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Why There Won’t Be A Test At The End Of This Blog

 

 

# 3787

 

 

Despite numerous news stories to the contrary, many members of the public still expect that their doctor will test them to see if they have the H1N1 virus should they develop flu-like symptoms.


For most people, it seems a no-brainer.  After all, isn’t it important to know if it’s swine flu?


The answer today is far different than it was 5 months ago.  Today, if you’ve got the flu, you’ve probably got `swine flu’.  Somewhere around 98% of the positive virus samples tested are now novel H1N1.

 

Testing is still appropriate for those hospitalized with severe symptoms, and for some people in high risk groups, but for most people testing is a waste of time, money, and scarce resources.

 

The CDC released two guidance documents last night on this issue, one for the general public and one for clinicians. 

 

We’ll take a look at some excerpts from each.

 

Influenza Diagnostic Testing During the 2009-2010 Flu Season

September 29, 2009, 6:00 PM ET

For the Public

How will I know if I have the flu this season?

You may have the flu if you have one or more of these symptoms: fever, cough, sore throat, runny or stuffy nose, body aches, headache, chills, fatigue and sometimes, diarrhea and vomiting. Most people with 2009 H1N1 have had mild illness and have not needed medical care or antiviral drugs, and the same is true of seasonal flu. (More information is available on What To Do If You Get Sick this flu season.) Most people with flu symptoms do not need a test for 2009 H1N1 because the test results usually do not change how you are treated. 

<SNIP>

 

Will my health care provider test me for flu if I have flu-like symptoms?

Not necessarily. Your health care provider may diagnose you with flu based on your symptoms and their clinical judgment or they may choose to use an influenza diagnostic test. Depending on their clinical judgment and your symptoms, your healthcare provider will decide whether testing is needed and what type of test to perform. CDC has provided recommendations for clinicians this season to help with testing decisions. This season, most testing will be done in people who are seriously ill (hospitalized patients) and patients where testing may impact treatment decisions. In most cases, if a healthcare provider suspects you have the flu, the test results will not change their treatment decisions.

(Continue . . .) 

 

This next guidance document is directed toward clinicians.

 

Interim Recommendations for Clinical Use of Influenza Diagnostic Tests During the 2009-10 Influenza Season

September 29, 2009, 6:00 PM ET

Objective

To provide updated interim recommendations on influenza diagnostic testing for clinicians treating patients with suspected 2009 H1N1 influenza virus infection and to assist clinicians with testing decisions for the 2009-10 influenza season 1. These recommendations may be further revised as more information becomes available. These recommendations also can be adapted according to local epidemiologic and surveillance data and other state and local considerations.  Clinical judgment is always an important part of testing and treatment decisions.

Summary Points

  • Most patients with clinical illness consistent with uncomplicated influenza who reside in an area where influenza viruses are circulating do not require diagnostic influenza testing for clinical management.
  • Patients who should be considered for influenza diagnostic testing include:
    • Hospitalized patients with suspected influenza
    • Patients for whom a diagnosis of influenza will inform decisions regarding clinical care, infection control, or management of close contacts.
    • Patients who died of an acute illness in which influenza was suspected.

(Continue . . .)

 

 

Included in this guidance is the following chart which shows the four common types of influenza tests, their reliability (sensitivity), and the time it takes to process. 

image

 

Rapid influenza tests, the type that are commonly available in doctor’s offices and clinics, do a disappointing job identifying infection with this novel H1N1 virus. 

 

Detection rates run anywhere from an abysmal 10% to as high as 70%.   We’ve discussed the problems with these RIDTs (Rapid Influenza Diagnostic Tests) before:

 

No Doesn’t Always Mean No
Apples, Oranges, And Influenza Death Tolls
Lancet: Atypical H1N1 Presentation In Children
Japan: Rapid Influenza Test Sensitivity

 

Additionally, these tests don’t tell the doctor what strain of flu you have (although a positive for Influenza `A’ right now almost certainly means novel H1N1 swine flu).   So between an inability to differentiate between flu strains, and with an accuracy rating roughly as reliable as flipping a coin, these RIDTs are of limited value with this new flu strain.

 

Which is why doctors are being urged to diagnose influenza based primarily on clinical examination of the patient, and not to rely on rapid influenza tests.

 

Although the novel H1N1 swine flu appears poised to either supplant – or perhaps co-exist along side - our other seasonal flu strains, it will probably take awhile before the public grows comfortable enough with this new flu that they no longer expect routine testing.


Until then, expect this message to be repeated by the CDC and HHS on a regular basis.

Related Post:

Guidelines
H1N1
CDC

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