Wednesday 14 May 2014

Keep calm and call the lab...without it, you know less than you think you do [UPDATED x2]

This morning there are 2 symptomatic healthcare workers (HCWs) in the United States (of America; I'm just going to use the "US" from from here on) who came into contact with the recently diagnosed MERS-CoV positive 44M (age and sex confirmed yet?) imported case.

The news has driven something of a twitter storm in the #MERS channel. Not unexpected I guess. The implication is that these 2 have acquired MERS-CoV from contact with the imported MERS-CoV-positive person. 

But that link is still far from proven yet. [UPDATE: both HCWs tested negative for MERS-CoV [1]]

This is a slightly revised version of that which I posted 18-March.
Thanks to Dr K Arden for helpful advice.
Click on image to enlarge.
VDU images are free to re-use. I can provide a better quality if needed.
Please just cite Dr Ian M Mackay, and this blog,,

if used elsewhere.
...Something to remember, or become aware of...

There are >200 known human viruses that have at one time or another been linked to patients with signs and symptoms that defined an 'influenza-like illness" (ILI). No-one can predict what these HCWs are infected with, but they have been or currently are infected by something. Lab tests are essential to know this.

I've asked Orlando Health's social media team (@orlandohealth) if these 2 HCWs are also being tested for the more "standard" 8 or 9 endemic human respiratory viruses/virus groups in parallel with MERS-CoV testing. I'll update this post with what I learn.

These standard viruses include influenzaviruses (A and B; red above), respiratory syncytial virus (dark pink), adenoviruses (orange), human metapneumovirus (pale pink) and parainfluenzaviruses 1, 2, 3 (purple). I'd also hope the rhinoviruses (in green above) since they are numerous and a frequent cause of ILI that can confound the very broad ILI tag. This panel of viruses comprise a standard testing menu which may be further extended, or shrunk, depending on the lab and they are included in commercial PCR-based kits. 

Keep in mind too that a positive PCR (if that's what is used) result does not mean the virus found is the cause of the illness. It may be that another virus, that has since dropped below the limit of assay detection was the cause, or a couple of viruses working in series or parallel, or a virus & bacterium working in synergy or a virus that wasn't tested for, or a virus that is not even known yet...pant.

But if these 2 HCWs do test positive for the MERS-CoV, it's not all that unexpected. Respiratory viruses on the scale you see above have not co-evolved with us/been introduced to us recently because they are easy to get rid of or stop from spreading between/to us.

MERS-CoV is just one of a long line of (probable) respiratory viruses that keep taking us to school to teach us just how sneaky and effective they can be at spreading and just how much our preconceptions trip us up, letting them finish with the best grade.

To stop the spread of them in an environment full of sick people, like a hospital, or even a school, a daycare centre, a long term care facility, a cruise ship, a plane, bus, or even a living room, is no mean feat. It's worth remembering that no single virus does only one thing. There is no "pneumonia virus", no "bronchitis virus", there's not a "common cold virus", there's no "droplet-only" spread, there's not "only replicates in nasal cells", there are just respiratory viruses and their very complex multicellular hosts. I'm happy to argue any of these points, but come prepared to show me that every avenue has been exhausted to support your argument beforehand. I'll give you the drum right now, they really haven't.

Respiratory viruses can each do lots of things and the outcome on our health is heavily determined by usour previous exposures, our age, our general health, our maternal antibody levels, our underlying diseases, our genetic makeup, our environment, our climate, our animal and human contacts, our personal hygiene and our habits.

End of monologue.



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