Thursday, June 29, 2017

Hong Kong's Late Season Flu Surge Continues To Increase


Hong Kong's flu season - declared over in mid-April - sprung back to life in early May and over the past 7 weeks has produced more flu-related severe illness and death than either of the last two seasonal outbreaks (fall 2016 & spring 2017).  
While Hong Kong often sees a second yearly flu season, it usually arrives in late July or August - not in early May - and it is usually milder than the spring season (see chart above).
During the first wave of 2017, which ran from February through April, Hong Kong reported  74 severe cases (including 42 deaths). So far in this second wave (starting May 5th), Hong Kong has reported 143 severe cases (including 102 deaths).
While the timing is unusual, and the severity elevated, this second wave pales in comparison to 2016's spring (primary) flu season, which saw nearly 440 severe cases, and more than 200 deaths (cite Flu Express wk 21 2016).
This late season surge is reportedly a mixture of seasonal H3N2, H1N1, and influenza B.  Thus far we've seen nothing to suggest anything unusual about these viruses - beyond the timing and high number of severe cases - and none have shown resistance to antivirals.

While we are always concerned over the emergence of a pandemic strain, seasonal flu kills hundreds of thousands of people every year, and from time to time can ramp up its virulence to near-pandemic intensity (see When Influenza Goes Rogue).
So any deviation from the norm is worthy of our attention. 
First some excerpts from today's Flu Express, then I'll be back with a bit more.

VOLUME 14, NUMBER 25 (PUBLISHED ON Jun 29, 2017)


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 Jun 28, 2017)

Reporting period: Jun 18 – 24, 2017 (Week 25)

  • The latest surveillance data showed that the local influenza activity continued to increase.
  • 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 Jun 28, 133 severe cases (including 100 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 143 severe cases (including 102 deaths) were recorded cumulatively (as of Jun 28) (Figure 9). These included:

  • 133 cases (including 100 deaths) among adult patients aged 18 years or above. Among them, 104 patients had infection with influenza A(H3N2), 16 patients with influenza A(H1N1)pdm09, seven patients with influenza B and six patients with influenza A pending subtype. Forty-two (31.6%) were known to have received the influenza vaccine for the 2016/17 season. Among the 100 fatal cases, 39 (39.0%) 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 25, 21 cases of influenza associated ICU admission/death were recorded, in which 16 of them were fatal. In the first 4 days of week 26 (Jun 25 to 28), 18 cases of influenza associated ICU admission/death were recorded, in which 13 of them were fatal.
Surveillance of severe paediatric influenza-associated complication/death (Aged below 18 years)
  • In week 25 and the first 4 days of week 26 (Jun 25 to 28), there were no cases of severe paediatric influenza-associated complication/ death.
 (Continue . . . )

Elsewhere around the world, we aren't hearing a lot about seasonal influenza, with most countries reporting to be at or near their inter-seasonal norms. The WHO's most recent seasonal influenza report (#292) states:
In the temperate zone of the southern hemisphere, influenza activity continued to increase and was above seasonal threshold levels in South America but remained low in general in Oceania. Influenza activity in the temperate zone of the northern hemisphere continued to decrease. Worldwide, influenza A(H3N2) and B viruses co-circulated.
One notable exception is Taiwan, which continues to report surge in influenza over the past few weeks (see graph below), although reportedly not as severe as Hong Kong's.

Overnight Australian media is reporting a spike in flu cases in New South Wales (see Flu season in New South Wales tracked to be worst on record) although the level of flu reported across the rest of Australia appears near average for this time of year.

While it isn't necessarily a harbinger of what the Northern Hemisphere can expect next fall, we'll continue to keep a close eye on the Southern Hemisphere's flu season as it progresses over the next few months.

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