Most virologists would probably tell you that enveloped viruses are generally pretty fragile outside of their host and so wouldn’t survive for long on dry surfaces. They may well say “If you were talking about a non-enveloped virus (like norovirus) then, yes, it would probably survive on surfaces for quite a while. But enveloped viruses, no – you’d be lucky if it survived for more than a few hours.” But when I looked at the literature to investigate the potential for dry surface-mediated transmission of respiratory viruses with pandemic potential (SARS, MERS and influenza), the picture that emerged was quite different. These respiratory viruses can survive on dry surfaces for ages, and the contaminated environment may well be an underestimated reservoir for their transmission. This is summarised in a review published recently in the Journal of Hospital Infection.
Laboratory studies show that SARS-CoV, MERS-CoV and influenza virus can survive on surfaces for extended periods, sometimes up to months. Environmental sampling in field settings has identified contamination with SARS-CoV and influenza virus (no studies yet for MERS-CoV), but important to note that many of these studies used PCR to detect the virus, so there is often no way to tell whether the virus is alive or not. At the very least, detection of nucleic acid is a marker of shedding.
The figure above summarises the complex transmission routes of respiratory viruses. They are emitted as a ‘cloud’ containing a whole spectrum of particle sizes, from tiny droplet nuclei, which aerosolise, through to large, wet droplets. It is likely that both play a role in transmission. And they also come out of the other end (in faeces) is startlingly high numbers (e.g. 109 virus particles per gram of stool for SARS-CoV), raising the potential of faecal-oral transmission. Given the various potential routes of transmission, it is very difficult to disentangle which is most important. There is some compelling data from mathematical and animal models, and from intervention studies that contact transmission can be the most important route. But this is virus – and context – dependent. If you have 20 people in a lift, then the air is likely to be the most important vector. But if you have two people whose only epidemiological connection is shared contact with the lift call button, then surfaces are the only potential transmission vector.
Having now reviewed this extensive and wide-ranging and interesting literature, I have settled on the view that surface contamination is an important potential reservoir for transmission of these respiratory viruses, so should not be underestimated from an infection prevention and control viewpoint.