What is a critical symptom of tracheoesophageal fistula (TEF) in infants?

In infants with tracheoesophageal fistula (TEF), a critical symptom is the aspiration of milk or other feeding substances into the lungs. This occurs due to an abnormal connection between the trachea and esophagus; when the infant swallows, instead of directing the milk down the esophagus, it can inadvertently enter the trachea. This can lead to serious respiratory complications such as choking, coughing, gagging, and even pneumonia. The presence of milk in the lungs can severely compromise the infant's ability to breathe and can lead to further medical complications if not addressed promptly.

Other symptoms associated with TEF may include difficulty feeding or respiratory distress, but the aspiration of milk directly into the lungs is particularly critical and directly indicative of the condition.