# 4187
After hearing repeatedly that nearly 100% of all positive flu samples over the last six months have been the novel H1N1 virus, you might come away believing if you’ve had a flu-like illness you’ve had the pandemic virus.
The problem is, a crucial piece of information is missing; What percent of all samples tested positive for influenza?
And here, the answer may be surprising.
At its height, during the pandemic wave back in late October, the percentage of samples from people with ILI’s (Influenza-like illnesses) submitted to the CDC that tested positive for influenza (any type) was under 40%.
You see, there are a plethora of respiratory pathogens that circulate year-round, and influenza makes up but a small percentage of them.
Some of the `usual suspects’ would include metapneumovirus, parainfluenzavirus, respiratory syncytial virus (RSV), adenovirus, or any of the myriad Rhinoviruses (Common cold).
Back in October, I looked at some of these other viruses in a blog entitled:
Tuesday, October 13, 2009
ILI’s Aren’t Always The Flu
# 3832
Although nearly all of the influenza circulating in the the US and Canada right now is apparently the novel H1N1 `swine’ flu, it would be incorrect to say that if you have a flu-like illness, you must have the pandemic flu.
Last week’s numbers from the CDC’s FluView, which I’ve plugged into the above spreadsheet so as to generate a graph, show that more than 72% – almost 3/4ths – of all virus samples tested from people who had flu-like symptoms came back negative for influenza.
For the latest reporting week (49), the CDC is showing just under 7% of the viruses sampled testing positive for the H1N1 virus. Even though nearly 100% of the influenza detected has been H1N1.
Last night Maggie Fox, Reuter’s Health and Science Editor, brought us details of some new analysis of the other 94% of the viruses being tested in the US.
Maggie is one of the best reporters in the business, and her work is always worth reading it in its entirety.
Other viruses abound in U.S. flu season, tests show
Maggie Fox, Health and Science Editor
WASHINGTON
Tue Dec 22, 2009 5:29pm EST
WASHINGTON (Reuters) - Several flu-like viruses are more common than usual this flu season in the United States, adding to the misery and confusion caused by H1N1 swine flu, one lab company said on Tuesday.
Kansas City, Missouri-based ViraCor Laboratories found that only 6 percent of the samples it was sent tested positive for influenza A virus. Tests by the U.S. Centers for Disease Control and Prevention show virtually all influenza now circulating is H1N1 swine flu.
The rest include a range of flu-like viruses, each caused by a distinct germ but all causing similar symptoms.
By far the most common is rhinovirus, one of the so-called common cold viruses, the testing company found.
This fits in with a report last November from Children's Hospital of Philadelphia, where 500 children were hospitalized with rhinovirus in September and October -- an unusually high number to be that sick with a normally mild virus.
In mid-November, in a blog entitled When The `Flu’ Isn’t The Flu, I wrote about the discovery at the Children’s Hospital of Philadelphia of an unusually virulent (and possibly new) rhinovirus – essentially a common cold – that began hitting some children hard earlier this fall.
Once again, we turn to Maggie Fox for the details, in her article from a little over a month ago.
Not just swine flu - new cold virus may lurk, too
Tue Nov 17, 2009 3:24pm EST
By Maggie Fox, Health and Science Editor
WASHINGTON (Reuters) - Runny nose, fever, cough, even pneumonia -- the symptoms sound like swine flu but children hospitalized at one U.S. hospital in fact had a rhinovirus, better known as a common cold virus, doctors said on Tuesday.
Hundreds of children treated at Children's Hospital of Philadelphia had a rhinovirus, and federal health investigators are trying to find out if it was a new strain, and if this is going on elsewhere in the country.
All of this means that if you’ve had an ILI in recent weeks there is a pretty good chance it was something other than novel H1N1.
Doctors don’t generally test for anything beyond influenza when a patient comes in with a flu-like illness because the tests are expensive and the results aren’t generally available until after the virus has run its course.
In other words, they have very little bearing on treating a patient.
Surveillance and testing do have value from an epidemiological standpoint, however. And so this data is of great interest to scientists, and to doctors, who use it to decide how prevalent various viruses are in their community.
If you’ve put off getting the H1N1 vaccine because you believe you’ve already had the virus, you might want to reconsider that decision.
You may have had something else entirely, and may not have immunity you might think you do.
While many people who contract the H1N1 virus have a mild course of illness, not every `mild flu’ over the past 6 months has been due to the pandemic virus.
Something to bear in mind when someone recounts how mild the `pandemic virus’ was for them. They may not realize it, but they may have had nothing more than a nasty cold.
