Monday, 14 April 2014

MERS-CoV case age over time...[UPDATED]

The top chart uses a 10-day moving 
average (Excel)  shown as a dashed orange 
line. Sub-charts A, B and C are data taken from 
the identically boxed sections in the top 
chart with a simple linear trendline added 
in (dashed orange line).
Click on image to enlarge.
The next in my quest to answer myself is a look at the average age of Middle East respiratory syndrome coronavirus (MERS-CoV) cases over time.

I've made a new chart (top) showing the average age (orange dots) of MERS-CoV cases for each week (Week 1 being that which begins 19-Mar-2012) from 2012 until now. 

A couple of things strike me about the top graph.

  • There is a very small downward trend in the average age of MERS cases in 2014 (not shown but much more subtle slope than seen in the sub- charts, A, B and C) but nothing that screams "change in age of cases"! 
  • There does, at least by eyeballing the chart, seem to be an occasional cyclical nature to the ages of MERS-CoV cases. There are at least a couple of these apparent cycles (boxed as B and C) in which there seems to be a high'ish average age in a particular week, followed by weeks of mostly declining age. What could be causing this - if it's not just an observational bias [or influence from the cases lacking age data; thx @dspalten]? My hypothesis for this pattern is that index cases in clusters are older (comorbidities and older males have been a hallmark of severe MERS cases) and that the people they infect, or that form part of any human-to-human transmission chain in some way, are younger (healthcare workers and family) so the average age drops as infection spreads. To look at this in more detail I selected 3 sub-groups of the data and re-charted them in separate graphs (A, B and C). A was chosen because it did not obviously look the same as B & C to me, but I wanted to check. The linear trend lines for B & C support an overall decline in age in these 2 "cycles", but not for A.
  • In 2014 the pattern seems to have changed from one of cycles to what looks like a more consistent spread about an average age.
  • The average age for MERS-CoV cases from 2012-today is 52-years
    • It was 50-years, 12-Sept-2013 and 53-years, 26-July-2013.
    • In 2013 the average of all cases was 51.9-years; in 2014 so far its 52.2-years.
Age pyramid of all confirmed MERS-CoV cases.
Click on image to enlarge.
There are a few ages missing for some of the recently announced batches of cases, so it will be interesting to see how they impact on 2014, if we see those details come out. 

Someone with much better statistical skills than mine should possibly test these data and see if there is anything to this. From a pattern like this we just may learn what to look for to uncover the source, the mode of acquisition or routes of MERS-CoV transmission among clusters.

Or not.