Diagnosing H1N1

How Your Health Care Provider May Diagnose H1N1

What happens when you are diagnosed with H1N1?. Jani Bryson/Vetta/Getty Images

Many people say that they have been diagnosed with 2009 novel H1N1, but they aren't actually ever tested for the illness, so we don't know for sure that they actually have it. This leaves a lot of people confused about how H1N1 is diagnosed.

At the beginning of the outbreak, the CDC and other public health agencies were tracking every case of swine flu. However, once it became a pandemic and it appeared the virus was not as serious as initially feared, they stopped tracking it so closely.

When the virus became so widespread, the criteria for diagnosing it changed quite a bit. Instead of requiring a test to be done and sent to a specialized lab, health care providers were instead able to diagnose H1N1 based on symptoms.

Criteria for Diagnosing H1N1 

According to the CDC, in areas where H1N1 is widespread, people can be diagnosed with the virus based on their symptoms. The primary symptoms doctors look for are a fever and a cough or a fever and a sore throat.

This does not mean that everyone who has H1N1 will have these symptoms, or vice versa. These are considered criteria for what is called "influenza-like illness" which could indeed be 2009 H1N1 influenza A. But, a patient with an ILI could have another strain of influenza, or another viral or bacterial illness all together.

More about H1N1 Symptoms

Diagnosis by Testing

Considering all this, a diagnosis may seem -- on the surface -- a bit arbitrary.

Some health care providers will use rapid flu tests to diagnose the flu. These tests are done in the office with a simple nasal swab and provide results in a matter of minutes. Some have the ability to differentiate between influenza A and B, but they cannot specifically identify pandemic H1N1. Rapid tests may also miss many flu cases.

So, doctors have to make decisions about treatment based on the possibility of 2009 H1N1 infection and your health status (whether or not you are in a high-risk group). For example, if you don't have the common symptoms mentioned above but H1N1 is widespread in your area, your doctor may still come to the conclusion that you have the virus. Doctors may make a diagnosis and treat with Tamiflu in high-risk patients. In short, "better to be safe."

More specific tests that can positively identify the H1N1 virus can be performed by specialized laboratories. 


"2009-2010 Influenza Season Triage Algorithm for Adults (older than 18 years of age) With Influenza-Like Illness." H1N1 Flu 27 Oct 09. Centers for Disease Control and Prevention. 19 Nov 09.

"Interim Guidance for Clinicians on Identifying and Caring for Patients with Swine-origin Influenza A (H1N1) Virus Infection." H1N1 Flu 04 May 09. Centers for Disease Control and Prevention. 19 Nov 09.

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