CDC issues guidelines for avian influenza H7N9 testing, specimen collection and sample processing in the US
To date, there has been a total of 132 laboratory-confirmed cases of human infection with avian influenza A(H7N9) virus reported to the World Health Organization (WHO) since the outbreak began–131 cases in China and one in Taiwan.
Human infection appears to be related to exposure to live poultry or contaminated environments. However,much remains unknown about this virus, including the animal reservoir(s) in which it is circulating, the main exposures and routes of transmission, and the scope of the spread of this virus among people and animals. Investigations are ongoing.
Although there has been no cases of human infection with the virus in the United States, the Centers for Disease Control and Prevention (CDC) has provided interim guidance for clinicians and public health professionals on appropriate specimen collection, storage, processing, and testing for patients who may be infected with avian influenza A (H7N9) virus.
The CDC says since there currently is no data describing prolonged shedding of infected individuals with this virus, the estimated duration of viral shedding is based upon seasonal influenza virus infection.
Specimen collection for avian influenza A (H7N9) virus testing should be as soon as possible after illness onset, ideally within 7 days of illness onset.
The specimens of choice include a nasopharyngeal swab, or a nasal aspirate or wash, or two swabs combined into one viral transport media vial (e.g., combined nasal swab with oropharyngeal swab or combined nasopharyngeal swab with oropharyngeal swab).
An acceptable alternative would be a single nasal swab or single oropharyngeal swab.
If the case is a lower respiratory infection, an endotracheal aspirate or bronchoalveolar lavage is preferred.
In addition, the CDC has specific requirements on types of swabs used and shipping requirements.
Concerning diagnostic testing, the CDC notes that the performance of current Food and Drug Administration (FDA) cleared diagnostic tests for influenza has been demonstrated for seasonal human influenza viruses as described by the manufacturer package insert. Performance has not been demonstrated with novel influenza A viruses.
Molecular assays may detect novel influenza A viruses, but will not differentiate novel influenza A viruses from seasonal influenza A viruses. For these assays a novel influenza A virus may give an influenza A “unsubtypable” result.
Rapid influenza diagnostic tests (RIDTs) and immunofluorescence tests also have unknown sensitivity and specificity to detect human infection with avian influenza A (H7N9) virus in clinical specimens.
The federal health agency says specimens to be tested for avian influenza A (H7N9) virus should be sent first to public health laboratories.
All state public health laboratories should use the CDC Human Influenza Real-Time RT-PCR Diagnostic Panel to screen specimens for InfA, InfB, and RP.
Health departments should test all InfA-positive specimens with the CDC Influenza A Subtyping kit using all primer/probe sets: H1, H3, pdmInfA, and pdmH1. Avian influenza A (H7N9) viruses will be positive for the influenza A target, but negative for the seasonal influenza A (H3) target, negative for the seasonal influenza A (H1) target, negative for the pandemic 2009 (pdmH1) target, and negative for the nucleoprotein (NP) gene target (pdmInfA) using the CDC Human Influenza Real-Time RT-PCR Diagnostic Panel. Public Health officials should contact CDC immediately if they obtain unsubtypable results when testing an influenza specimen.
Laboratories should not attempt diagnosis of patients who may be infected with avian influenza A (H7N9) virus using viral culture.
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