenza cases
(Note: The data reported are provisional figures and subject to further revision)
Since the activation of the enhanced surveillance for severe influenza infection on May 5, 2017, a total of 176 severe cases (including 120 deaths) were recorded cumulatively (as of Jul 5) (Figure 9). These included:
  • 166 cases (including 118 deaths) among adult patients aged 18 years or above. Among them, 134 patients had infection with influenza A(H3N2), 18 patients with influenza A(H1N1)pdm09, eight patients with influenza B and six patients with influenza A pending subtype. Fifty-four (32.5%) were known to have received the influenza vaccine for the 2016/17 season. Among the 118 fatal cases, 47 (39.8%) were known to have received the influenza vaccine. In the winter season in early 2017, 66 adult severe cases (including 41 deaths) were filed.
  • Ten cases (including two deaths) of severe paediatric influenza-associated complication/ death. Nine (90.0%) cases did not receive the influenza vaccine for the 2016/17 season. To date in 2017, 18 paediatric cases (including three deaths) were filed.
Enhanced surveillance for severe seasonal influenza (Aged 18 years or above)
  • In week 26, 33 cases of influenza associated ICU admission/death were recorded (including 24 deaths), which was higher than 21 cases (including 17 deaths) recorded in week 25. In the first 4 days of week 27 (Jul 2 to 5), 18 cases of influenza associated ICU admission/death were recorded, in which 6 of them were fatal.
Surveillance of severe paediatric influenza-associated complication/death (Aged below 18 years)
  • In week 26 and the first 4 days of week 27 (Jul 2 to 5), there were no cases of severe paediatric influenza-associated complication/ death.
        (Continue . .  )

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