Avian influenza A (H5N1) — the highly pathogenic bird flu virus that has been circulating in U.S. dairy cattle herds since March 2024 — was detected in the wastewater systems of 10 Texas cities, including Houston, through a surveillance system jointly operated by researchers at UTHealth Houston and Baylor College of Medicine.
The finding, first published in the New England Journal of Medicine, was subsequently cited in June 2026, in connection with the continued monitoring of H5N1 activity in Texas through the TexWEB program. The research was part of the Texas Epidemic Public Health Institute (TEPHI), a surveillance infrastructure that collects wastewater samples weekly from 15 Texas cities and 40 sample sites — including Austin, Baytown, Brownsville, El Paso, Houston, Humble, Laredo, Lubbock, Missouri City, and Wichita Falls.
The data are stark: before March 2024, H5N1 had not been detected in 1,337 wastewater samples analyzed by the team. CIDRAP reported that from March 4 through July 15 of the detection period, H5N1 was found in 10 of 10 monitored cities, 22 of 23 monitored sites (96%), and 100 of 399 samples (25%). At some points, H5N1 became the dominant influenza serotype detected in Texas wastewater — a finding the NEJM authors called "troubling."
Crucially, the abundance of H5N1 sequences in wastewater did not correlate with influenza-related hospitalizations during the same period — indicating that the virus was reaching sewage primarily through animal waste from agricultural processing and livestock operations, not through widespread human infection.
What Wastewater Detection Means — and Why It Is an Important Signal
Wastewater surveillance does not mean H5N1 is actively spreading between humans. Harris County Public Health (HCPH) confirmed that no human cases of H5N1 had been reported in Harris County at the time of the initial detection and that the risk to the public was assessed as extremely low. The most likely sources of the virus in the wastewater were agricultural activities — specifically, the slaughtering and processing of poultry and the movement of cattle through facilities connected to municipal sewage systems.
Wastewater surveillance functions like an early warning system — capable of detecting the presence of a pathogen in a community before clinical cases are identified, before people seek healthcare, and before outbreaks are formally reported. As TEPHI describes its TexWEB network: the system uses advanced viral sequencing technology to detect thousands of viruses, including H5N1, from wastewater samples collected every week. It can find signs of viral activity in a community, potentially before they become visible in healthcare systems.
The NEJM authors recommended that findings like theirs should prompt expanded, agnostic wastewater sequencing alongside surveillance of livestock, agricultural products, and farm workers — as well as systematic monitoring of migrating birds along major flyways. Scientists are specifically watching for any genetic changes in the virus that could indicate adaptation toward more efficient human-to-human transmission — the scenario that would transform this from a farm-level outbreak into something requiring pandemic-level response.
| Wastewater H5N1 Detection Data | Detail |
| Cities with H5N1 detected | 10 of 10 monitored Texas cities |
| Sites with at least one detection | 22 of 23 sites (96%) |
| Samples positive | 100 of 399 total samples (25%) |
| Period of detection | March 4 – July 15 (detection study period) |
| Confirmed human cases in Houston area | None at time of detection |
| Correlation with hospitalizations | None — wastewater signal did not correlate with clinical cases |
| Primary suspected source | Agricultural processing and livestock operations |
| CDC confirmed U.S. human cases (total through May 2026) | At least 70 |
| Surveillance network | TexWEB (TEPHI / UTHealth Houston / Baylor College of Medicine) |
The Bigger Picture — H5N1 in the U.S. as of 2026
The TexWEB wastewater data should be understood in the context of the broader U.S. H5N1 situation. The CDC's surveillance page shows that from February 2022 through May 30, 2026, there have been at least 70 confirmed human H5N1 infections in the United States — all in individuals with direct, unprotected exposure to infected animals, primarily dairy farm workers and poultry workers. No sustained human-to-human transmission has been detected.
However, infectious disease experts and epidemiologists have noted that the true number of human infections may be significantly higher than the confirmed count suggests. Serological surveys of dairy workers in affected states have, in some studies, found evidence of prior H5N1 infection in workers who never sought care or reported symptoms. The combination of frequent mild or asymptomatic infection, reluctance among some agricultural workers to report illness, and the logistical difficulty of surveilling a rural, mobile workforce may mean that official case counts understate actual exposure levels.
For the average Houston resident or World Cup visitor, the risk of contracting H5N1 today remains low. The CDC maintains that H5N1 does not spread efficiently between humans, and there is no evidence of sustained human-to-human transmission. However, public health infrastructure decisions — including surveillance funding, agricultural worker health monitoring, and wastewater testing capacity — directly determine how early the next outbreak is identified, whatever form it takes.
The public health advice from HCPH and the CDC is clear: avoid exposure to animal waste, bedding, or materials from birds or animals suspected of H5N1 infection. Do not drink raw milk — pasteurization kills H5N1 viruses. Farm workers with direct animal exposure should use appropriate PPE as recommended by the CDC. Report any unexplained respiratory illness or eye infection to a healthcare provider if you have had recent contact with birds or cattle.
Frequently Asked Questions
Does H5N1 in wastewater mean it is spreading between humans in Houston?
No. CIDRAP and Harris County Public Health confirmed that the wastewater detection did not correlate with influenza-related hospitalizations, and no human H5N1 cases were reported in Harris County at the time. The most likely source of the virus in the wastewater is agricultural processing — cattle slaughter facilities and poultry processing plants connected to municipal sewage.
What is TexWEB, and how does it detect H5N1?
TexWEB (Texas Wastewater Environmental and Biomonitoring program) is an advanced surveillance network operated by TEPHI, UTHealth Houston, and Baylor College of Medicine that collects wastewater samples weekly from 15 Texas cities and 40 sites. It uses whole-virome sequencing technology to detect thousands of viruses — including H5N1 — in wastewater before those viruses appear in clinical case reports.
How many human H5N1 cases have been confirmed in the U.S.?
The CDC reported at least 70 confirmed human H5N1 infections in the United States between February 2022 and May 30, 2026. All confirmed cases involved direct, unprotected exposure to infected animals, primarily dairy workers and poultry workers. No sustained human-to-human transmission has been detected.
Is the food supply safe from H5N1?
Yes. The CDC and USDA state that pasteurized dairy products are safe — pasteurization kills H5N1 viruses. Properly cooked poultry and eggs (internal temperature of 165°F) also eliminate H5N1. Raw milk carries risk and should be avoided. Well-cooked meat from properly inspected sources is considered safe.
What should the public do given these findings?
Avoid contact with sick or dead birds and livestock. Do not drink raw milk. Farm workers with direct animal exposure should use CDC-recommended protective equipment. Anyone who develops unexplained fever, respiratory illness, or eye infection within 10 days of contact with birds or cattle should contact a healthcare provider and disclose the exposure. For current H5N1 situation updates, visit the CDC's A(H5) Bird Flu monitoring page.
