Whenever doctors say that an infectious agent is not spread through the air, they mean that our airways ordinarily have adequate defenses or that the agent is not found anywhere in the airwaves (not in saliva, nasal secretions, not in coughs or sneezes, etc.).
If an infectious agent is in the airwaves, as it more than likely is, can these airway defenses be breached?
Of course they can.
Here are scenarios:
1. the epithelium of the nasal or oral airways is damaged (root canal, tooth abscess, bleeding gums, mouth or nasal ulcers), exposing the infectious agent to the bloodstream.
2. Mucus secretion is impaired, allowing the agent to enter the lungs and the digestive tract, either of which could be compromised.
3. Realizing that about half of the mucus we produce ends up in the stomach, even if the agent is effectively trapped in mucus, the digestive system defenses may be compromised. This involves either ulcerations in the lining of the esophagus, stomach, or intestines, or poor stomach acid production coupled with poor bile secretion. A particularly troublesome combination is a person taking acid blockers and eating low-fat meals. A person without a gall bladder or with a leaky gut is at increased risk.