There is a sense of steadily building concern around avian influenza, remembering that an avian influenza outbreak would knock spots off COVID-19 (especially the modern variants) in terms of bad clinical outcomes. A letter in the NEJM relates wastewater surveillance in the state of Texas that has identified H5N1 avian influenza in all 10 cities in the surveillance programme since March 2024. This suggests that avian influenza is out there, and flying under the radar in animal populations. So, now would be a good time to dust down your pandemic influenza preparedness documents…

Whilst avian influenza is (no surprise!) usually a disease in poultry, there have been 14 human cases of H5N1 avian influenza in the USA this year in 3 US states. H5N1 influenza was not detected in wastewater before March 2024, and since then, it has been identified in all 22/23 sampling points from all 10 cities in the programme.

Commonly circulating strains of influenza (H3N2 and H1N1) are detected commonly in these wastewater samples, and correlate with clinical caseloads. For now, there is no direct correlation between prevalence of H5N1 in the wastewater and human infections, but there’s good reason to suspect that this may well change if H5N1 begins to transmit more efficiently between humans.

So, as the authors reflect, these are troubling findings. And may signal more cases of H5N1 avian influenza in humans in the near future.