Nasal obstruction due to mild infection may well be the trigger for apnea and asphyxia in the sudden death (SUD) syndrome in infancy. This hypothesis is based on the well known reluctance of infants to breathe through their mouths. Choanal atresia is a recognized cause of neonatal death. Some babies appear to be almost completely unable to adopt oral respiration and this sometimes persists up to 5 or 6 months of age. These unexpected deaths almost always occur at night, when the infant is unobserved and asleep. The postmortem evidence of infection can account for a collection of nasal secretion.
The records of 28 infants (among 19,000 live births) who died with the SUD syndrome and who had carefully recorded "well baby visits" were reviewed. The findings failed to indicate any physical or immunological defect, allergy, or injury sufficient to account for this terminal event. All deaths occurred at less than 6 months of age.
Shaw EB. Sudden Unexpected Death in Infancy Syndrome. Am J Dis Child. 1968;116(2):115-119. doi:10.1001/archpedi.1968.02100020117001