Despite being a dangerous disease for birds, avian flu infections in humans are extremely rare. So much so that the two cases registered in Spain in the autumn of last year have turned out to be the result of environmental contamination and not of real infections. The case is a wake-up call to a disease that is increasingly worrying.
Asymptomatic cases. The two cases now reviewed were detected at a poultry farm in the province of Guadalajara in the fall of 2022. They were two operators who had been working at the facilities of a farm that had suffered an outbreak of the virus for days.
None of the workers showed symptoms but both obtained positive results in their PCRs. In a few days the second tests to which they were submitted were negative, as were other tests to which they were subjected.
Now, five months after the diagnosis, investigations have revealed that the positives could not be due to a real infection, but to a case of environmental contamination. The results of these investigations (which have confirmed what the health authorities were already advancing) have recently been published in an article in Eurosurveillance.
How is it possible? It should be remembered from time to time that any medical test always implies a margin of error, greater or lesser. Tests can fail for a huge number of reasons such as manufacturing defects, human error in testing, or simply because human biology is capricious and there is some natural variability in our bodies that can affect test results. doctor.
Sometimes Tests fail because there is a small discrepancy between what they measure and the disease itself. This is one of those cases, and this small discrepancy was caused by environmental circumstances.
The PCR tests, explains Ursula Hölfe, from the University of Castilla-La Mancha, who did not take part in the study, detect the presence of genetic material (in this case the H5N1 virus) on the surface (the analyzed mucosa. This genetic material it can get there simply by being present in the environment, which is to be expected in a poultry farm that has suffered an outbreak of the virus.
No infection. The presence of genetic information from the virus, or from the virus itself, in a person’s mucosa does not necessarily imply infection (which is what we really want to find out). Viruses can get into our bodies and fail to reproduce successfully, and this would in fact be typical of bird flu, a flu that rarely infects humans.
The absence of other positive diagnostic tests together with the fact that they were asymptomatic cases had already made some experts and health authorities suspicious. Despite this, confirmation of this suspicion has not been possible until now.
Change the protocols. These false positives could have been avoided, some experts say. In statements to the Science Media Centre, Elisa Pérez, from the National Institute for Agricultural and Food Research and Technology (INIA-CSIC) advocates changes in the protocols, for example carrying out the tests in medical centers instead of in situ.
“It seems very appropriate to change the protocol (…): that the samples are taken in a medical center and not the farm facilities and that a few days have passed since the last contact with the contaminated area. All this, of course, if we are talking about totally asymptomatic people, as happened in this case.”
A growing problem. Bird flu is a problem that seems to be on the rise. Partly due to the nature of the disease and partly due to the change in the agricultural exploitation model, the disease worries experts not only for its economic impact, but also for its potential to affect humans.
This double negative is good news because of what it tells us about the ability of the virus to affect us, but also because it shows that the surveillance protocols for the disease have worked. Despite this, it is also a wake-up call for a simple reason: they could have worked better.
And it is that the fact that this virus does not currently have the capacity to cause major problems in humans does not imply that we should relax. A few months ago, an outbreak at a mink farm in Galicia worried some. It is not for less, if the mutations allow the virus to affect other mammals, it is not possible to rule out its jump to humans.
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