WHO team in Jeddah Investigation MERS - Credit @WHO
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This week a team from the World Health Organization is on the ground in Jeddah, where the largest concentration of MERS coronavirus cases has been reported to date.
Although their investigation is on-going and it is too soon to reach any conclusions, this morning WHO spokesperson Gregory Hartl suggested that fomites – inanimate objects and environmental surfaces –might be a significant player in the transmission of the MERS coronavirus.
While the role of fomites in the transmission of the virus has yet to be established (and indeed, its relevance may vary by location and/or cluster), it is probably worth taking a closer look at the environmental stability of the MERS virus, and how well it might be transmitted by contaminated surfaces or other inanimate media.
We have a pair of studies that address the survivability of the MERS virus outside of an animal host, and both suggest that – under the right environmental conditions – the virus remains viable for extended periods of time.
Three weeks ago, in EID Journal: Stability Of MERS-CoV In Milk, we saw a study where researchers inoculated various types of milk products (camel, goat, cow, etc.) and DMEM (a cell culture media) with MERS-CoV strain Jordan-N3/2012, stored multiple samples at 4°C or 22°C, and then tested their infectious disease titers at 0, 8, 24, 48, 72 hours post dilution.
Their results?
At 0–72 hpd, virus titers decreased significantly only in goat milk (p = 0.0139, 1-tailed paired t test) and DMEM (p = 0.0311) but not in dromedary camel milk (p = 0.1414) or cow milk (p = 0.2895). Samples stored at 22°C showed a greater loss of infectivity than did samples stored at 4°C.
Making unpasteurized milk at least a plausible medium for carriage of the MERS virus or its transmission to humans. Unknown at this time is whether camels shed the virus in their milk, a project that Dr. Ian Lipkin’s group at Columbia University is reportedly going to tackle next.
Another study, going back to September of last year, appeared in the journal Eurosurveillance: Environmental Stability Of MERS-CoV. Here researchers looked at the environmental stability of the MERS coronavirus, both on surfaces (fomites), and as an aerosol.
The researchers describe their experiments below (slightly reformatted for readability).
In this study, the stability of MERS-CoV (isolate HCoV-EMC/2012) was evaluated under three different environmental conditions:
- high temperature and low humidity, 30°C – 30% relative humidity (RH);
- high temperature and high humidity, 30°C – 80% RH
- and low temperature and low humidity, 20°C – 40% RH
to reflect a wide range of environmental conditions including an indoor environment (20°C – 40% RH).
The stability of MERS-CoV under the three tested environmental conditions was respectively compared with that of influenza A virus A/Mexico/4108/2009 (H1N1) originating from a human isolate obtained during the influenza A(H1N1)pdm09 pandemic in 2009 [9]. The stability of the two viruses in aerosols at 20°C with 40% or 70% RH was also assessed and compared.
The results?
- While the Influenza A virus became non-viable on steel and plastic surfaces in less than 4 hours for all testing environments, the MERS virus survived 48 hours in the 20°C – 40% RH environment. Survival of the coronavirus at 30°C – 30% RH was 24 hours, and 8 hours at 30°C – 80% RH.
- As an aerosol, the MERS virus remained very stable at 20°C – 40% RH, while its viability decreased (89% – comparable to the Influenza A virus) at 20°C – 70% RH.
The full study can be found at: Stability of Middle East respiratory syndrome coronavirus (MERS-CoV) under different environmental conditions by N van Doremalen1, T Bushmaker1, V J Munster.
The bottom line, under favorable temperature and humidity conditions (such as you might find in an air conditioned hospital), the MERS virus survives quite well on surfaces, and in the air. This may help explain the high rate of nosocomial outbreaks we’ve seen in the Middle East.
While the route of infection with this virus has not been determined, this virus shows the kind of environmental hardiness that would be conducive for either fomite or droplet/aerosol (contact) transmission.
When the WHO’s mission in Saudi Arabia is completed, and they’ve had time to look at the data they’ve collected, we should have a better idea of what is going on with this virus.
Stay tuned.
