While the MERS outbreak in Saudi Arabia has been winding down, I’ve been retroactively adding newly announced deaths to previously reported cases. (Given the ~15 day lag time between onset of symptoms and death, I expect that there’ll be more deaths to add to the tally in the days ahead.)
Recently, I was able to match the vast majority of deaths announced thus far to their respective database case entries, giving us a clearer picture of what case fatality rate has really looked like in recent weeks. As of today – May 27th – only 5 deaths remain unmatched, all from the KSA. It’s certainly possible that I’ve mismatched some of these retroactively-added deaths, despite stringent triangulation using age, gender, location, and (more recently) reporting date data. This said, I feel confident enough in the data as they stand today to share an up-to-date “redo” of the comorbidity/mortality relative risk analysis I first conducted about a month ago.
Note: In the original analysis, I used all (symptomatic + asymptomatic) cases; however, I’ve included only symptomatic cases in the following relative risk calculations. This choice reflects some of the important trends that have surfaced among MERS diagnoses recently – namely, that nearly a quarter of all cases reported since the Spring 2014 outbreak began have been asymptomatic. Because asymptomatic cases won’t be dying of MERS (as far as we can tell for now, that is), I thought it would be best to consider how comorbidity impacts mortality specifically in symptomatic cases this time around.
As before, I looked at three different time frames: from March 2012 (when MERS was first documented) to present; before 3/20/2014 (the onset of the current outbreak); and after 3/20/2014. This is what I found:
Overall, cases with comorbidities are +67% more likely to die than those who are otherwise healthy.
Prior to the current outbreak, cases with comorbidities were +53% more likely to die than otherwise healthy cases – a bit less than what we saw above…
…Which makes sense when we take a look at the current outbreak, during which cases with comorbidities have been +74% more likely to die than those without them.
Note: With regards to this last statistic in particular – if you ventured to take a look at the original analysis, you’d discover that this result is contrary to what I found a month ago. The reason for this is pretty straightforward. Remember that lag time I mentioned between onset of symptoms and death? Well, when I first posted this analysis (4/27/14), it was just a week after the outbreak peaked (4/21/14); since then, many cases reported on and around that date have retroactively been demarcated as deaths. (Moreover, this new analysis considers only symptomatic cases AND includes previously unmatched deaths.)
So, what does this all mean? In my opinion, there are three important takeaways:
1. Individuals with pre-existing conditions (such as diabetes & heart disease) are more likely to die from MERS than cases who are otherwise healthy.
2. Despite estimates from late April that suggested otherwise, this relationship appears to have been especially pronounced since 3/20/2014 (though still within reason when taking confidence intervals of both the pre- and post-outbreak analyses into consideration).
3. Mortality data (inevitably) becomes more complete with time; it’s possible that this relationship will become even stronger as we learn the fate of cases that are currently hospitalized.
…But wait! It’s important to note that the impact of comorbidity on mortality may very well be confounded by factors such as age and sex. With this in mind, I’ll be taking a closer look at these two variables in the coming days. Stay tuned!
Note: Temporal data indicates date of onset, hospitalization, diagnosis, or public reporting.
Data Sources: KSA MoH & WHO