After posting my recently updated charts on mortality and comorbidity rates among MERS cases, I received several questions regarding why there’s been such a sudden drop-off in both since the onset of the current outbreak. Here they are for quick reference:
Some have been suggesting that this might be the case because of the large number of asymptomatic cases that have been diagnosed since March 20th. As of today, exactly 2/3 of all asymptomatic MERS cases have been reported during the current outbreak – 52 of 78 total. This is a sensible hypothesis, given that 97% of asymptomatic cases thus far have occurred in individuals without pre-existing conditions and none of them have ended in death.
To test it out, I looked at mortality and comorbidity rates only among symptomatic MERS cases over the same three time frames as aforementioned: all-time (March 2012 to present); pre-outbreak (March 2012 to March 2014); and post-outbreak (March 20th to present). This is what I found:
Ok. It’s pretty apparent that even among symptomatic cases, mortality and comorbidity are much lower now than they used to be before the current outbreak began. Now, let’s quickly compare the numbers – all cases vs. symptomatic cases:
Hm. They’re a little different… But not by too much. As it stands, this means that the large number of asymptomatic cases that have been diagnosed since March 20th are probably not the main reason that rates of mortality and comorbidity have dropped off since the onset of the outbreak. [Of course, this might change as we learn more about the cases that are currently hospitalized.]
What we know is this: we’re seeing more cases without comorbidities now than we did before March 20th. Given that cases with comorbidities are 80% more likely to die from MERS than those without, this helps explain why mortality has been comparatively low since the onset of the current outbreak. However, we don’t yet know why otherwise healthy people are contracting MERS-CoV more frequently today than they were two years ago.
[…I guess we need another hypothesis!]
Note: Temporal data indicates date of onset, hospitalization, diagnosis, or public reporting.
Data Sources: KSA MoH & WHO