Most patients with uncomplicated cases of influenzalike illness, including suspected pandemic influenza A(H1N1), do not need diagnostic testing as part of their clinical management, according to updated interim guidelines released by the Centers for Disease Control and Prevention.
“These recommendations also can be adapted according to local epidemiologic and surveillance data and other state and local considerations,” the CDC said.
The CDC recommends influenza diagnostic testing for:
▸ High-risk patients for whom a diagnosis will affect ongoing care, such as pregnant women or immunocompromised persons.
▸ Hospitalized patients. Those with suspected flu should be tested as soon as possible, but neither antiviral therapy nor infection control practices should be delayed while waiting for test results.
▸ Patients who have died from suspected or confirmed influenza.
For patients who are not severely ill or at high risk for complications, clinicians are advised to weigh whether diagnostic testing is needed to determine clinical care, infection control, or management of close contacts.
Tests available to detect flu viruses include rapid influenza diagnostic tests (RIDTs), direct immunofluorescence assays (DFAs), and real-time reverse transcriptase polymerase chain reaction tests (rRT-PCRs). When interpreting test results, consider the sensitivity of the test, the patient's stage of illness, and local virus surveillance information (www.cdc.gov/flu/weekly
When influenza viruses are circulating in a community, the positive predictive value of the RDIT and DFA tests are high, but they may not specifically identify the H1N1 subtype. And not all rRT-PCR assays can identify the 2009 H1N1 virus, according to the CDC statement.
If specific diagnosis of the 2009 H1N1 influenza virus is required, the CDC recommends testing with either an rRT-PCR assay specific for 2009 H1N1 influenza or testing with a viral culture.
The recommendations also include guidance for clinicians about proper collection and storage of respiratory specimens.
Find the complete recommendations online at the CDC Web site, www.cdc.gov