In some welcome news, for the first time in more than a month the Saudi capital of Riyadh is reporting no new MERS cases, but at the same time the cluster in Al-Madīnah (aka Medina) has grown by three, including two health care workers.
According to today’s report, 2 of the cases have been transferred to Riyadh hospitals.
The original source of the outbreak in Madīnah is a bit murky, as all of the cases announced to date have been listed as `contacts of a confirmed or suspected’ case. Of the 5 cases so far, 3 are listed as HCWs.
The pattern we’ve seen so often in Jeddah, Taif, Hofuf, Riyadh, Jordan and South Korea appears to be repeating in Madīnah, with hospitals serving to amplify MERS outbreaks.
While sporadic community acquired cases continue to crop up, it has been the large nosocomial outbreaks – often involving scores (even hundreds) of cases – that have been the primary driver of MERS over the past 16 months.
Although hospital clusters have figured prominently in the spread of MERS since it first emerged more than three years ago, the frequency and size of these clusters has increased markedly, starting noticably in the spring of 2014 (see chart below).
We are now roughly 40 months since the (retrospective) discovery of MERS in humans, and during the first 20 months, there were fewer than 200 confirmed MERS cases in the world. During the second 20 months, we’ve seen more than a 7-fold increase in cases, with now over 1,540 known infections.
During those first 20 months, a large nosocomial cluster might have involve a dozen cases. Since the spring of 2014 we’ve seen repeated hospital clusters with 80, 100, even as many as 180 cases (in places like Jeddah, Taif, Hofuf, Seoul, Riyadh, etc.).
Why hospital outbreaks should be substantially larger – and seemingly harder to stop - than they were 2 years ago begs a lot of questions, including:
- Have infection control procedures somehow become less effective, or their implementation less rigorous?
- Has the virus changed to become more transmissible? ( see mBio: Origin & Possible Genetic Recombination Of MERS-CoV – China)
- Are `missed’ asymptomatic cases driving these clusters?
Unfortunately, the answer to these and other pressing questions have been slow in coming out of Saudi Arabia, where the vast majority of cases have occurred (see WHO Statement On The 10th Meeting Of the IHR Emergency Committee On MERS).
While MERS currently falls short of being global public health crisis - looking at the numbers - it is also hard to come away with much reassurance that we making progress in its control.