Amid H5N1, CDC Wants Faster Influenza A Subtyping for Hospitalized Cases

The CDC is now calling for subtyping of influenza A viruses in all hospitalized patients — and on an accelerated timeline, ideally within 24 hours.

Nirav Shah, MD, JD, principal deputy director of the CDC, said during a press briefing on Thursday that, currently, patients hospitalized with influenza receive a diagnosis from confirmatory testing “eventually,” and the new guidance will enable more rapid patient care, as well as better infection control measures for healthcare workers, by helping to prevent delays in identifying H5N1 infections.

“In short, the system right now tells us what has already happened,” Shah said. “What we need is to shift to a system that tells us what’s happening in the moment. That is what we are doing today.”

The agency also released a Health Alert Network (HAN) health advisory, recommending that clinicians take an exposure history from hospitalized patients with suspected or confirmed flu, including potential exposures to wild and domestic animals — including pets like cats — and animal products such as poultry, dairy products, raw cow milk, raw cow milk products, and raw meat-based pet foods.

It also recommends asking about recent close contact with a symptomatic person with a possible or confirmed case of H5N1.

Demetre Daskalakis, MD, MPH, director of CDC’s National Center for Immunization and Respiratory Diseases, also noted that people should be cautious about coming into contact with sick birds, particularly backyard flocks that are ill.

“We should be advising folks to try to prevent any unnecessary exposures to birds, especially if they are sick or dying,” he said during the briefing. “If you have sick or dying birds in the backyard … it’s important to alert public health as well as animal experts in your area.”

Shah noted that the CDC’s assessment of the current threat of H5N1 to public health remains low, and that the potential for this virus to cause a pandemic remains moderate. The agency also does not believe it is currently missing cases of H5N1 infection, he said.

However, the changes come in the context of a recent case of H5N1 in a child in San Francisco who had only conjunctivitis and a fever, didn’t require hospitalization, and fully recovered. That child had no clear exposure source identified, including any animals, and all of the child’s contacts were asymptomatic and negative for H5N1, Shah said.

This is the second confirmed infection in a child to date, and the fourth case of H5 picked up by national flu surveillance, he said. It’s on this background that the agency now recommends an acceleration of the subtyping process for patients hospitalized with influenza A.

Subtyping can help avoid delays in identifying H5N1 infections, which are more likely when seasonal flu activity is high, as it is now, according to the HAN. A test that is positive for influenza A but negative for seasonal flu subtypes H1 and H3 would indicate the presence of the H5 virus, it stated.

Doctors should use infection control measures if a hospitalized patient has suspected, probable, or confirmed H5N1, putting the patient in an airborne infection isolation room with negative pressure, and using standard, contact, and airborne precautions with eye protection such as goggles or a face shield.

Clinicians should use “whatever diagnostic test is most readily available” for the initial diagnosis, according to the CDC. Subtyping tests should be performed in the hospital clinical lab if possible. Otherwise they should be sent to a commercial clinical lab, or if that’s not available, a public health lab.

Any hospitalized patient, especially one in the intensive care unit, with suspected seasonal or H5N1 influenza should be started on antiviral treatment with oseltamivir (Tamiflu) as soon as possible without waiting for the results of testing, according to the guidance. Clinicians should consider combination antiviral treatment for hospitalized patients with H5 infection.

They should also notify public health officials as soon as possible if H5 is suspected, probable, or confirmed in a hospitalized patient, per the guidance.