ATLANTA, Ga. — The Centers for Disease Control and Prevention (CDC) this month issued a health advisory for people "with close or prolonged unprotected contact with infected birds or contaminated environments" to be alert to the possibility of human infection from highly pathogenic avian influenza, or HPAI.

"While these recently-identified HPAI H5 viruses are not known to have caused disease in humans, their appearance in North American birds may increase the likelihood of human infection in the United States," stated a June 2 CDC Official Health Advisory.

It advised human infection with other avian influenza viruses, including a different HPAI (H5N1) virus found in Asia, Africa and other parts of the world, the HPAI (H5N6) virus and the H7N9 virus, has been associated with severe, sometimes fatal, disease. Previous human infections with other avian viruses have most often occurred after unprotected direct physical contact with infected birds or surfaces contaminated by avian influenza viruses, being in close proximity to infected birds or visiting a live poultry market.

"Human infection with avian influenza viruses has not occurred from eating properly cooked poultry or poultry products," the advisory stated – which the CDC has been saying since the first HPAI detections in December 2014. "CDC considers the risk to the general public from these newly-identified U.S. HPAI H5 viruses to be low.

"However, people with close or prolonged unprotected contact with infected birds or contaminated environments may be at greater risk of infection."

For now, the CDC’s public health recommendations are largely consistent with guidance for flu viruses associated with severe disease in humans. The agency considers these newly-identified HPAI H5 viruses as having the potential to cause severe disease in humans.

Clinicians should consider the possibility of HPAI H5 virus infection in people showing signs or symptoms of respiratory illness who have relevant exposure history. This includes people who have had contact with potentially infected birds (handling, slaughtering, defeathering, butchering, culling, preparation for consumption) or direct contact with surfaces contaminated with feces or parts (carcasses, internal organs, etc.) of potentially-infected birds, and those who have had prolonged exposure to potentially-infected birds in a confined space.

"People should avoid unprotected exposure to sick or dead birds, bird feces, litter or materials contaminated with suspected or confirmed HPAI H5 viruses," advised the CDC. "All recommended personal protective equipment (PPE) should be worn when in direct or close contact (within about 6 feet) with sick or dead poultry, poultry feces, litter or materials contaminated with suspected or confirmed HPAI H5 viruses."

The agency further recommended those exposed to HPAI H5-infected birds (including people wearing PPE) should be monitored for signs and symptoms consistent with influenza beginning after their first exposure and for 10 days after their last exposure. People who develop respiratory illness after exposure to HPAI H5-infected birds should be tested immediately for influenza by their state health department and be given the antiviral treatment.

To reduce their risk of infection, workers should also receive training on and demonstrate an understanding of when to use PPE; what PPE is necessary; how to properly put on, use, take off, properly dispose of and maintain PPE; and the limitations of PPE.

For additional guidance on worker protection, visit www.cdc.gov/flu/avianflu/h5/worker-protection-ppe.htm

According to the CDC, no human vaccines for HPAI are available in the United States. Efforts are under way to develop vaccines against H5 viruses. Seasonal influenza vaccines do not provide any protection against human infection with H5 viruses.