Hong Kong's Late Season Severe Flu Increases For 4th Week

Credit Hong Kong Flu Express Week 22

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Seven weeks ago Hong Kong's CHP announced the apparent end to what had been a relatively mild spring flu season. Three weeks later (May 5th) the CHP Reported A Late Season Flu Surge due to a mixture of H3N2, H1N1 and Influenza B viruses, and reinstated their enhanced surveillance system for severe seasonal influenza.

Since then we've seen the number of influenza-related hospitalizations and deaths, steadily rise.

On May 30th, in Hong Kong: A ConFLUence Of Events, we looked at last week's Dragon Boat Festival, and how that might exacerbate this outbreak. While it is too soon to draw any conclusions on its impact, today's weekly Flu Express Report (WK 22) adds 18 severe flu cases, and 15 deaths to last week's tally. 

Among these are 3 new severe pediatric cases, one of which was fatal.

Essentially, in the past 4 weeks, Hong Kong has more than doubled the number of severe flu cases (n=66), and deaths (n=41), reported during the first four months of 2017.  While Hong Kong often sees a double-peaked flu season, their second (usually smaller) spike generally arrives in late summer.

Thus far we've seen nothing to suggest anything unusual about these viruses, and none have shown resistance to antivirals. In recent weeks Taiwan has reported a similar, albeit less severe, uptick in influenza cases as well. 

Some excepts from today's Flu Express follow.  While technically a Week 22 report, you'll notice - in order to provide the most up-to-date information - they include the first 3 days of week 23 into some of their numbers.

FLU EXPRESS
 
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 7, 2017)

Reporting period: May 28 – June 3, 2017 (Week 22)

• 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 7, 69 severe cases (including 48 deaths) were recorded. Separately, eight 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.

(SNIP)

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 77 severe cases (including 50 deaths) were recorded cumulatively (as of Jun 7) (Figure 9). These included:

• 69 cases (including 48 deaths) among adult patients aged 18 years or above. Among them, 49 patients had infection with influenza A(H3N2), 13 patients with influenza A(H1N1)pdm09, five patients with influenza B and two patients with influenza A without subtype. Seventeen (24.6%) were known to have received the influenza vaccine for the 2016/17 season. Among the 48 fatal cases, 16 (33.3%) were known to have received the influenza vaccine. In the winter season in early 2017, 66 adult severe cases (including 41 deaths) were filed.
• Eight cases (including two deaths) 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, 16 paediatric cases (including three deaths) were filed.

Enhanced surveillance for severe seasonal influenza (Aged 18 years or above)

•  In week 22, 14 cases of influenza associated ICU admission/death were recorded, in which ten of them were fatal. In the first 4 days of week 23 (Jun 4 to 7), eight cases of influenza associated ICU admission/death were recorded, in which seven of them were fatal.

Surveillance of severe paediatric influenza-associated complication/death (Aged below 18 years)

• In week 22, there were four cases of severe paediatric influenza-associated complication/death. In the first 4 days of week 23 (Jun 4 to 7), no cases of severe paediatric influenza-associated complication/death were reported. The case details are as follow:

(Continue . . .)

It isn't clear exactly what is behind this unusual late season surge in severe influenza, but it does remind us that seasonal influenza can vary in virulence from one year to the next, and can sometimes break the rules (see When Influenza Goes Rogue).

We'll be watching the Southern Hemisphere's flu season closely to see if its severity is similarly heightened, and how all this might affect the Northern Hemisphere this fall.