This is what is currently circulating on the internet:
In 1919 when the flu killed 40 million people, there was a Doctor who
visited many farmers to see if he could help them combat the flu. Many of
the farmers and their family had contracted it, and many died.
The doctor came upon one farmer, and to his surprise, everyone in the
household was very healthy. When the doctor asked what the farmer was
doing that was different, the wife replied that she had placed an unpeeled
onion in a dish in the rooms of the home (probably only two rooms back
then). The doctor couldn't believe it and asked if he could have one of
the onions and place it under the microscope. She gave him one, and when
he did this, he did find the flu virus in the onion. It obviously
absorbed the bacteria, therefore, keeping the family healthy.
visited many farmers to see if he could help them combat the flu. Many of
the farmers and their family had contracted it, and many died.
The doctor came upon one farmer, and to his surprise, everyone in the
household was very healthy. When the doctor asked what the farmer was
doing that was different, the wife replied that she had placed an unpeeled
onion in a dish in the rooms of the home (probably only two rooms back
then). The doctor couldn't believe it and asked if he could have one of
the onions and place it under the microscope. She gave him one, and when
he did this, he did find the flu virus in the onion. It obviously
absorbed the bacteria, therefore, keeping the family healthy.
TAKING IT APART
First let's take apart the story. According to this story, a doctor took an onion that had been sitting in a dish and looked at it under the microscope. He apparently found the flu virus in the onion. What I do know is that in 1919, the only type of microscope available would be an ordinary light microscope. These types of microscopes do not have a resolution anywhere near enough to see a virus! To see a virus, you would need an electron microscope and the earliest version of these wasn't invented until the 1930's. So no, the doctor did not see the virus in the onion.
Second, this story refers to the flu virus as a bacteria. In reality, bacteria and viruses are very different organisms. A virus must find a host and invade its cells in order to reproduce. Bacteria, on the other hand, merely need some type of 'food' in order to replicate...and many natural food source we have will suffice for any number of different strains of bacteria.
Third, I cannot find ANY scientific papers that provide evidence of onions attracting/absorbing the flu virus or helping heal people who have the flu.
So, with these three lines of reasoning, I have to say the story is a hoax.
HOWEVER...there is a evidence that onions can fight off some bacteria (but not a virus).
There are three lines of evidence regarding onion's influence on bacteria.
First, placing cut onions around the house is a very old remedy that goes back at least 1000 years and throughout history to the present day. Usually when something lasts this long, there is some kernel of truth in it somewhere that warrants scientific investigation.
Second, there are scientific papers that show the juice of an onion contains thiosulphinate, which has been proven to kill some common types of bacteria.
Third, rubbing a cut onion (and thus exposing the juice) on cuts and wounds has been shown to reduce infection and speed up healing.
So, the bottom line is that onions do have an effect on some bacteria. But the way the story is currently being told is false.
Here is an INTERESTING TWIST that I think merits attention. Many people who become seriously ill with the flu, end up with a compromised immune system that leaves them open to 'opportunistic' bacterial infections. Their body's defense system is just not up to the task of warding off bacteria that they normally would be able to defend against. Indeed, many people who die after having been seriously ill with the flu actually die from one of these other infections, such as pneumonia. It might be possible that leaving a cut onion near a person when they are seriously ill will help keep these bacteria away (there is a reason you can smell an onion from a distance).
If nothing else, the person who cut up the onions will have probably spilled some of the juice on their hands and therefore cleaned their own hands of bacteria before they touched the patient.
However, washing their hands with soap and water for at least 20-30 seconds before and after tending to the sick patient and wearing a mask would do a better job of this.