Laboratory Tests Help Confirm Swine Flu Cases

With an increasing number of Swine influenza cases in North America, the Centers for Disease Control and Prevention (CDC) is advising doctors and other health care providers to consider the disease as a possible diagnosis in patients who present with flu-like signs and symptoms such as fever, chills, cough, sore throat, body aches, nausea and vomiting, especially in areas with confirmed cases. There are two types of influenza viruses (flu), A and B, which can cause severe respiratory illness. Swine influenza (Swine flu) is caused by a specific type (subtype) of influenza A virus known as H1N1.

To confirm suspected cases of flu, doctors may obtain a sample from the respiratory tract. The preferred sample is a swab of the very back of the nasal passages (nasopharyngeal or NP swab) or a wash of the nasal passages, which is obtained by pushing a small amount of sterile saline into the nose and then either applying gentle suction or using gravity to collect the resulting fluid (saline and mucus) into a cup. Click here for the CDC’s detailed information and most current recommendations on sample collection and processing.

In patients with appropriate clinical symptoms, samples should first be tested to detect the presence of influenza virus. If the initial flu test is positive for influenza A, another test is run to establish the virus subtype. Currently, the laboratory performing the initial test will send the sample to their state Public Health Laboratory or the CDC to perform tests that detect the swine-origin H1N1 virus. See the CDC factsheet (PDF) for more on Swine flu testing.

Timely diagnosis of cases of Swine influenza allows for early treatment with antiviral drugs such as Tamiflu and Relenza, which are currently known to be effective against the strain of virus causing recent Swine influenza infections. If given within 48 hours after symptoms first appear, the drugs may help lessen the severity of symptoms and decrease the risk of complications such as pneumonia. Early diagnosis also helps to control the spread of the disease by identifying those who are infected as soon as possible so they can limit their exposure to others. In addition to confirmed cases of Swine flu, treatment may be recommended for others who are waiting for test results and/or who may have been exposed. For the latest information on treatment recommendations, click here.

If you become ill with symptoms of the flu and live in an area with confirmed cases of Swine influenza, you may want to contact your doctor, who can help decide whether testing and treatment is necessary, advises the CDC.

For further information and daily updates on the status of Swine influenza cases in the United States, visit the CDC website.

Sources

(April 28, 2009) Centers for Disease Control and Prevention. Swine Flu, Guidance for Clinicians & Public Health Professionals. Available online at http://www.cdc.gov/swineflu/guidance/. Accessed April 28, 2009.

(April 24, 2009) Centers for Disease Control and Prevention. Key Facts about Swine Influenza. Available online at http://www.cdc.gov/swineflu/key_facts.htm. Accessed April 28, 2009.

Tests: Influenza Tests

Centers for Disease Control and Prevention (CDC): H1N1 Flu (Swine Flu)
CDC: H1N1 Flu (Swine Flu) and You