CDC updates advice on avian flu testing, lab work

Jun 8, 2006 (CIDRAP News) – The US Centers for Disease Control and Prevention (CDC) yesterday released updated guidelines that provide more details on when to test a patient for the H5N1 avian influenza virus, as well as substantially more specifics on laboratory testing.

In the revised guidelines, the CDC also recommends that H5N1 avian flu surveillance in the United States remain the same, saying the epidemiology of human cases has not changed significantly since the agency issued recommendations on surveillance in February 2004. The guidelines are titled "Updated Interim Guidance for Laboratory Testing of Persons with Suspected Infection with Avian Influenza A (H5N1) Virus in the United States" (see link below).

The new guidelines recommend lab testing for a patient whose illness is associated with all of the following: (1) hospitalization or death; (2) a fever of 38°C (100.4°F) or higher; (3) radiographically confirmed pneumonia, acute respiratory distress syndrome, or other severe respiratory illness; and (4) potential exposure within 10 days of symptom onset.

The CDC lists potential exposure as any of the following:

  • History of travel to a country with documented H5N1 in poultry, wild birds, or people and, during travel, at least one potential exposure (eg, contact with sick or dead domestic poultry, consumption of incompletely cooked poultry, or close contact with a person who was hospitalized  with a severe, unexplained respiratory illness)
  • Close contact (within about 3 feet) of a sick person who was confirmed or suspected to have H5N1
  • Working with live influenza H5N1 in a laboratory

In addition, the new guidelines recommend considering testing for a patient with: (1) mild or atypical disease (eg, respiratory illness and fever that does not require hospitalization, or significant neurologic or gastrointestinal symptoms in the absence of respiratory disease) and one of the exposures in the bulleted list above, or (2) severe or fatal respiratory disease whose epidemiologic information is uncertain, unavailable, or otherwise suspicious.

The new guidelines expand substantially on previous CDC guidelines, which called for testing for patients who have the radiographically confirmed severe respiratory illnesses listed above as well as a history of travel to a country where H5N1 infection has been documented. The previous guidelines called for considering testing for patients who have the same degree of fever listed above, as well as a cough, sore throat, or shortness of breath, and a history of contact with poultry or a known or suspected human case of H5N1 in an H5N1-affected country within 10 days of symptom onset.

The CDC update issued yesterday also provides greatly expanded recommendations for specimen collection and testing. They are condensed here:

  • Oropharyngeal swab specimens and lower respiratory tract specimens (eg, bronchoalveolar lavage or tracheal aspirates) are preferred over nasal or nasopharyngeal swab specimens.
  • Detection of H5N1 is more likely from specimens collected within 3 days of illness onset.
  • Bronchoalveolar lavage is a high-risk, aerosol-generating procedure that requires infection-control precautions such as gloves, gown, goggles, and fit-tested respirator.
  • Swabs used to collect specimens should have a Dacron tip and an aluminum or plastic shaft.
  • Influenza H5N1-specific reverse-transcriptase polymerase chain reaction (RT-PCR) testing conducted under biosafety level 2 conditions is the preferred diagnostic method.
  • For RT-PCR analysis, nucleic acid extraction lysis buffer can be added, after which specimens can be stored and shipped at 4°C (40°F) or properly deep frozen and shipped on dry ice.
  • Viral culture should not be attempted unless conducted under biosafety level 3 conditions.
  • Commercial rapid influenza antigen testing should be interpreted with caution for H5N1.
  • Serologic testing for influenza H5N1-specific antibody can be considered if other H5N1 diagnostic testing methods are unsuccessful.

The CDC update also reiterates that the public need not avoid travel to countries affected by H5N1. However, its advice remains that travelers to these countries should avoid poultry farms, bird markets, and other places where poultry is kept.

The agency also says that no evidence of reassortment between avian and human flu viruses has been found. However, the update states, "It is expected that human infections resulting from direct contact with infected poultry will continue to occur in affected countries." It adds, "This expanding epizootic continues to pose an important and growing public health threat."

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