Friday, 10 January 2014

H7N9 cases by week...the other bird flu is done nesting [UPDATED]

Click on image to enlarge.
H7N9 cases by week, worldwide, from Week
beginning Monday 30.09.13 to 06.01.14.
Sources are publicly available data. 
A quick plot of case occurrence to the best of my ability given the variability in the data. Follow the left-hand column down then back up to the top of the right-hand column and down again to follow the 22 cases and 2 deaths through time.

I started with Week #33 (33rd week of H7N9; given that Week#1 starts from Feb-18; the week in which symptoms were reported for the 87-year old male index case on Feb-19 [updated]). Prior to Week #33, things were very quiet going back to April-2013. A couple of cases in July. 

These charts will change as we get more cases and more details and perhaps, more fatalities among these cases. There are between 152-158 H7N9 lab-confirmed cases, including fatalities.

The main message here is that H7N9 case numbers are on the rise again

It was in March and April 2013 when we saw the greatest number of H7N9 cases, but given that we now have specific PCR-tests and other assays available combined with a far greater number of "launch sites" this year, I expect we'll see increased numbers of human cases from here on in. That could change if drastic control measures are taken of course.

We have also learned from the recent case in Canada, that H5N1 is probably entrenched in areas that are not being tested/reported (see CIDRAP article). There is no doubt in my mind that H7N9 will be in the same nest, circulating in at least the 12 provinces or municipalities of mainland China from which we have seen human cases arise over the past 49-weeks. 

Speaking of which, there have been very few deaths in this approximately 15-week block. The overall proportion of fatal H7N9 cases was around 30% but among the subset of cases here, only 9.1% have died after H7N9 infection. 

Have things changed? 

I can't imagine the virus has changed since it seems most acquisitions are from poultry and there would not be evolutionary pressure in a bird to transmit more efficiently on the off-chance it was acquired by a human! So does this mean...

  • Case management has improved?
  • Are more cases recovering and being discharged?
  • Are we still in that horrible waiting period when cases are in intensive care awaiting their fate?
  • Are we simply not getting details about deaths and discharges from China any longer? 
We were certainly missing information about which cases died towards the end of the first wave of H7N9 - my database can only identify 37 of the predicted 48 deaths. These details have not yet appeared in the scientific literature so any averages (sex, or age for example) calculated from public sources are far from perfect. I presume Chinese researchers have those data.