Avian Flu Diary: HK Flu Express Wk 29: Influenza Activity Remains At A Very High Level

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Fourteen weeks ago Hong Kong's CHP declared the end of last winter's mild flu epidemic, with their Flu Express Week 15 reporting a `low level' of flu activity by mid-April. Two weeks later, quite unexpectedly, the Hong Kong CHP Reported A Late Season Flu Surge, and reinstated their enhanced surveillance for severe seasonal influenza.

Since then we've seen a nearly continuous rise in severe seasonal flu cases - mostly H3N2 - which has claimed more than two hundred lives, and has severely impacted Hong Kong's hospital system.

While Hong Kong is known for having a biphasic or `double peaked’ flu season, their heaviest activity usually occurs from February–April with a less severe season in mid to late summer (see Seasonality of Influenza A(H3N2) Virus: A Hong Kong Perspective (1997–2006).

This summer's flu epidemic has lasted longer, and has been far more severe, than their last two flu epidemics (see chart at top of blog), and shows no signs of abatement. According to the latest Hospital Authority Hospital Key Statistics daily report, inpatient occupancy rates range from 96% to 124% across 17 local hospitals.

Since last week an additional 67 severe cases, and 47 deaths, have been recorded due to flu-related illness. With 255 deaths since May 5th, this summer's flu outbreak has claimed 6 times the number of lives caused by Hong Kong's 2017's winter flu (n=41).

Although a few indicators have slowed slightly over the past week, it is too soon to say whether Hong Kong has reached the peak of their epidemic. The CHP warns to expect a `high level' of flu activity over the coming weeks.

Some excerpts from today's Flu Express report, and the I'll return with a bit more.

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 Jul 26, 2017)
Reporting period: Jul 16 – 22, 2017 (Week 29)

The latest surveillance data showed that the local influenza activity remained at a very high level in the past week. It is foreseen that the influenza activity will remain at a very high level in the coming weeks.

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 26, 361 severe cases (including 252 deaths) were recorded. Separately, 18 cases of severe paediatric influenza-associated complication/death (including three 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 may get the vaccination 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 379 severe cases (including 255 deaths) were recorded cumulatively (as of Jul 26) (Figure 9). These included:

361 cases (including 252 deaths) among adult patients aged 18 years or above. Among them, 316 patients had infection with influenza A(H3N2), 21 patients with influenza A(H1N1)pdm09, 13 patients with influenza B and 11 patients with influenza A pending subtype. 131 (36.3%) were known to have received the influenza vaccine for the 2016/17 season. Among the 252 fatal cases, 113 (44.8%) were known to have received the influenza vaccine. In the winter season in early 2017, 66 adult severe cases (including 41 deaths) were filed.

18 cases (including three deaths) of severe paediatric influenza-associated complication/ death. Sixteen (88.9%) cases did not receive the influenza vaccine for the 2016/17 season. To date in 2017, 26 paediatric cases (including four deaths) were filed.

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

In week 29, 65 cases of influenza associated ICU admission/death were recorded (including 39 deaths), which was lower than 72 cases (including 52 deaths) recorded in week 28. In the first 4 days of week 30 (Jul 23 to 26), 37 cases of influenza associated ICU admission/death were recorded, in which 29 of them were fatal.
Surveillance of severe paediatric influenza-associated complication/death (Aged below 18 years)

 In week 29, four cases of severe paediatric influenza-associated complication were reported. In the first 4 days of week 30 (Jul 23 to 26), one case of severe paediatric influenza-associated complication was reported. The case details are as follow:

http://www.chp.gov.hk/files/pdf/fluexpress_web_week29_27_7_2017_eng.pdf

(Continue . . .)

We have been following similar, albeit less severe, reports from other regions of eastern Asia (see Taiwan's Summer H3N2 Epidemic Continues Near Peak and Macao, Hong Kong & Guangdong Province All Reporting Heavy Flu Activity) in recent weeks.

Getting good numbers out of Mainland China is difficult, but Sharon Sanders of Flutrackers has been monitoring media reports in their China Seasonal Flu Tracking forum and has posted the following threads in the past few days.

China - Pediatric flu patients up significantly in July in Heyuan, Guangdong province - July 27, 2017

China - Recent high incidence of flu patient overcrowding in Hengfeng, Jiangxi Province - July 26, 2017

China - Major hospitals in Dongguan reporting overcrowding due to flu patients - up 20-30% in July - Guangdong province - July 21, 2017

The cause of this year's out-of-season heavy flu activity remains unclear, although several theories have been advanced, including waning late-season effectiveness of last year's flu vaccine, and a possible antigenic change in the H3N2 virus.

For more on those possibilities, you may want to revisit these recent blogs: