Thursday, June 01, 2017

Hong Kong's Late Season Flu Surge Continues


Hong Kong's unusual resurgence of severe influenza - which started in early May, several weeks after their regular flu season appeared to have ended - continues to increase in intensity.  As of today, at least 60 severe cases and 35 deaths have been recorded since May 5th. 
The  (modified) chart of severe flu cases in Hong Kong (above) from today's Flu Express shows the wind down from the spring flu season, followed by a short `gap' in April, and then the sudden spike in early May.

On Tuesday, in Hong Kong: A ConFLUence Of Events, we looked at this week's Dragon Boat Festival, and how that might exacerbate this outbreak. In it, Hong Kong's Secretary of Food & Health Dr. Ko Wing-man expressed concerns that the protection from last year's flu shot may be waning, while the new flu shot isn't available yet.

I also listed several recent institutional outbreaks and severe pediatric cases. Over the past two days HK's CHP has added:
CHP investigates case of severe paediatric influenza A infection 

Cluster of Influenza A cases at Shatin Hospital

CHP investigates influenza A outbreak in kindergarten in Sham Shui Po

This late season surge appears to be a mixture of seasonal H3N2, H1N1, and influenza B.  Thus far we've seen nothing to suggest anything unusual about these viruses, and none have shown resistance to antivirals.

Some excepts from today's 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 May 31, 2017)
Reporting period: May 21 – 27, 2017 (Week 21)
  • 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 May 31, 54 severe cases (including 34 deaths) were recorded. Separately, five cases of severe paediatric influenza-associated complication/death (including one death) (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 59 severe cases (including 35 deaths) were recorded cumulatively (as of May 31) (Figure 9). These included:

  • 54 cases (including 34 deaths) among adult patients aged 18 years or above. Among them, 34 patients had infection with influenza A(H3N2), 12 patients with influenza A(H1N1)pdm09, five patients with influenza B and three patients with influenza A with subtype pending. 12 (22.2%) were known to have received the influenza vaccine for the 2016/17 season. Among the 34 fatal cases, 10 (29.4%) were known to have received the influenza vaccine. In the winter season in early 2017, 66 adult severe cases (including 41 deaths) were filed.
  • Five cases (including one death) of severe paediatric influenza-associated complication/ death. All of them did not receive the influenza vaccine for the 2016/17 season. To date in 2017, 13 paediatric cases (including two deaths) were filed.
  • Enhanced surveillance for severe seasonal influenza (Aged 18 years or above)
  • In week 21, 16 cases of influenza associated ICU admission/death were recorded, in which 11 of them were fatal. In the first 4 days of week 22 (May 28 to 31), seven cases of influenza associated ICU admission/death were recorded, in which four of them were fatal.
  • Surveillance of severe paediatric influenza-associated complication/death (Aged below 18 years)
  • In week 21, there was one case of severe paediatric influenza-associated complication. In the first 4 days of week 22 (May 28 to 31), one case of severe paediatric influenza-associated complication was reported.

While exotic viruses like bird flu, Ebola, and Zika grab the headlines, seasonal flu handily beats them all in terms of causing deaths, illnesses and suffering each year.
Seasonal flu viruses are also capable of picking up virulence due to small evolutionary changes (see EID Journal: Emergence of D225G Variant A/H1N1, 2013–14 Flu Season, Florida).

The most famous example, which I described in 2014's When Influenza Goes Rogue,  concerned a new, particularly virulent influenza virus that appeared in Liverpool, England in December of 1950 during the midst of what had been a very mild flu season.

The EID Journal article by  Viboud C, Tam T, Fleming D, Miller MA, Simonsen L. 1951 influenza epidemic, England and Wales, Canada, and the United States, described the impact:

The 1951 influenza epidemic (A/H1N1) caused an unusually high death toll in England; in particular, weekly deaths in Liverpool even surpassed those of the 1918 pandemic. . . . . Why this epidemic was so severe in some areas but not others remains unknown and highlights major gaps in our understanding of interpandemic influenza.

We've no indication of anything unusual about the flu viruses currently circulating in Hong Kong, but history has taught us time and again that influenza is far from a trivial illness, and any unusual activity is worthy of our attention.

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