The US has ramped up influenza surveillance amid an ongoing outbreak of the bird flu virus H5N1 in dairy cattle. Public health officials hope more robust monitoring will help catch and contain any potential human outbreaks. But experts warn that without more surveillance, cases will slip through the cracks 鈥� if they haven鈥檛 already 鈥� which raises the risk of the virus spurring a pandemic in people.
Since 2003, roughly worldwide聽are reported to have had H5N1, around half of whom died of the infection. In 2021, a highly contagious version of H5N1 broke out in wild and domestic birds, killing tens of millions of them. This March, H5N1 was also found circulating among US dairy cows and has so far infected 281 herds across . While this version聽of the virus does not appear to transmit between people, just a few mutations could change that.
That is why an ongoing outbreak of H5N1 in US dairy cows is so alarming: when the virus infects a cow, it has an opportunity to become better at infecting mammals 鈥� humans included. It also puts the virus in close proximity to people. 鈥淎ll of those things are not good in terms of a virus that has that pandemic potential,鈥� said at Johns Hopkins University in Maryland during a news conference on 2 October.
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This year, 16 people in the US have tested positive for the virus, including two cases in California that the US Centers for Disease Control and Prevention (CDC) announced in a press briefing on 4 October. All of the cases occurred in people who worked with sick cows or birds, except for one case announced in September by Missouri public health officials. The person tested positive for H5N1 during routine flu testing after being hospitalised for other underlying health conditions. They didn鈥檛 report any exposure to animals or raw milk 鈥� which can contain the live virus 鈥� raising questions about how they contracted it.
In addition, seven people who interacted with the infected person developed flu-like symptoms, but only one was tested for influenza and the result was negative. Public health officials obtained blood samples from the other six people to test for H5N1 antibodies 鈥� which will determine whether they were infected 鈥� but the results won鈥檛 be available until mid to late October, said at the CDC during the briefing.
That is because they must test samples against the H5N1 virus that infected the person in Missouri. It took the CDC roughly six weeks to reconstruct the virus due to low amounts of genetic material in the person鈥檚 sample, said Daskalakis.
As part of the CDC鈥檚 effort to significantly increase H5N1 surveillance, it extended its seasonal influenza monitoring protocol and advised healthcare workers to conduct influenza testing on anyone who is hospitalised. The agency also recommended further analysis on influenza samples to catch potential H5N1 cases, which is how the case in Missouri was identified.
With the country now entering flu season, the CDC is also asking laboratories to sequence enough influenza samples to detect any novel virus circulating at a 0.14 per cent prevalence, or 1 out of every 700 samples. To identify any unusual flu activity, the CDC says it is monitoring between influenza samples per week, data on respiratory symptoms from roughly 2.5 million people weekly and all emergency department visits with an influenza diagnosis.
It is also granting contracts to laboratories so they can increase testing capacity to tests per week in case of an emergency, with some being able to scale to more than 100,000 weekly tests if needed.
鈥淥ne of the biggest problems we had in the covid-19 pandemic is the lack of testing that was available in the first several months,鈥� says at Johns Hopkins University. 鈥淲e were flying blind with regards to how many cases there were and how the disease was spreading in the US.鈥� Boosting testing capacity should prevent a similar outcome if H5N1 becomes more widespread, he says.
In May, the agency unveiled a new that tracks H5, the influenza subtype that includes H5N1. So far, the system includes more than 300 sites across the US.
Wastewater surveillance is helpful for identifying areas where H5 may be circulating that other surveillance methods miss, says at Johns Hopkins University. 鈥淎lthough, it is a little bit like a needle in a haystack,鈥� she says. 鈥淚f you have small numbers of cases, you may not see the signal as quickly.鈥�
As such, the US government should conduct more active surveillance, such as routinely testing farm workers exposed to sick animals, says Davis. However, the CDC doesn鈥檛 have the authority to do so without farmers鈥� permission. To circumvent this, the agency is recruiting who work with sick cattle to undergo antibody testing, which will give them a better idea of how many people have contracted H5N1 since the outbreak in cattle.
While the current risk of H5N1 remains low for most people, Toner worries that could change if agencies don鈥檛 boost testing even further. 鈥淢y hair is not on fire, but I am concerned,鈥� he says.
