Health Alerts > 9/3/09 Testing for H1N1
Topic: Testing for H1N1
Confirmatory Testing:
According to the latest CDC H1N1 influenza surveillance, 99% of circulating Influenza A virus is H1N1. Therefore, it is prudent to assume that patients who test positive for Influenza A on the rapid test have H1N1. There is no need to send patients who test positive for Influenza A for confirmatory testing for H1N1 by the Indiana State Department of Health as they are only accepting specimens that are post mortem or through their existing sentinel sites.
Confirmatory PCR testing is available as a sendout lab through the private sector. However, the test is approximately $300.00 plus handling fees and the patient must go the lab for specimen collection. Order H1N1 PCR test.
Rapid Influenza Testing
The Centers for Disease Control and Prevention (CDC) recently evaluated the performance of several rapid influenza diagnostic tests (RIDTs) that are commercially available. The results showed that, although the RIDTs were capable of detecting novel A (H1N1) virus from respiratory specimens containing high levels of virus, the overall sensitivity was low (40%--69%) among all specimens tested and declined substantially as virus levels decreased. These findings indicate that, although a positive RIDT result can be used in making treatment decisions, a negative result does not rule out infection with novel influenza A (H1N1) virus. Patients with illnesses compatible with novel influenza A (H1N1) virus infection but with negative RIDT results should be treated empirically based on the level of clinical suspicion, underlying medical conditions, severity of illness, and risk for complications. If a more definitive determination of infection with influenza virus is required, testing with rRT-PCR or virus isolation should be performed as described above, but the cost is significant and should only be done if it helps you in your diagnosis and treatment plan.
Summary
RIDT result: Positive for Influenza Type A
Note: This test can not distinguish influenza A virus subtypes. For example, this test cannot distinguish influenza infections caused by novel influenza A viruses versus seasonal influenza A viruses.
RIDT result: Negative for Influenza A and B
Note: The sensitivity of this assay has been shown to range between [10-70%*] for the detection of novel influenza A (H1N1) virus and between [20-100%*] for seasonal influenza viruses. A negative result does not exclude influenza virus infection. If influenza is circulating in your community, a diagnosis of influenza should be considered based on a patient’s clinical presentation and empiric antiviral treatment should be considered, if indicated. If more conclusive testing is desired, follow-up confirmatory testing with either [viral culture or RT-PCR*] is warranted.
Positive Influenza A results do not need to be faxed to our office. However, deaths due to Influenza do need to be reported.
Treatment
Treatment is recommended for:
All hospitalized patients with confirmed, probable or suspected novel influenza (H1N1).
Patients who are at higher risk for seasonal influenza complications.
If a patient is not in a high-risk group or is not hospitalized, healthcare providers should use clinical judgment to guide treatment decisions, and when evaluating children should be aware that the risk for severe complications from seasonal influenza among children younger than 5 years old is highest among children younger than 2 years old.
Post exposure antiviral chemoprophylaxis with either oseltamivir or zanamivir can be considered for the following:
Close contacts of cases who are at high-risk for complications of influenza
Health care personnel, public health workers, or first responders who have had a recognized, unprotected close contact exposure to a person with novel (H1N1) influenza virus infection (confirmed, probable, or suspected) during that person’s infectious period.
Questions for Parkview laboratory should be directed to
Dr. Craig McBride, Medical Director at Parkview Health Labs (260) 373-3656.
Questions for Lutheran and St. Joseph laboratory should be directed to Mary Shoaff 435-7165
Questions for Dupont Hospital Laboratory should be directed to Jason Amich at 435-7014
Thanks and for questions please feel free to call
Deb McMahan, MD
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