SIDS or not SIDS, that is the question
As the basis for the critical development period was the observation of the peak of SIDS cases in the 3rd month of life, we sought out to understand this property, especially in the light of newer publications questioning the existence of SIDS as a separate condition. The simple correlation analysis identified 12 cause groups that had at least a 0.5 correlation (Pearson standard correlation coefficient test) with SIDS (Fig 1), from all 77 disease groups that were available after our harmonization procedure described in the Methods section. The list of 12 disease groups that have similar death patterns is: Ill-defined and unknown cause of mortality, Cardiac arrest - cause unspecified, Acute vascular disorders of intestine, Chronic respiratory disease originating in the perinatal period, Acute bronchiolitis, Viral pneumonia, Hepatic failure, Sepsis - unspecified organism, Group of intestinal disorders, Anoxic brain damage - not elsewhere classified, Sepsis due to Gram-negative organisms and of course SIDS.
Another statistical feature of SIDS is the drop of mortality due to the “Back to Sleep” campaign. Here we test for a common argument of misdiagnosis. However, since a drop in mortality over time is expected because of the advances in medicine and childcare, we suspected that most of the diseases would meet the criteria. From 76 disease groups that we analyzed, 33 met the criteria of correlated drop in mortality (positive correlation with SIDS / p-value < 0.005 / Pearson standard correlation coefficient test). We compared these diseases with the 13 disease groups which we have already found to peak in 3rd month and we ended up with 4 groups which are candidates for further investigation (Fig.2): Cardiac arrest - cause unspecified, Chronic respiratory disease originating in the perinatal period, Viral pneumonia, Anoxic brain damage- not elsewhere classified.
Gestation age negatively correlates with age of death for SIDS
We compared gestation age with age of death for all disease groups. We found only four causes of death where preterms die later than full term newborns (with the following conditions: linear regression with slope less than 0 and p-value less than 0.05): SIDS, Necrotizing enterocolitis in newborn, fetal and newborn aspiration, and acute bronchiolitis. Out of those additional three, acute bronchiolitis is the only disease that has a peak of deaths during the third month, as noted in the previous section. The other two diseases usually occur before the newborn is discharged from the hospital and goes home. The relationship between gestational age and age of death for all four diseases is shown in Fig.3.
To verify that preterms die later than full term newborn in case of SIDS we repeated the analysis by splitting the data into groups: before, during and after the “Back to Sleep '' campaign. This was to remove the possibility that change in diagnostics was influencing the result. As seen in Fig. 4, the relationship remains significant in all three groups separately.
Additionally, to remove the effect of transitioning between two ICD versions (and merging, replacing or removing some conditions), we repeated the analysis for ICD-9 and ICD-10 separately. In addition to SIDS, which consistently comes up in all subsets as statistically significant, we found Necrotizing enterocolitis in newborn, Fetal and newborn aspiration, and Poisoning in ICD-9, and Other bacterial sepsis of newborn, Necrotizing enterocolitis in newborn, Car accident, Suffocation and Assault by unspecified means in ICD-10.