I think it has more to do with an interruption of the natural immune system building. The infant immune system builds from the bacteria it encounters in living. They are constantly stuffing things in their mouth, and this helps reinforce their immune system.
By interrupting this process with "sterile" lifestyles, it weakens the overall immune system and makes people more likely to purchase OTC and prescription medications from doctors. Many foreign nations do not have nearly the obsession with sterile living in the home, and those people do not suffer common colds nearly as often (among other things). This isn't to say that medical science or vaccines are completely invalid, but the western obsession with them ultimately does more harm than good.
Think Quarians from Mass Effect - a species of people who lived on sterile spacecraft for so long that their bodies lost their natural immune system and are almost completely reliant on chemical intervention for infection treatment/control.
There could be "deliberate poisoning" in all of that, too - but I think this is largely a crayon for people to munch on. They don't want defective servants, they want a controllable population of them. They also want to be able to play eugenics with their branch blood lines and to breed from them in the future. They don't want to poison the population.