Credit CDC
# 8633
While a substantial portion of the MERS cases we’ve seen reported during the past few weeks appear to be related to hospital or healthcare exposures, we continue to see symptomatic cases admitted to the hospital with no mention of known contact with infected cases, medical facilities, or farm animals.
Admittedly, the information we get – particularly out of the Saudi MOH – is less than fully illuminating on these cases.
While better epidemiological investigations might yield other explanations, right now there would seem to be two likely sources of continued community infection.
The first being zoonotic; likely through direct contact with infected camels, or indirectly through contact with camel products (milk, meat, animal waste, etc.).
Previously we’ve seen genetic evidence presented suggesting multiple zoonotic introductions of the virus into the human population (see The Lancet: Transmission And Evolution Of MERS-CoV In Saudi Arabia) that – while warning that `human-to-human transmission is more complicated than expected’ – also quoted senior author Professor Paul Kellam:
“ . . . our findings suggest that different lineages of the virus have originated from the virus jumping across to humans from an animal source a number of times."
Making the idea of a `slow rolling spillover event’ at least plausible. But the author’s of this study also granted another possibility, `. . . there may be undetected (and possibly asymptomatic) people who could be carrying and spreading the virus.’
At the time that study was released (September 2013), there were just over 100 known cases of MERS, and nearly all were described as seriously ill or fatal. Mild or asymptomatic cases were beginning to be detected, but were still relatively rare.
Since then, more diligent testing and contact tracing has shown a much larger percentage of mild and/or asymptomatic infections. The chart below by Dr. Ian Mackay shows that among recent cases, about 20% are described as being `asymptomatic’ (see VDU blog Snapdate: MERS-CoV detected among asymptomatic people).
Since `asymptomatic’ is a subjective call, it is possible that some of these cases may have had some mild symptoms. And since KSA only seems to describe cases as being `asymptomatic’, `stable’, or `in intensive care’, we really don’t know how many `stable’ cases are symptomatic, but only mildly ill.
The difference between completely asymptomatic and `mildly ill’ could be significant when it comes to spreading the virus. While we know that influenza cases can be infectious 24 hours before becoming symptomatic, the jury is still out on whether asymptomatic (or pre-symptomatic) MERS cases can transmit the illness.
While I’m not aware of any studies that have been done to gauge the relative infectiousness of `mildly ill’ vs. `asymptomatic’ cases, it seems likely that those showing some symptoms would be more capable of spreading the disease than those displaying no symptoms at all.
And recent imported cases to the United States and the Netherlands confirm that `mildly ill’ cases can, and do, travel and mingle with people – often for days or longer. The latest MERS DON from the World Health Organization showed that the second Dutch case might never have been detected were she not part of the contact list of the first case.
This second patient has co-morbidities and developed first symptoms, including some breathing difficulties, on 5 May 2014 in Mecca, Saudi Arabia. Upon return to the Netherlands on 10 May, the patient presented with mild respiratory symptoms and fever, but these were not severe enough for her to seek medical help.
Presumably, there are some number of `mildly ill’ MERS cases going undetected in the Middle East, and while many may never pass on the virus to someone else, some probably do. Depending on such variables as viral load, the recipient’s genetic susceptibility to infection, co-morbidities, and other factors – the chain of infection may end there or continue on.
We’ve not seen the kind of exponential growth in MERS cases that would suggest highly efficient community transmission, but we are certainly seeing enough cases to conclude that some community human-to-human transmission is occurring.
And mildly ill (or possibly asymptomatic) cases may very well be behind this spread.
While obviously a concern for the community, these mildly ill cases are a greater threat to healthcare facilities, because when they do show up at a health clinic or doctor’s office, their symptoms are often not severe enough to set off alarm bells. They are viewed initially as having a common URI, or other viral infection, and can end up infecting healthcare workers, or other patients.
Hence the now standard warning to Healthcare providers from the WHO:
Infection prevention and control measures are critical to prevent the possible spread of MERS-CoV in health care facilities. Health-care facilities that provide for patients suspected or confirmed to be infected with MERS-CoV infection should take appropriate measures to decrease the risk of transmission of the virus from an infected patient to other patients, health-care workers and visitors. Health care workers should be educated, trained and refreshed with skills on infection prevention and control.
It is not always possible to identify patients with MERS-CoV early because some have mild or unusual symptoms. For this reason, it is important that health-care workers apply standard precautions consistently with all patients – regardless of their diagnosis – in all work practices all the time.
Droplet precautions should be added to the standard precautions when providing care to all patients with symptoms of acute respiratory infection. Contact precautions and eye protection should be added when caring for probable or confirmed cases of MERS-CoV infection. Airborne precautions should be applied when performing aerosol generating procedures.
Patients should be managed as potentially infected when the clinical and epidemiological clues strongly suggest MERS-CoV, even if an initial test on a nasopharyngeal swab is negative. Repeat testing should be done when the initial testing is negative, preferably on specimens from the lower respiratory tract.
While still a relatively minor threat outside of the Middle East, today HCWs are facing a new infection control challenge. One that may very well expand over the coming months and years, even if the MERS virus never gains greater transmissibility.
Over the past week we’ve learned more about the two imported US cases, and in both instances, they ended up waiting for hours in a hospital ER before being identified as potential MERS cases, and isolated. Apparently neither called ahead, or donned a surgical mask before entering the hospital.
Hospital workers, and other patients, were potentially exposed.
While none appear to have caught the virus, many HCWs were furloughed into home quarantine for the duration of the incubation period, and contact tracing and surveillance was instituted for other potential contacts. An expensive, but necessary, precaution.
Should MERS cases begin to turn up more frequently outside of the Middle East, we may very well have to re-examine our blasé attitudes regarding `mild’ respiratory viruses.
A good place to start would be posting notices on the door of every ER, doctor’s office, and clinic asking everyone who has any respiratory symptoms to don a surgical mask. Dispensers could be positioned at the entrance, along with the already ubiquitous alcohol hand sanitizer dispensers.
Frankly, why this isn’t standard operating procedure during every cold and flu season mystifies me. Seems like common decency to don a mask if there’s any chance you might be contagious to others . . .
Thirty years ago the sudden appearance of HIV and an increase in Hepatitis C ushered in new levels of infection control in hospitals and medical facilities. Exam gloves became de rigueur, and needle sticks became a constant fear. Gradually, HCWs became accustomed to these precautions, and they became the `new normal’.
The saving grace was neither of these viruses was airborne.
Today the emergence of MERS, and novel flu strains like H7N9 and H5N1, ups the ante. Which means that droplet and/or airborne precautions need to be added to standard precautions to prevent their transmission (see MERS, HCWs, And Infection Control). The trick is identifying which patients require these enhanced precautions.
Yes, we may get lucky, and MERS may eventually disappear.
But the reality is, eventually there will be viral threat to take its place; another pandemic influenza, a different coronavirus, or perhaps something completely out of left field. And in the meantime, common everyday respiratory viruses (Flu, RSV, adenoviruses, etc) already exact a heavy toll on the public’s health and the economy each year.
Which means that now is the right time to begin promoting better respiratory infection control and hygiene – both by the public - and by healthcare professionals.
It will pay big dividends both now, and in the future.
Besides, It really shouldn’t take a pandemic to get us to do the responsible thing.
