Advancing the Bacterial Hypothesis of Sudden Infant Death Syndrome (SIDS) and Sudden Unexplained Death in Childhood (SUDC): Evidence that Prone Sleeping Position Elevates Bacterial Titres in the Anterior Nares

Abstract Background Sudden Infant Death Syndrome (SIDS) and Sudden Unexplained Death in Childhood (SUDC) are associated with prone positioning, yet the biological mechanism remains unclear. We assessed whether prone position increased bacterial titres in the anterior nares and whether this effect is amplified in the presence of upper respiratory tract infection (URTI). Method This prospective cross-over study required adults, as substitutes for infants, to self-collect nasal swabs at two timepoints, when experiencing an URTI and when healthy. Swab eluates were cultured aerobically and anaerobically on blood agar for total bacterial counts. DNA and RNA were extracted for detection of respiratory viruses. A multivariate analysis accounted for gender, position sequence, breathing mechanism and smoking. The study consisted of 100 adult (>18 years) participants. The final cohort consisted of the 28 participants who contracted an URTI during the study; of these 5 did not provide asymptomatic samples. Results When asymptomatic, prone positioning resulted in increased bacterial titres relative to supine under anaerobic (p=0.0101) and aerobic (p=0.0101) culture conditions. When participants were symptomatic this effect tended to be exacerbated with significantly higher titres observed in prone position under anaerobic (p=0.0001) and aerobic (p=0.0003) conditions. The relationships between position and bacterial titres remained significant after adjusting for potential confounders (p<0.0001). Conclusion We found a significant association between prone positioning and increased bacterial titres in the anterior nares, particularly in the presence of a suspected viral illness. These data strengthen the results of previous studies and provide further support for the bacterial hypothesis of SIDS.