An apple a day keeps the doctor away;An onion a day keeps everyone away.More seriously, how could an onion attract bacteria or viruses?If it did then the fact that onions are mildly bactericidal would stop the contaminated onion being much of a problem anyway.Also my mum likes onions, but my dad doesn't, so most of the time there is some, but not much onion in the food.That means there is often p