After sharing my last post on MERS mortality, I received several questions about whether the rate of comorbidity among cases has changed since the onset of the current outbreak in the Middle East. To address this, I reformulated all three graphs by adding a third layer called “Cases with Comorbidities”. From March 2012 – when MERS was first documented – to present day, here’s what’s been going on:
A third of MERS cases in this time frame have had other pre-existing conditions (such as diabetes, heart disease, etc.) before contracting MERS-CoV. It really does seem to manifest in otherwise healthy individuals less frequently. After taking a look at this, I removed this past month (April 2014) from the analysis to see what the rate of comorbidity among MERS cases was prior to outbreak we’re seeing right now in Saudi Arabia and the UAE:
40% of MERS cases between March 2012 and March 2014 have had comorbidities. It’s important to note here that not all deaths due to MERS were in cases with pre-existing conditions, though I do suspect that the rate of mortality is higher in such individuals when compared to those who are otherwise healthy. (I’ll run the numbers on that matter sometime tomorrow.) Nevertheless, 40% is quite high. Next, I looked at the same rate among the cases we’ve seen since the outbreak began around March 20, 2014:
We find that this past month or so, only about a quarter of MERS cases have had comorbidities – significantly less than before the outbreak began. This may – at least in part – explain why the mortality rate has also been so much lower since March 20th. That said, I’m beginning to wonder whether this piece of the puzzle may be related to the larger number of asymptomatic cases that have been diagnosed since the start of the outbreak; 62% (43 of 69 total) of all asymptomatic MERS cases have been reported this past month alone. One thing’s for sure: increased screening of vulnerable groups – such as healthcare workers and direct contacts of diagnosed MERS cases – is most certainly contributing to the shifts we’re seeing in rates of mortality and comorbidity. Whether these shifts are reality – or simply an artifact of heightened surveillance – remains uncertain for the time being.
Note: Temporal data indicates date of onset, hospitalization, diagnosis, or public reporting.
Data Sources: KSA MoH & WHO