Saturday, April 20, 2013

H7N9: The Riddle Of The Ages



# 7169


Were it not killing people, and imbued with a worrisome (but as yet, undetermined) potential to spread further, I suspect that many flu researchers’ reaction would be to peer Spock-like at this emerging H7N9 avian flu virus, arch an eyebrow and mutter, `Fascinating’.


Like H5N1 before it – and to a lesser extent the H1N1 pandemic strain of 2009 - this new virus is challenging conventional wisdom on how novel flu viruses should behave.


Last night, Robert Roos – Editor of CIDRAP NEWS – wrote on an analysis performed by Nick Kelley, PhD on the unusual age and gender demographics of the 90+ patients identified to date.


Thus far, we’ve seen a skewing of age and gender in H7N9 patients towards elderly males, something which has been an ongoing topic of speculation both publicly and privately in the flu world for a couple of weeks.


It’s a good report, with extended remarks from Michael Osterholm, director of CIDRAP.  Follow the link, and I’ll have more when you return.


H7N9 mystery: Why does age profile tilt older?

Robert Roos * News Editor

Apr 19, 2013 (CIDRAP News) – One of the odd mysteries posed by the H7N9 influenza virus emerging in China is why most of the patients are on the older side—a fact that stands in sharp contrast to the pattern seen with that other deadly crossover avian virus, H5N1.


An analysis by Nicholas Kelley, PhD, at the University of Minnesota's Center for Infectious Disease Research and Policy (CIDRAP), publisher of CIDRAP News, shows that the median age of H7N9 case-patients thus far is 61.5 years, with a range of 2 to 89 years.


For comparison, Kelley examined the ages of the 45 H5N1 case-patients in China over the past 10 years and found a median age of only 27. And when he looked only at H5N1 cases in the same provinces where H7N9 cases have turned up, the median age was even younger: 24.


The European Centre for Disease Prevention and Control (ECDC), in an epidemiological update released today, but based on cases as of yesterday, put the median age of H7N9 patients even higher: 64, with a range of 4 to 89.

(Continue . . . )


The following chart shows the stark contrast between the age groups impacted by H5N1 and H7N9, both avian flu viruses.  


The predilection of the H5N1 virus for younger patients has evoked a number of theories, but has never been adequately explained.


Another chart, this time from Dr. Ian MacKay’s excellent Avian influenza A virus H7N9 webpage, illustrates the pronounced trend towards male patients as well.



This graph shows the proportion of males (blue bars) and females (violet bars) contributing to total cases (including deaths) and to fatal cases alone.


There are other mysteries with this virus as well, for which answers (thus far) have been few. Among them:


  • Why would a low pathogenic avian virus produce such severe symptoms in humans?
  • With so few birds testing positive, what are the primary (or hosts) for this virus?
  • How is this virus currently spilling over into humans?
  • Are there substantial numbers of mild, or asymptomatic infections going uncounted?
  • Geographically, how widespread is this virus?
  • Is human-to-human transmission taking place?
  • How rapidly is this virus mutating? How many clades exist?
  • What is this virus’ pandemic potential?



Over the past 24 hours Gregory Hartl, spokesperson for the World Health Organization, has been fielding a number of these questions on Twitter. While solid answers remain elusive, a few of his responses below.




Sometimes the hardest answer to give is, “We don’t know yet.”  It may disappoint, but it has the virtue of honesty.


Yet, when you consider that scientists have been studying the H5N1 avian flu virus for more than 15 years – with many questions still unanswered - the amount of information we’ve learned about H7N9 over the past 3 weeks is actually quite impressive.


With yesterday’s announcement that WHO: H7N9 Team Lands In China, hopefully we’ll be getting an even better idea of how this virus behaves – and how much of a threat it poses – over the next couple of weeks.

Stay tuned.