My suspicion was confirmed by the Wall Street Journal.
To cite a 99.9% fatality rate, manufacturers don’t have to kill 99.9% of all known bugs. Regulations don’t require them to disclose which bugs they exterminate, just that the products are effective against a representative sample of microbes. For instance, many products can’t kill Clostridium difficile, a gastrointestinal scourge, or the hepatitis A virus, which inflames the liver. Yet by killing other, more common bugs, they can claim 99.9% effectiveness.
This is like arguing with your professor to ask her adjust the exam results’ Bell Curve so your “F” can sneak in as a “D”. As Disraeli said, “Lies, damned lies, and statistics”.