Saturday, January 21, 2017

Tracking H7N9: A Game Of Very Incomplete Information

Credit HK CHP


We are just 7 days from the height of the Chinese New Year's celebration, and already across much of China (in particular) and Asia (in general) many businesses and factories have shut down - sometimes for weeks - to enable hundreds of millions of people to travel home for this most revered holiday, where they will attend a reunion dinner with their families on the eve of the lunar New Year.

They stay a few days, then return to the cities from whence they came, travelling in crowded trains and buses - sometimes for several days.

All of this begins about 15 days before the Lunar New Year and runs for about 40 days total, during which time more than 2 billion passenger journeys will be made. Duck and chicken are, as you might imagine, popular dishes during these gatherings. And the live markets do tremendous business this time of year.

This happens during the regular flu season, as well as during Asia's yearly peak of avian flu. All of which provides numerous opportunities for flu viruses to hitch rides to or from different regions of Asia, and that in turn could potentially result in the creation of new reassortant viruses.

While this has been a perennial concern for more than a decade, this year we find ourselves in the midst of a unusually robust, yet poorly defined, H7N9 avian flu epidemic across much of Eastern China. 

Whereas during their 4th epidemic wave, China only reported 121 cases, over the past two weeks we've learned of nearly 200 recent infections (see HK CHP: Another 84 H7N9 Cases Reported By Mainland China). Details on most of these cases have not been released, making it nearly imposible  to keep track of, or compare to other reports we're seeing.

FluTrackers, which has maintained a terrific, fully linked, H7N9 case list since April of 2013 has been forced to temporarily halt tracking, simply because we don't have enough data to reliably keep track. 

Sharon Sanders, who spends hours each day keeping this (plus H5N1, MERS, H5N6, H9N2, etc) line listings as current and as accurate as possible, posted the following notice yesterday.
a. This line temporarily suspends the case count. The Hong Kong CHP announced receipt from China NHFPC a list of what they call "new" cases in the amount of 84, including 7 deaths. The onset dates range from December 15, 2016 to January 13, 2017. Hopefully the Hong Kong CHP will provide a detailed list of these "new" cases so that an analysis can be performed and an accurate count can be re-established. It is suspected that some of the "new" cases are previously known. Macao issued a press release saying the China NHFPC announced 95 new cases with the same onset dates as the Hong CHP report. More reason to suspend counting until we can get some clarity. link 

Hopefully, we'll get additional information next week that will allow Sharon and the newshounds at FT to continue to track cases, but the trend over the past two years from China has been to provide increasingly less information, and often only weeks after the fact.

A few provinces continue to post updates on their Health websites, while others are apparently only talking to Beijing.    

Which means that, over the next few weeks, we are likely to be dealing with inconsistent, fragmented, and confusing reports case counts coming from a number of different sources. 

It is also worth noting that we are likely only hearing about the `sickest of the sick', those who ended up in hospitals and were eventually tested for the virus.  No one knows how many mild, moderate, or asymptomatic infections go uncounted, although some estimates suggest we should be adding either one or two zeros to the totals (see Lancet: Clinical Severity Of Human H7N9 Infection).

Today, our best guesstimate is that there are something in excess of 227 new cases (HK CHP's tally) reported since November.  That number only goes through January 15th, and may not include all provinces. 

To put that in perspective, the 2nd epidemic wave (winter 2013-spring 2014) - racked up the highest number of cases (n=306) to date - with the bulk of those reported in January and February.   Given the lag in reporting, and the volume we've already seen, it seems likely that number will be breached in the next two weeks.

So far, from the limited information we have, we've seen no evidence to suggest the H7N9 virus is transmitting in a sustained or efficient manner from human to human.

While Beijing might not be quick to admit it if it had, I'm pretty confident Hong Kong's alert level would shoot up immediately were that the case, and we'd know something was afoot. 

Of course there's no guarantee that H7N9 will ever become a pandemic threat, but in last month's MMWR: Assessing The 4th Epidemic Wave Of H7N9 In China, researchers warned of `the continued geographic spread, identification of novel reassortant viruses, and pandemic potential of the virus' - stating that `using the Influenza Risk Assessment Tool (10), CDC found that A(H7N9) virus has the highest potential pandemic risk of any novel influenza A viruses that have been assessed.'

Granted, we could get blindsided by another swine flu virus - like we did 8 years ago - or by something completely from out of left field, but for the next few weeks at least, H7N9 and the impact of this year's Lunar New Year's travel season will be high on our watch list.  
Even accepting that the accuracy and completeness of the data we have are substantially less than we might  hope for.

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