Wednesday, 11 September 2013

Can MERS-CoV seasonality tell us anything about acquisition of MERS?

Click to enlarge. Combined MERS-CoV cases for 2012 & 2013.
I'm the first one to say its way to early to be talking about the seasonal distribution of a new or emerging virus when there are only 124 cases worldwide. 

Right. 

Having said that, I thought I'd plot the cases by date of illness onset or (less satisfactorily) date they were first reported (even if that first was the report of a death). 

When combining the 15-months worth of case data for 2012 and 2013, the graph revealed a single "season" or at least larger numbers around summer in the Kingdom of Saudi Arabia (KSA). Because >80% of cases have occurred in the KSA, I have also listed a few festivals (some of which are frequented by camels) as well as the peak temperature variations and dust storm activity.1 

While I have no idea whether weather could be kicking up clouds of infectious CoV, it is an interesting co-occurrence, as are the presence of a number of festivals before case numbers spike. The Saudi Gazette commented that the risk of [acquiring?] bacterial and viral infections increases during dust storm season as do complication due to allergen exposure.

Of course we also know that some large clusters of cases have originated form hospital outbreaks and so environmental factors may play very little role at all. Or they might. Its impossible to say. But it is worth considering what could be happening up 2-weeks prior to a sharp rise in cases - if only to identify 1 index case that then ended up triggering a hospital outbreak.
  1. Dust Storms in the Middle East: Sources of Origin and Their Temporal Characteristics. http://ibe.sagepub.com/content/12/6/419.short
  2. http://www.magazine.noaa.gov/stories/mag86.htm
  3. http://www.saudiaramcoworld.com/issue/200803/heads.high.htm