#18,389
Over the spring and summer we've seen - for the very first time - evidence of the HPAI H5 influenza virus in samples taken from wastewater treatment plants from a number of U.S. states; mostly where there have been reports of HPAI in cattle.
A few past blogs include:
NEJM: Sequencing-Based Detection of Avian Influenza A(H5N1) Virus in Wastewater in Ten Cities
WastewaterSCAN Dashboard Now Tracking Influenza H5
EnvSciTech: Detection Of H5 HA In Municipal Wastewater Solids With Increases in Influenza A in Spring, 2024
FIGURE. Influenza A virus and H5 subtype testing in wastewater and sites with high levels* of influenza A virus or H5 detections reported to CDC — United States, May 12–July 13, 2024†
Given anecdotal reports of symptomatic farm workers refusing to be tested, sporadic (undetected) human infections can't be ruled out - but there other other plausible explanations - including the dumping of contaminated animals products, bird droppings, and other animal sources.
First, the press release from L.A. County, after which I'll return with more on the difficulties of detecting sporadic cases in the community.For Immediate Release:
November 01, 2024
The Los Angeles County Department is investigating possible sources of H5 avian flu, which has been detected at low levels for the first time at one of the wastewater sampling sites in Los Angeles County.
H5N1 is one type of avian influenza that has been spreading among birds and mammals, leading to a nationwide outbreak. There are no reports of human H5N1 cases in Los Angeles County and the overall risk of H5N1 to LA County residents remains low. There is no evidence of sustained human to human transmission with this strain of H5N1.
Public Health is actively engaging key risk groups such as dairy and meat processing sites to identify possible sources of H5 avian flu in wastewater. The virus may have been introduced into wastewater by discarded contaminated animal products, infected wild bird droppings entering the sewage system, or animal infection. Public Health routinely monitors and tests symptomatic birds, pets, and wild mammals in LA County for H5N1 through our Public Health Laboratory.
Wastewater sampling is routinely performed as part of ongoing surveillance for infectious diseases including H5N1. H5 has previously been detected in wastewater in both northern and southern California. The virus has been detected in more than 200 dairies in California and there have been 16 human cases of avian flu in California. Public Health, in conjunction with the California Department of Public Health (CDPH), the Centers for Disease Control and Prevention (CDC) and state and federal agriculture agencies, has been tracking the situation closely.
While the current risk of transmission to LA County residents is low, Public Health encourages residents to follow these best practices when around animals or when consuming animal products:
Do not eat raw milk, raw cheese, and undercooked meat products.
Avoid unprotected contact with sick or dead animals, or materials contaminated with bird feces. The virus can spread to other birds, pets or mammals by contact with infected feces or consumption of infected animals.
Avoid handling wild birds and observe them only from a distance. If you have to handle wild birds, even if they appear healthy, practice good hand hygiene and consider wearing a well-fitting mask. Some birds may carry the virus but appear to be healthy.
Report sick or dead birds to local animal control agency for potential collection and testing. Sick birds or animals may not have flu-like symptoms, but instead may be unable to fly, have seizures, have difficulty walking or be found dead.
Prevent wild birds from getting into areas housing pet birds or poultry. Also make sure wild birds cannot defecate down into areas holding pet birds or poultry.
Take down bird feeders and communal bird baths to reduce the risk of the virus spreading from bird-to-bird.
Residents should also keep pets away from sick and dead birds. There is some risk of the virus being transmitted to mammals such as dogs, cats, and wild mammals, especially if they eat infected, uncooked birds.
It is especially important that people who may have exposure to infected or potentially infected birds or other animals get a seasonal flu vaccine. Seasonal flu vaccination will not prevent infection with avian influenza viruses but can reduce the risk of getting sick with human and bird flu viruses at the same time.
About H5N1
Avian flu refers to various strains of influenza A viruses that typically infect birds. While these viruses mainly affect wild birds, sometimes they also infect other animals, including wild and domestic animals (including seals, foxes, cats, and cows). H5N1 is one type of avian influenza that has been spreading among birds and mammals, leading to a nationwide outbreak. This is the first time these bird flu viruses have been found to be spreading in cows.
Signs/symptoms of H5N1 virus infection in humans may include:
Cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue
Fever* or feeling febrile
Eye redness (or conjunctivitis)
Shortness of breath or difficulty breathing
Diarrhea, nausea, vomiting
*It is important to note that infection with influenza viruses, including novel influenza A viruses, does not always cause fever. Fever may not occur in infected persons of any age, particularly in persons aged 65 years and older or people with immunosuppression.
For questions or to find a nearby clinic or doctor, residents can call the Public Health InfoLine at 833-540-0473. Open every day from 8 a.m. to 8 p.m.
For more information, visit our websites:
Avian flu in animals: publichealth.lacounty.gov/vet/HPAI.htm
While an animal source may be responsible for the wastewater results in L.A., we know with any infectious disease that surveillance and testing can only pick up a fraction of the total number of cases.
The proverbial `tip of the iceberg’ or in the case of the CDC graphic below, the `top of the pyramid’.
Often, detection is a matter of luck. Last August a patient was briefly hospitalized in Missouri and more than a week after the patient was discharged, their respiratory sample tested positive for influenza H5.
Serological testing of close contacts revealed that a housemate may also have been infected (see CDC: Serology Results On Missouri H5 Patient's Contacts (Updated)), although only 1 of 3 tests was positive.
Had this patient not been hospitalized, neither of these cases would likely have been detected. Since many novel flu infections (both swine & avian) can present with mild or moderate symptoms, it is all but certain that some number go unreported.
UK Novel Flu Surveillance: Quantifying TTD
ECDC: Surveillance & Targeted Testing for the Early Detection of Zoonotic Influenza in Humans During the Winter Period in the EU/EEA
Lancet: Clinical Severity Of Human H7N9 Infection
CID Journal: Estimates Of Human Infection From H3N2v (Jul 2011-Apr 2012)
