Monday, 8 June 2015

MERS-CoV and opportunity to spread...

1,500 people were exposed via direct or indirect contact, to one Doctor who was already ill and later tested positive for the Middle East respiratory syndrome coronavirus (MERS-CoV).[1]

So what?

If this were measles virus - that sort of exposure could spell disaster for infection control and measles containment. In measles, every infected person can infect about 18 other people...but that's an average of course and on an individual basis, the number of new cases can move around that value depending on the number of contacts each person has...and the type of contact...and how much virus the index case sheds... and everyone's their immune function...etc, etc, etc.

But MERS-CoV ain't no measles virus. 

Time and again we've seen that MERS-CoV does not pass easily to new people. Around 4% of household contacts were deemed infected, across 26 households,  in a study from 2014.[2] About 2-3% in some other analyses.[3] And by 'easily' I mean lots and lots of contact becoming ill from each case they are exposed too. If 4% of those 1,500 hundred contacts of the South Koran Doctor had been exposed to an infectious dose of MERS-CoV from this Doctor - who really does get around - and the incubation period is as short as the 3 or 4 days it has been in some cases in South Korea...then any minute now, we'll expect to see 60 more cases in the community and in hospitals, all with links to this health professional. 

I'm not holding my breath (pardon the pun) for this though, because I doubt the contact was often very close. I also won't go into the fact that there maybe no actual testing of contacts happening - we have no idea of that aspect of the South Korean incident. I really hope the South Koreans are testing. It would be a great study producing some valuable transmission data outside of Saudi Arabia. And not just PCR testing but collecting blood for serology (antibody studies) testing later too.

Google tells me that South Korea has a population of 50,220,000 in 2013. So there have been 87 cases of MERS since May...about 0.0002% of the population are infected. At this point, perhaps we should start assembling a list of how many people went through the hospitals with the most cases, that did not acquire MERS-CoV...just to provide some added context to the cluster. In other words - the past few days have seen case numbers growing day on day - but infections are still contained within the hospital setting. Close contact. No community spread. No camels infected in zoos.

Tomorrow is another day and we'll see what is added to the tally resulting from the arrival of a single infected traveller.

References..

  1. http://www.koreaherald.com/view.php?ud=20150604001315 
  2. MERS-CoV around the house-yes, it does transmit at home
    http://virologydownunder.blogspot.com.au/2014/08/mers-cov-around-house-yes-it-doers.html
  3. If this is what MERS-CoV detections look like with more testing...what is the "normal" community level of virus?? [UPDATED]
    http://virologydownunder.blogspot.com.au/2014/04/if-this-is-what-mers-cov-detections.html