Saturday, 26 April 2014

An update on the April outbreak of MERS-CoV...

We are in week 110 of the MERS-CoV outbreak event, that's 2.12 years and 386 cases including approximately 113 deaths (PFC of 29.3%, the lowest to date) since the first known cases became ill in Mar of 2012.

Just a few quick charts to keep track of things.

Virus detections continue to accrue at a double-digit rate, as has been the case each day except 2 (one of which was blip) between 18-Apr and 25-Apr this year. Thanks mainly to the Jeddah outbreak (no more calling it a "cluster")
Click on image to enlarge.

I've added the Mazayin Dhafra camel festival (United Arab Emirates; UAE) to the regional acquisition chart. It's a gathering that brings together ~17,000 camels. [1-6]
Thank you to @_abdullah88 and David Leith


Click on image to enlarge.
In the next 2 charts we can see the large and rapid rise in number of detections over the past 3 weeks, firstly by week. The cumulative average has also jumped (now at 2.88 cases per day across the entire period of MERS-CoV's emergence) as detections continue in higher numbers than ever before.
The underlined region (green) includes those detections which have
not yet passed through the World Health Organisation and
been "officially" announced to the world. His process usually,
and until late March, consistently, added valuable additional data.
Click on image to enlarge.


In the next chart we can see the zoomed in daily story for late March to April detections. That cumulative average (grey line) is steadily climbing but not at an exponential rate. We wait and see if human-to-human transmission increases as each of these cases makes contact with other people and the incubation period clock starts. If the virus is spreading even more efficiently than in 2013, that daily curve might start to look more like the weekly curves. Another few weeks should answer that for us.


Click on image to enlarge.
Healthcare worker (HCW) numbers have risen sharply (see below) during the April outbreak to a total of 84 detections, 7% of whom have died. 

Deaths (left) among HCWs now represent 1.6% of all MERS-CoV positive deaths. This jump in HCW detections has been fuelled by the Jeddah outbreak but also by the parallel HCW cluster among paramedics in the UAE; two as yet completely unexplained events.
Click on image to enlarge.

As ever I must note that the data are full of holes. 

In particular, the past 140 or so detections, despite being announced through a Ministry, lack sex, date of illness, date of hospitalisation or precise dates of detection if they were not ill (of which there have been a number of late).

This increasing number of detections may simply be due to increased testing of contacts, as we learned from comments by Dr Memish this past week.[7] Apparently until relatively recently, and despite comments that suggested more KSA laboratories were coming online made as far back as July/August 2013, contacts of confirmed cases have been mostly observed for signs of disease, and not sampled for laboratory testing. Testing has been limited to cases of pneumonia. This seems to conflict with recent accounts of larger sample numbers being tested (which I don;t have citation for right now), unless pneumonia is far more widespread in the Kingdom of Saudi Arabia (KSA) than we understand. 

Testing is key to understanding how widespread MERS-CoV is in the community and how well it actually transmits from human-to-human (-to-human-to-human- etc). 

It's not at all surprising that clusters spread and are not shut down quickly if no-one knows who has MERS-CoV and who has influenzavirus or rhinovirus or another coronavirus or even who has a MERS-CoV-positive mild yet perhaps still contagious infection that doesn't rate a second look. You can never understand an emerging virus when you miss out people that are infected-whatever their clicnial presentation. 

The previous level of limited and biased (toward only the most severe of disease) testing is reserved for say, annual influenza surveillance; a well known virus that circulates seasonally, as we fully expect it to, and for which we sample a sliver of the community pot. This are the cases that go to hospitals or just to family doctors, get tested, some viruses go on to get subtyped and we can use those proportions to extrapolate what's going on with that well-known human virus, to the rest of the community. We cannot do that with MERS-CoV yet because we don't know our enemy like we know influenzavirus.

Another point to make is that right now, the flurry of detections may be just a flurry of testing; better testing more accurately representing MERS-CoV circulation among humans in the KSA. A community-based study testing milder disease is essential to answer that. 

In the meantime we're left hanging between wondering whether changes to testing approaches is the reason for being about to reach the 4th 100 MERS-CoV detections in record speed, or whether it is a change in the virus that lets it spread better and further. Of course we don't know how many "rounds of infection" are going on with MERS-CoV just now because we are lacking information about how cases are linked together; who got infected from whom? Is it from a case to just a single close contact, or from a case-to-person-to-person-to-person....? 

Also, what is happening in camels during the first quarter of the year when MERS-CoV detection in humans seem to be at their lowest? It's now pretty clear that humans can acquire MERS-CoV from camels thanks to a recent article in Emerging Infectious Diseases by Dr Memish and colleagues that indicate a quite clear direction to acquisition.[8] But do camels undergo a seasonal outbreak of MERS-CoV and is that a regular and recurring thing? Is it related to camel festivals? Is it what has started the human infection waves in in April 2013 and 2014? We'd need widespread and ongoing camel (and human) testing to understand that. What about camel milk and urine; drunk regularly or used / collected / drunk for various reasons, respectively? Is it harbouring untold reserves of infectious MERS-CoV that gets ingested, then manifests in the vast majority of cases as a respiratory disease? We'll need some testing of those fluids to answer that, and perhaps a little common sense to interpret the results.

As usual, I present you the best of the data that I can lay my hands on yet find myself unable to give you many actual answers. At least I'm not alone in that so enjoy the hand-waving! 

One fact that I can share; the communication of events during what might be the most significant outbreak and cluster of cases of MERS-CoV to have happened in 2-years has been horrible, even by MERS epidemiology standards. 

Couldn't happen at a worse time really. Let's hope the new management at the KSA Ministry of Health have been awakened in time to avert an event on a much more global scale.

Sources...

  1. Avaxnews | Mazayin Dhafra Camel Festival | 21-Dec-2013
    http://avaxnews.net/touching/Mazayin_Dhafra_Camel_Festival.html
  2. Mazayin Dhafra Camel Festival | ABC Australia news | 21-Dec-2011
    http://www.abc.net.au/news/2011-12-21/emirati-men-look-through-a-fence-at-the-mazayin-dhafra-camel-fe/3741618
  3. Daly Mail UK | Even the winner of this competition will have the hump: Hundreds of camels snake their way through the desert for a beauty contest | 24-Dec-2013
    http://www.dailymail.co.uk/news/article-2528868/Theyve-got-humps-Hundreds-camels-snake-way-desert-theyre-driven-beauty-contest-Abu-Dhabi.html#ixzz2zxdhAqNb 
  4. DailyMail
  5. http://www.dailymail.co.uk/news/article-2528868/Theyve-got-humps-Hundreds-camels-snake-way-desert-theyre-driven-beauty-contest-Abu-Dhabi.html
  6. Newser.com | Dubai Sheik Pays $2.7M for Camel | April 2008
    http://www.newser.com/story/23945/dubai-sheik-pays-27m-for-camel.html
  7. Sydney Morning Herald photos of Mazayin Dhzfra festival| 23-Dec-2013
    http://www.smh.com.au/photogallery/travel/the-spectacular-mazayin-dhafra-camel-festival-20131223-2zu5b.html
  8. Soaring MERS Cases Cause Pandemic Jitters, but Causes Are Unclear
    http://news.sciencemag.org/health/2014/04/soaring-mers-cases-cause-pandemic-jitters-causes-are-unclear
  9. Human Infection with MERS Coronavirus after Exposure to Infected Camels, Saudi Arabia, 2013
    http://wwwnc.cdc.gov/eid/article/20/6/14-0402_article.htm