Hawaii health officials investigate H5 signal in Oahu wastewater; public risk remains low

Hawaii health officials said Wednesday that a routine wastewater sample collected Nov. 7, 2024, on Oahu produced an H5 avian influenza signal and prompted an investigation, but they emphasized there are no reported human or animal H5N1 cases in the state and the immediate risk to the general public is low.

"There are no reports of human or animal H5N1 cases in Hawaii at this time," said Dr. Sarah Campbell, Hawaii state epidemiologist, at a news briefing announcing the detection and describing follow-up steps.

The Department of Health (DOH) said the flagged sample came from a wastewater treatment plant on Oahu and was identified through routine testing conducted by the Centers for Disease Control and Prevention's National Wastewater Surveillance System (NWS). DOH received and announced the result on Nov. 12. Campbell said wastewater testing can detect the H5 hemagglutinin antigen family but cannot by itself determine whether the signal represents the H5N1 subtype; additional testing and repeated detections would be needed for greater specificity.

"The wastewater testing provides a signal for further investigation to determine whether this detection is H5N1 related," Campbell said. She added that the state lab can attempt more specific testing if additional samples show the signal, but that such follow-up depends on sample quality and viral concentration.

Officials said possible sources for an H5 signal include wild birds migrating from areas with infection, people who traveled to affected areas and returned while infected (including asymptomatic cases), or agricultural products, though strict controls on agricultural imports make direct introduction via livestock less likely. Campbell noted that raw milk can carry high concentrations of the virus and that, while pasteurization makes milk safe to drink, in theory some viral material might still be detectable in wastewater.

Campbell urged residents to avoid touching sick or dead birds with bare hands and to report unusual die-offs or multiple sick animals. She provided Department of Agriculture contacts for reporting: (808) 483-7106 (Monday–Friday, 7:45 a.m.–4:30 p.m.) and (808) 837-8092 (after hours and holidays). People who develop fever, cough, sore throat or conjunctivitis after close contact with sick or dead animals should contact DOH at (808) 586-4586, she said. Antiviral treatment for influenza is available and recommended promptly for suspected cases.

The state stressed that the highest-priority groups for outreach are farm workers and others with direct animal exposure. "The people that we would focus the most on with such a detection are our farm workers," Campbell said, noting those workers need education on protecting themselves and animals and on biosecurity measures for farms.

DOH said it has collected additional wastewater samples from the same treatment plant and from other sites to check for persistent detection; wastewater sampling at the site is collected twice weekly and results typically take about a week. If repeated detections occur, the department will work with federal agricultural and wildlife partners to investigate sources and, as needed, reinforce biosecurity on poultry farms and related settings.

Campbell said the U.S. has seen H5 viruses spread among birds and some mammals on the mainland, and that human cases there have been reported mainly among people working closely with infected animals. "There's no evidence of sustained human-to-human transmission of H5N1 in the United States," she said, and the illnesses observed in exposed workers have been mild to date. However, she warned that the public-health goal is to minimize exposures in case the virus evolves.

On vaccines, Campbell said the CDC has done preparatory work that would make development of an H5N1 vaccine possible if needed, but there is currently no H5N1 vaccine in production. She encouraged seasonal flu vaccination to reduce the chance of co-infection and potential viral mixing.

DOH said it will update the public as further testing and investigation provide new information. For now, officials recommend reporting unusual animal illness or die-offs, using personal protective equipment when handling animals, and contacting DOH or the Department of Agriculture with questions or reports.