How can mucus from an upper respiratory infection (URI) enter the stomach?

How Mucus from Upper Respiratory Infections Enters the Stomach

Mucus from an upper respiratory infection primarily enters the stomach through the process of aspiration and swallowing, with thicker viscous secretions more likely to flow down the throat during sleep or when lying down.

Pathways of Mucus Movement from URI to Stomach

Primary Mechanism: Aspiration and Swallowing

1. Postnasal Drip Mechanism

   • During a URI, excess mucus production in the nasal passages and sinuses leads to postnasal drip 1
   • This mucus naturally flows down the posterior pharyngeal wall behind the palatopharyngeal arch (visible as a "reddish curtain sign" in 90% of patients with postnasal drip) 2
   • The mucus then enters the oropharynx where it is typically swallowed consciously or unconsciously

2. Mucociliary Clearance

   • Mucus that enters the trachea is gradually moved upward by the mucociliary transport system of the respiratory tract 1
   • Once transported to the upper airway, this mucus is eventually swallowed and enters the digestive system

Factors Affecting Mucus Movement

1. Viscosity of Secretions

   • Thicker, more viscous mucus (similar to glycerin solutions in experimental models) is more likely to flow into the respiratory organs, especially during sleep 1
   • This viscous mucus can then be transported back up and swallowed

2. Body Position

   • Lying down or sleeping position significantly increases the likelihood of mucus flowing from the nasal passages into the throat 1
   • In radioisotope-tracer studies, 45% of healthy adults were found to aspirate during sleep 3

3. Impaired Swallowing

   • Persons with abnormal swallowing (due to depressed consciousness, respiratory tract instrumentation, or gastrointestinal diseases) are particularly likely to aspirate mucus 3

Clinical Implications

1. Risk of Lower Respiratory Tract Infection

   • While most mucus is swallowed and enters the stomach, some may enter the lower respiratory tract through aspiration 3
   • This is the primary route for bacterial entry into the trachea and can lead to respiratory infections 3

2. Management Considerations

   • Adequate hydration is recommended to help thin mucus secretions 4
   • Saline nasal irrigation provides modest symptom improvement and helps clear mucus 4
   • Elevating the head while sleeping may reduce postnasal drip entering the respiratory tract 4

Important Caveats

• The stomach's acidic environment (pH < 2) typically destroys most bacteria in swallowed mucus, providing protection against infection 3
• However, when gastric pH increases to ≥ 4 (due to medications, age, or other factors), microorganisms can multiply in the stomach 3
• Patients should seek medical attention if fever > 38°C persists for more than 48 hours or if breathing difficulty occurs 4

Remember that while most mucus from URIs is swallowed and enters the digestive tract, the portion that may enter the respiratory tract is a potential concern for developing lower respiratory infections, especially in vulnerable populations.