CDC Releases New H7N9 Testing Recommendations

Troy Brown

June 11, 2013

Only patients who meet specific exposure criteria and have respiratory illness severe enough to require hospitalization should be tested for H7N9 influenza, according to a June 7 Health Update from the Centers for Disease Control and Prevention (CDC).

The update also directs practitioners to report only confirmed and probable cases of human infection with H7N9 to the CDC.

Previous recommendations on April 5 directed testing of all patients with relevant exposure and influenza-like illness, regardless of illness severity. The changes in testing recommendations are the result of the current epidemiology of H7N9, which has shown that most infections have caused severe illness, and only rarely mild illness. The World Health Organization has released similar recommendations.

As of June 3, more than 130 cases of human infection with H7N9 had been reported in mainland China and Taiwan. Most patients reported poultry contact before becoming ill and were hospitalized with severe respiratory illness. H7N9 has not resulted in widespread mild disease in China.

Several clusters of human infection with H7N9 have occurred in China, but sustained person-to-person transmission has not occurred there. No human cases of H7N9 have been identified in the United States in more than 60 persons who were tested when they developed respiratory symptoms after recent travel to China.

Clinicians should report confirmed and probable cases of human H7N9 infection in the United States to the CDC within 24 hours of initial identification. State health departments also are urged to investigate all suspected cases.

Interim Recommendations

  • Clinicians should consider H7N9 testing by reverse-transcription polymerase chain reaction for patients who meet both the clinical and exposure criteria described in these guidelines. Clinicians should test additional persons in whom H7N9 infection is suspected.

    • Clinical Illness Criteria

      1. patients with new onset of acute respiratory infection that is severe enough to require hospitalization, and

      2. patients without identification of an alternative infectious etiology.

    • Exposure Criteria

      1. patients who have travelled to areas (within 10 days of symptom onset) with known human cases of H7N9 infection or to areas where avian influenza A (H7N9) viruses are circulating in animals, or

      2. patients who have had close contact (within 10 days of symptom onset) with confirmed human cases of H7N9 infection.

  • In cases in which human H7N9 infection is suspected on the basis of current screening recommendations by public health authorities, respiratory specimens should be collected using infection precautions for novel virulent influenza viruses. The swab or aspirate should be placed in viral transport medium, and the state or local health department should be contacted to arrange transport to the appropriate health department for testing. Viral culture should not be performed in these cases. More information on diagnostic testing can be found on the CDC's Web site.

  • Rapid influenza diagnostic tests may not identify H7N9 in respiratory specimens, and a negative test result does not exclude H7N9 infection. In addition, a positive test result for influenza A is unable to distinguish between influenza A virus subtypes (human influenza A viruses vs novel influenza viruses), so it cannot confirm avian influenza virus infection. Respiratory specimens should be obtained and sent for reverse-transcription polymerase chain reaction testing at a state public health laboratory when rapid influenza diagnostic tests are positive for influenza in patients suspected of having novel influenza A virus infection. Do not base clinical treatment decisions on a negative rapid influenza diagnostic test result because the test is only moderately sensitive.

Infection Control

Information on infection control precautions for H7N9 can be found on the CDC Web site.

Treatment

Guidance on the use of antiviral medications in patients with suspected H7N9, and antiviral chemoprophylaxis of exposed contacts can be found on the CDC Web site.

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