Saturday, 9 November 2013

MERS-CoV by the numbers: recent weekly case activity...

Click to enlarge.
Confirmed MERS-CoV cases (green) and
deaths (red) each week. Case numbers
are listed on the y-axis (side), days of each
week along the x-axis (bottom). Case dates
are derived from announced date of onset
but if absent, on the date of reporting.
This follows on from my previous post (you can follow its links to earlier weekly charts) about lab-confirmed Middle East respiratory syndrome coronavirus (MERS-CoV) cases, plotted by week.

These charts are based on the reports that get into the public domain. Those of us trying to follow and deconvolute MERS-CoV case information pretty much all agree that the data are terrible, but they are what they are. For example, the data are currently absent details on 2 MERS-related deaths for which no links to our case lists can be found. There are 85 cases missing date of disease onset data (which makes these charts imperfect), 8 without an age, 10 without a sex and most have no date of hospitalisation or date of lab confirmation. As I've bemoaned before, a standardised numbering of cases would be helpful too. Among other things.

The charts suggest there is not a lot of activity in terms of new cases, and the number of deaths, thankfully, remain much lower than during the weeks preceding my post in early September.

You can see that during the Hajj (13th-18th of October), there were 3 cases and a death described but in the weeks immediately afterwards, there has been no spike in cases of MERS. What makes this a significant development is that, for the second time since we learned of MERS-CoV, countries outside the Kingdom of Saudi Arabia (KSA) have had a direct hand in the observation and testing of pilgrims. This adds some confidence that severe symptomatic MERS is a relatively rare disease and one that does not spread quickly and efficiently. We have no real data to say that virus doesn't spread quick, widely and efficiently however, just that the severe infection outcomes don't.

So, no sign of a major jump in new cases. In this 4-week period there have been 13 cases which is up 2 from the 4-weeks before that. There have been 3 deaths (PFC of 23.1%, well below the total average of 41.3%) in this period, down from 4 in the previous month.

These numbers still have to be considered with care. This week's Spanish case really shone a light on the issue of laboratory unconfirmed cases of clinically diagnosed pneumonia circulating in the KSA. And where there is one such case there are likely to be others. Many others? We don't know.

So with 155 cases and 64 deaths in 87-weeks, MERS seems to be ticking along, but it shows no signs of becoming a widespread health issue. While it has a PFC of 41%, that is a meaningless number until we start testing more widely than is being done now. There are still many questions to answer about its host, how humans acquire it, whether its widespread in the community - but on the topic of transmission, MERS does not look likely to become a pandemic any time soon.