While winter is on the wane, our viruses of winter are still not finished with us yet. With a few more months of the cold and flu season left, SARS (Severe Acute Respiratory Syndrome) is trying to rear its all too ugly head. As the CDC pointed out in the video attached to the blog of a few weeks ago, besides norovirus, wintertime brings a host of respiratory infections including Influenza, respiratory syncytial virus (RSV), rhinovirus, and viruses responsible for viral pneumonia.
Coronaviruses in Viral Pneumonia and SARS
Of winter visitors (all of which spill into spring) respiratory viruses are responsible for approximately a third of all adult cases of pneumonia and 15% of childhood infections reported. These are classed as viral pneumonias with the most commonly implicated viruses being: rhinovirus, coronaviruses, influenza virus, RSV, adenovirus, human parainfluenza virus (hPIV) and the recently identified human metapneumovirus (hMPV).
Besides the coronavirus types causing common colds, we are seeing headlines from the UK for the 12th case of SARS caused by another virus in the group. Six of the 12 cases seen globally (8 in the Middle East & 4 in the UK) have been fatal (50% mortality) and is all too reminiscent of the 2002 SARS outbreak, that infected some 8000 and claimed around 800 lives. The WHO is referring to this as a novel coronavirus or NCoV and while concerned, public health authorities are not seeing sustained transmissions but recommend testing and investigation for the virus if any unexplained pneumonia cases or clusters of severe acute respiratory infections are experienced regardless of where they occur. Britain's Health Protection Agency has said while it appears the virus can spread from person to person, "the risk of infection in contacts in most circumstances is still considered to be low."
Understanding Winter Viral Infections
Why winter? Well first off, viruses like our DNA and protein containing foods such as fruit, vegetables, meat, fish and eggs survive better refrigerated. Indeed these cold dry conditions increase survival times for all viruses across the board but there are also other factors favoring transmission.
In addition, cold dry conditions pull moisture out of aerosolized droplets released by coughs and sneezes, resulting in respiratory viruses (and norovirus) able to float in the air for longer periods during the winter.
These same conditions also tend to dry out the nasal passages with negative consequences making virus transmission more successful. It seems the mucous membrane in our noses serve as a primary defense with mucous being a rich source of antibodies and natural antimicrobial molecules. In addition damaged mucosal cells, permit easier entry of upper respiratory viruses such as those causing the common cold and flu, into the body.
Cold winter climates cause large numbers of people to stay indoors in more habitable temperature controlled environments. This means people are crowded into highly populated places where opportunities for transmission of infectious pathogens is increased via sneezing and coughing and contaminated surfaces.
And finally, if all of the above were not enough, all of our respiratory viruses of winter are easily inactivated by sunlight, in short supply in winter months.
What Makes these Respiratory Viruses Tick
There is a great deal of commonality with all of these viral infections of winter. All of these viral infections are spread by:
Sneezing is an efficient method for dispersal, as a single sneeze can cause an expulsion of air traveling at initial velocities of over 200 miles per hour containing up to 100,000 droplets and 10 million virus particles. These droplets can end up in other people's mouths or noses, where they can cause infection. The droplets can also land on objects that people touch, utilize hand transfer from contaminated surfaces to eyes, nose or mouth providing access to mucous mambranes where they spread along the respiratory tract epithelium, mostly by cell to cell transfer. A recent discovery regarding the NCoV causing SARS-like infections is that it spreads more quickly between cells reaching its peak ability to replicate in 2 days instead of 4 days with SARS virus.
Survival in the Environment
CDC and other sources state that "80% of all infections are transmitted by hands, this includes all of the viruses of this group. All but rhinovirus and adenovirus posses lipid envelopes resulting in poor survival on hands but lasting long periods in the environment. RSV can persist for several hours on toys or other objects, which explains the high rate of nosocomial RSV infections, particularly in pediatric wards with up to 50% of the personnel in wards becoming infected during an outbreak. Viruses having lipid envelopes are easily inactivated by soap and water and alcohol sanitizer. Rhinovirus is the best survivor in this group and because of this, the majority of colds are transmitted by autoinoculation by contact with contaminated surfaces and then by touching eyes, nose or mouth.
Effective Hand Hygiene Measures
We are all capable of overcoming these pathogens using simple standard, contact, and airborne precautions including hand hygiene and surface disinfection. For influenza, respiratory syncytial virus (RSV), human parainfluenza virus, coronaviruses, metapneumovirus, adenovirus and rhinovirus, hand hygiene consisting of careful and frequent hand washing with soap and water is the first step to limit the spread and prevent infections.
If hands are not soiled, as a supplement to hand washing, alcoholic and chemical sanitizers are highly effective against enveloped viruses that act on the RNA core but first by disrupting the envelope. With rhinoviruses and adenoviruses, alcohol sanitizer while not quite as effective, still provide high kill rates (< 3 Log 10 reduction) when used to compliment hand washing.
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