HK Flu Express Reports A Modest Post-Holiday Rebound In Flu Cases

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After more than a month of heavy influenza B activity, and the forced early closure of all of Hong Kong's schools a week before the scheduled Lunar New Year Holiday, about two weeks ago we were beginning to see some subtle signs that their winter flu season had peaked.

The wild cards previously mentioned - aside from the innate the unpredictability of flu - were the resumption of school early this week, and the effects of holiday travel and the mixing of people and viruses during the New Year's celebration. 

After two weeks of steep declines in ILI consultations (see chart above), Hong Kong's CHP  today reports a rebound for epi week 8, albeit at levels still below the peaks reported a month ago.

Whether this is just a statistical blip or a trend is something we'll have to wait to see.

Some excerpts from today's HK Flu Express, after which I'll be back with a postscript.

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 Feb 28, 2018)

Reporting period: Feb 18 – 24, 2018 (Week 8)

• The latest surveillance data showed that the local influenza activity remained at a high level in the past few weeks. Currently the predominating virus is influenza B.
• 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 to protect themselves against seasonal influenza and its complications, as well as related hospitalisations and deaths.
• 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)

Laboratory surveillance, 2014-18
 
Among the respiratory specimens received in week 8, the positive percentage of seasonal influenza viruses was 26.07%, which was above the baseline threshold of 10.7% but lower than 27.21% recorded in the previous week (Figure 2). The 2513 influenza viruses detected last week included 414 (4.30%) influenza A(H1), 80 (0.83%) influenza A(H3), 1973 (20.47%) influenza B and 46 (0.48%) influenza C.

(SNIP)

Influenza-like illness outbreak surveillance, 2014-18

In week 8, 16 ILI outbreaks occurring in schools/institutions were recorded (affecting 72 persons), which was lower than 28 outbreaks recorded in the previous week (affecting 151 persons) (Figure 3). In the first 4 days of week 9 (Feb 25-28, 2018), 7 ILI outbreaks in schools/institutions were recorded (affecting 28 persons). Since the start of the 2017/18 winter influenza season in week 2, 488 outbreaks were recorded (as of February 28).

(SNIP)

Surveillance of severe influenza cases

(Note: The data reported are provisional figures and subject to further revision.)
Surveillance for intensive care unit (ICU) admissions/deaths with laboratory confirmation of influenza among adult patients (Aged 18 years or above)

In week 8, 70 adult cases of ICU admission/death with laboratory confirmation of influenza were recorded, in which 51 of them were fatal. 22 of the 70 severe adult cases were known to have received the 2017/18 influenza vaccine. In the first 4 days of week 9 (Feb 25 to 28), 46 cases were recorded, in which 30 of them were fatal.

• Since the start of the 2017/18 winter influenza season in week 2, 443 adult cases of ICU admission/death with laboratory confirmation of influenza were recorded, in which 282 of them were fatal (as of February 28). Among them, 373 patients had infection with influenza B, 37 patients with influenza A(H1N1)pdm09, 23 patients with influenza A(H3N2), three patients with influenza C and seven patients with influenza A pending subtype.
• In comparison, 337, 233 and 109 adult cases were recorded in the same duration of surveillance (seven complete weeks) in the 2014/15 winter, 2015/16 winter and 2017 summer seasons respectively, as compared with 397 cases in the current season (Figure 10, left). The corresponding figures for deaths were 251, 105 and 84 in the above seasons, as compared with 252 deaths in the current season (Figure 10, right).

Global Situation of Influenza Activity

• In Mainland China (week ending Feb 18, 2018), both southern and northern provinces were still in winter influenza season. Although the proportion of ILI cases in emergency and outpatient departments increased as a result of decreased number of patients attending hospitals during the Lunar New Year holiday, the proportion of influenza detections was on a decreasing trend. Currently the influenza activity in southern provinces was higher than that in northern provinces. The proportion of influenza A detection was higher than that of influenza B. Influenza A(H1N1) and influenza B Yamagata viruses are predominating while levels of influenza A(H3N2) and influenza B Victoria viruses remained low. In southern provinces, the proportion of ILI cases in emergency and outpatient departments reported by sentinel hospitals was 5.6%, higher than that reported in the previous week (4.3%) and that in the corresponding period in 2015-2017 (2.7%, 3.0%, 2.7%). In northern provinces, that proportion was 4.5%, higher than those reported in the previous week (3.6%) and the corresponding period in 2015-2017 (2.7%, 3.3%, 2.7%). The proportion of influenza detections in the week ending Feb 18, 2018 was 33.0% (62.7% influenza A and 37.3% influenza B).
• In Macau (as of Feb 27, 2018), the influenza activity has slowed down but remained at high level. The proportions of ILI cases in emergency departments among adults and children decreased. The proportion of influenza detections was 37.6%, lower than 46.7% in the previous week.
• In Taiwan (week ending Feb 24, 2018), influenza activity remained at the peak of the season. In the week ending Feb 24, the proportion of ILI cases in emergency department was 17.16% which was above the threshold of 11.4%. The predominating virus was influenza B.
• In Japan (week ending Feb 18, 2018), the influenza season has started in late November 2017. The average number of reported ILI cases per sentinel site has decreased to 29.65 in the week ending Feb 18, 2018 from 45.38 in the previous week. It was higher than the baseline level of 1.00. The predominating virus in the past five weeks was influenza B, followed by influenza A(H3N2) and A(H1N1)pdm09.

(Continue . . . .)

As mentioned above, and recently in Chinese media, Mainland officials are reporting a late season surge in H1N1 cases over the past few weeks, after a primarily influenza B dominated season.

Whether that tend continues, or carries over to Hong Kong, is something we'll have to watch.

While we can often pick up trends from official Chinese sources, their accounting of seasonal influenza cases and deaths is far from complete, with the NHFPC reporting fewer than 500,000 flu cases, and only 41 deaths, during all of  2017.

Acknowledging a worse flu season this year, in January they reported a sizeable jump to 273949 cases and 56 deaths.

To put that into perspective - Hong Kong (pop. 7 million) - has reported nearly 3 times as many flu-related deaths over the past 6 weeks as Mainland China (pop 1.3 billion) has over the past 13 months.

A sobering reminder of how little we actually know about what is going on with flu in China, along with many other large regions of the world.