HK CHP Avian Influenza Report: Week 5

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Hong Kong's Centre For Health Protection has published their Weekly Avian Influenza Report, and while it ostensibly contains the previous week's cases, the reality is the vast majority of the 63 cases listed in this week's edition occurred in January and were previously reported by the CHP last Friday (see HK CHP Notified of Another 57 H7N9 Cases).

That said, today's report does provide us with additional, albeit incomplete details on the age, gender, and condition of many of those cases.

As we discussed over the weekend in The Skies Aren't They Only Thing Hazy In China, data from the Mainland on this year's avian flu epidemic has become increasingly fragmented and delayed, and our ability to track the size and scope of this 5th wave of H7N9 cases has been severely hampered.

Since we rarely get to work with the data we want, we'll do the best we can with data we have.  Some excerpts from today's report, after which I'll have a bit more. 

Avian Influenza Report
 
Avian Influenza Report is a weekly report produced by the Respiratory Disease Office, Centre for Health Protection of the Department of Health. This report highlights global avian influenza activity in humans and birds.

VOLUME 13, NUMBER 05
Reporting period: January 29, 2017 – February 4, 2017 (Week 05)

(Published on February 7, 2017)

Summary

1. Since the previous issue of Avian Influenza Report (AIR), there were 63 new human cases of avian influenza A(H7N9) reported by Mainland China health authorities in Jiangsu (13 cases), Guangdong (10 cases), Hunan (9 cases), Zhejiang (8 cases), Jiangxi (7 cases), Anhui (5 cases), Fujian (5 cases) , Hubei (4 cases), Guangxi (1 case) and Sichuan (1 case). In addition, health authority in Taiwan reported one imported human case of avian influenza A(H7N9). Since March 2013 (as of February 6, 2017), there were a total of 1107 human cases of avian influenza A(H7N9) reported globally. Since November 2016 (as of February 6, 2017), 302 cases have been recorded in Mainland China.
2. Since the previous issue of AIR, there were no new human cases of avian influenza A(H5N6). Since 2014 (as of February 4, 2017), 16 human cases of avian influenza A(H5N6) were reported globally and all occurred in Mainland China. The latest case was reported on December 1, 2016.
3. There were no new human cases of avian influenza A(H5N1) reported by the World Health Organization (WHO) in 2017. From 2011 to 2015, 32 to 145 confirmed human cases of avian influenza A(H5N1) were reported to WHO annually (according to onset date). In 2016, there have been 10 cases in Egypt.*

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The statement from the summary, that ` Since November 2016 (as of February 6, 2017), 302 cases have been recorded in Mainland China' should be taken as a preliminary  accounting, since Hong Kong can only report those cases forwarded to them by Beijing or individual Provinces, and last Friday's release admittedly contained cases with onset dates as far back as January 4th.

Still, when you consider that last year only 121 cases were reported, this year is poised to produce a record number of H7N9 cases.

The case listing in today's report has 64 mainland cases, not 63 as the summary indicates, and some of the (already limited) data is missing from 23 of them, which are categorized as still `Under Investigation'. 

Nevertheless, we find that:

• 9 are listed as a fatal outcome
• 20 are listed as either in critical condition of suffering from `Severe Pneumonia'
• 8 are listed as having `Pnuemonia'
• 2 are listed in `Serious' Condition
• and the remainder are listed as `Under Investigation'

None of these cases are listed in either `good' or `stable' condition, something which we've only rarely seen mentioned this year. 

• The age skew to predominantly older adults continues, with only 4 of 64 cases (6%) aged 30 or younger (youngest age 26). 
•  And the gender skew towards males is even greater in this week's report, with 51 of 64 cases listed as male (79.6%) - an almost 4 to 1 ratio of male to female.  

While the causes of these demographic patterns are uncertain, it has been theorized that H7 viruses tend to infect, and cause more severe illness, in those born before 1968 due to childhood HA imprinting (see Science: Protection Against Novel Flu Subtypes Via Childhood HA Imprinting).

The gender skew heavily towards males might be accounted for by differences in occupational exposures to live poultry,  although once again, we lack sufficient data to make that assumption.

Since we know that H7N9 - like nearly all viral infections - can cause a wide range of illness, ranging from mild or asymptomatic to severe or even fatal, the assumption is that surveillance only picks up the `sickest of the sick'; those sick enough to be hospitalized and tested.

And this week's imported Taiwan patient - who went to the hospital for treatment three times - and was sent home (with at least one negative avian flu test), illustrates how difficult identifying H7N9 can be against a backdrop of seasonal influenza. 

We've seen estimates from researchers at the University of Hong Kong that the actual number of H7N9 cases may be anywhere from 10 to 200 times greater than are picked up and reported  by China's surveillance (see Beneath The H7N9 Pyramid).

Whatever the real number, so far we've seen no evidence (at least from the data we've been allowed to view) of sustained or efficient human-to-human transmission of the virus.   Close contacts of cases in Hong Kong and Macao - places where we tend to get much more detailed information - have remained healthy and uninfected.

All reassuring signs, despite what appears to be a record setting H7N9 epidemic in China.

But as last week's Updated CDC Assessment On Avian H7N9 reminds us, `of the influenza viruses rated by the Influenza Risk Assessment Tool (IRAT), H7N9 is ranked as having the greatest potential to cause a pandemic, as well as potentially posing the greatest risk to severely impact public health.'

So no one should be taking this year's outbreak for granted.