Kingdom of Saudi Arabia is MERS-free...is it MERS-CoV free though?

An article on news site France24 notes that no MERS cases are to be found in the KSA ahead of the imminent commencement date of the hajj; a gathering of pilgrims that is already well under way.

Great. And may that remain the case for the next few weeks.

And I tend to agree that there will not be any "mass spread" of a virus that still does not show that potential.

But the story avoids an important fact - while inadvertently spelling it out. 

There have been no severe cases of MERS - the disease - in the KSA in the lead up to the hajj. Severe enough to warrant triggering the strict measures...

"Employees have been given strict orders to isolate any suspected case and carry out the necessary laboratory tests" to ensure the safety of pilgrims on the hajj. 

To suspect, the Ministry of Health employees will first have to eyeball a fairly sick individual.

What about mild and asymptomatic cases of MERS-CoV infection? We know that they happen. We know that means at some point the person is likely to be shedding virus (at some level for some time period). We know transmission between humans is possible, albeit limited. We know of millions of pilgrims visiting the KSA so while the chance of a limited transmission event happening may remain the same, the total number of such events could rise. We know that we don't know where MERS-CoV is coming from. We know we have no idea how much, or little, MERS-CoV infection is in the "normal healthy" population in the KSA because that testing has not been done. We don't know much about the circulation or proportion of cases due to the other endemic CoVs in the KSA because epidemiology publications about general respiratory virus testing is limited.

So why is testing and isolation of patients still limited to severe cases? We don't yet know that mild/asymptomatic cases don't shed virus. So what we may potentially see in the coming weeks is many ambulatory new cases walking around shedding virus until they transmit to one of those older males who have 1 or more comorbidities. Then we see a 2:5 chances of that person dying from an infection they cannot explain getting because they were not in contact with a severe case or a likely animal.

While we do not know the primary source of the MERS-CoV - we do know that testing less ill people would let us answer an important secondary question; are the sporadic infections actually due to human-to-human transmission events that are simply not being identified or sought? This method of spread doesn't discount the viral genetic diversity we've recently learned of either. There could still have been multiple spillover events from animals - each may simply have spread more widely throughout the community than we know.

Please, please do some prospective testing. It would be an answer - and we have too few of those for MERS.

Thanks to @makoto_au_japon fr posting the link to the France24 article.