Tuesday, October 18, 2016

UK PHE: Rounding Up The Usual Respiratory Virus Suspects

Credit UK PHE


Last Friday, in Colombian MOH: Increase In Child Deaths Due To ARI, myriad of respiratory infections - mostly (but not entirely) viral - that can cause severe illness, particularly in children.

While Influenza (A & B) get the most attention - partially because of their ability to cause serious morbidity and mortality - they are often overtaken by some of the other usual viral suspects. 

Today the UK's PHE has released a chart (see above) showing prevalence (based on laboratory surveillance) of the six top respiratory pathogens reported over the past dozen years.

As you'll see, RSV was the most commonly reported viral infection, followed by influenza, and then rhinovirus.


This graph shows the weekly distribution (using 3-week moving average method) of the number of samples positive for 6 major respiratory viruses, including:
  • influenza A
  • influenza B
  • RSV
  • rhinovirus
  • parainfluenza
  • adenovirus
These viruses were reported from Public Health England (PHE) and NHS laboratories voluntary surveillance database, the Second Generation Surveillance System (SGSS).

Information for England and Wales between weeks 1 of 2004 and 40 of 2016.

The UK's PHE describes RSV as:
Respiratory syncytial virus (RSV) is an enveloped RNA virus and is in the same family as the human parainfluenza viruses and mumps and measles viruses. RSV is one of the common viruses that cause coughs and colds in winter.

RSV usually causes mild respiratory infection in adults and children, but it can be severe in infants who are at increased risk of acute lower respiratory tract infection. RSV is the most common cause of bronchitis in children aged under 2 years.

Public Health England monitors levels of RSV activity in England and Wales and publishes information throughout the RSV season.

You'll notice the PHE chart depicts a sharp rise in the amplitude of influenza waves - beginning in 2009 - showing as much as a 20-fold increase in flu detections.

While some of this (particularly during the 2009-2010 pandemic) undoubtedly does represent an increase in the incidence of flu, changes in testing procedures, priorities, and the volume of samples tested over the years are probably bigger factors. 

There is a similar increase in rhinovirus and parainfluenza detections - starting in 2009 - which suggests increased surveillance, not increased incidence, is behind these hugely elevated numbers.

So, the ratio of viruses detected, rather than the volume reported, is the most telling part of this report.
Each year the CDC estimates that roughly 10% and 15% of the population will be infected with influenza. During the height of `flu season’, only between 25%-30% of the samples submitted by doctors to the CDC actually test positive for influenza.

The bottom line is that many people think they get the `flu' each year, when really they have one of the other viral suspects. And this is important from a public health standpoint for a couple of reasons.

First, since many of these milder respiratory viruses are commonly perceived by the public as being the `flu’, many people develop a false sense of what having real influenza can be like. 

And second, many who have gotten a flu shot and are subsequently sickened by one of these other circulating viruses, come away believing that the flu shot failed them.

Both have serious implications, as both tend to dissuade the public from getting the seasonal flu vaccine.  And that can cost lives.

Early reports suggest H3N2 may be the dominant flu strain circulating this winter. H3 viruses tend to be more severe than H1 seasons, particularly for the elderly and very young.

As I recently wrote in #NatlPrep: Giving Preparedness A Shot In The Arm, I elected to get my flu shot late last month.

While the vaccine can’t promise 100% protection, it – along with practicing good flu hygiene (washing hands, covering coughs, & staying home if sick) – remains your best strategy for avoiding the flu (and other viruses) this winter.

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