“The U.S. infant mortality rate is higher than those in most other developed countries, and the gap between the U.S. infant mortality rate and the rates for the countries with the lowest infant mortality appears to be widening.” 
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The burden of a high Infant Mortality Rate (IMR) in the United States is a perplexing situation. We spend the most per capita on healthcare; have some of the greatest advancements in technology/science/infrastructure, large physician pools, etc. The question remains, why is the IMR so high in the USA compared to other developed nations?
First, lets take a look at what infant mortality is. The general definition is: death of an infant less than 1 year of age. Now the causes of death vary, from birth complications, congenital malformations, drug use during pregnancy, prematurity, etc. All of these factors contribute to infant death. In addition to these identifiable causes, some causes of infant death remain unknown. This is particularly worrisome and impedes our ability to understand why IMRs are so high in the USA. These unknown causes of death are categorized as Sudden Unexpected Death Syndrome (SUDS) and Sudden Infant Death Syndrome (SIDS).
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Although shrouded in mystery and controversy, SIDS is a valid form of classifying infant death. As a result, SIDS is identifiable and diagnosable, having a consistent clinical/histological/biochemical picture. SIDS is defined as:
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Moreover, other clinical/histological/autopsy findings help define SIDS. “For instance, the predictive value of finding thymic petechiae (gross and/or microscopic examination) would be 95.5% predictive of SIDS.” Additionally, fluid-filled lungs, brain edema, liquid blood, empty bladder, fatty liver, and focal granule cell bilamination to name a few, are seen in SIDS . Patients often present with bleeding/foaming/mucus from the mouth/ears, hypoxic changes (e.g. perioral cyanosis), and no signs of trauma. .
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Of course, with hypoxic changes one would suspect apnea/asphyxiation/suffocation to be the underlying cause of death in SIDS. One of the leading theories is failure of auto-resuscitation during sleep . All rights reserved. See citation below.
As a result of this theory, safe sleep recommendations were made from 1992 onwards and saw great success (on paper). Although SIDS rates significantly declined during this time, other causes (known and unknown) increased. For instance, rates of “suffocation in bed” (ICD-9 E913.0) increased at an average annual rate of 11.2% . Moreover, with a recent change from ICD-9 to ICD-10, classification of deaths gets even more complicated and elusive . Thus, when considering overall rates of SIDS and IMR, the slow down-trend has remained fairly consistent overtime (slow down-trend).
“As mentioned above, mechanisms culminating in asphyxia cannot provide the answer to SIDS because the findings in asphyxial death fly in the face of pathological evidence; especially in regard to the number and distribution of petechiae, not to mention organ weight information.”  A significant point is made in the statement above, that the physical findings (on autopsy) are discordant with asphyxial death. Brain swelling/edema is inconsistent with acute hypoxia (excluding HACE, of course). Moreover, “Liquid (unclotted) blood within the chambers of the heart, and increased cross-linked fibrin degradation products (seen in toxaemia/sepsis)”  lends support to the idea that SIDS has a cause other than asphyxia (infection/autoimmunity). The most alarming pathological finding in SIDS is focal granule cell bilamination (GCB) in the dentate gyrus. “Dentate lesions in a large subset of infants with sudden unexplained death may represent a developmental vulnerability that leads to autonomic/respiratory instability or autonomic seizures, and sleep-related death when the infants are challenged with homeostatic stressors.” . Essentially, these brain lesions (congenital or acquired is uncertain) lead to vulnerabilities in respiratory drive. Troubled with acute stressors, this drive may stop and lead to death. GCB is also seen in temporal lobe epilepsy. 
After much scrutiny, it appears that SIDS is named justly so. It is a syndrome, consisting of genetic, environmental, toxic, and social factors. SIDS is central to the IMR question for this reason; it mirrors the gap between the USA and other countries; our SIDS and IMR burdens remain high. One theme that’s never late to the party, vaccination dangers/pros. Why? Well, the USA has one of the highest numbers of vaccines recommended before age 12 months. Are the abnormally high SIDS/IMRs and the high number of vaccines given during the 1st year of life, correlated? “Linear regression analysis of unweighted mean IMRs showed a high statistically significant correlation between increasing number of vaccine doses and increasing infant mortality, with r = 0.992 (p = 0.0009).”  Essentially, at a certain dose/level, increasing the number of vaccinations increases infant mortality! I believe this to be one part of the problem. Aluminum, thimerosal, and ingredients alike tax the body. With genetic predisposition (GCB), environmental toxins (liquid blood – toxemia/infection), and chemical toxins (vaccine ingredients, foods, etc.) particularly vulnerable infants unfortunately succumb.
 All rights reserved. See citation below. Prevnar 13, Pentacel, Tripedia vaccine monographs (“package insert”)
Now that the problem/cause has been identified, we must figure out what actions can be done to protect, reduce, and help fight SIDS. Obviously, in the USA (and other nations) we face many social/societal issues. From homelessness to poverty and substance abuse, these stressors affect everyone, especially pregnant women. We must ensure women have access to basic human and medical needs to bring healthy infants to term. Moreover, we must recognize that certain things aren’t always as they appear. It’s imperative to do your own research. What am I referencing here is vaccines, of course. In my view, vaccines are great, work great, and are a great thing for humans. However, greedy people and corporations have undermined vaccine research/manufacturing/production. We must demand safe products. Oddly enough, some research shows vaccines protect against SIDS, this seemingly contradictory data must be scrutinized, not because it’s wrong, but because it tells us that we still understand little about immunizations, immunity, and the many intricacies that occur in vivo vs. in vitro. Moreover, the genetic component of SIDS remains to be elucidated. Fatty liver change (and known oxidative stress during vaccination) points to inherited mitochondrial disease/fatty acid beta-oxidation deficiencies.  Moreover, its been postulated that certain deficiencies (magnesium) may play a role in SIDS pathogenesis.  Vitamin C may also play a crucial role. Vaccination has been shown to increase Vitamin C utilization. As such, supplementation has been hypothesized to mitigate adverse reactions to vaccines.  All in all, SIDS may be an unavoidable syndrome, however, certain risk factors are modifiable, meaning we can change them (i.e. like not smoking during pregnancy, or around pregnant women – 2nd hand smoke). Ultimately, we must collectively work to reduce SIDS by decreasing our modifiable risk factors.
 Weber, Martin. Et Al. “Post-mortem investigation of Sudden Unexpected Death in Infancy: Role of autopsy in classification of death.” Forensic Pathology Reviews. DOI 10.1007/978-1-61779-249-6_2 (2011)
[?] https://www.cdc.gov/sids/pdf/suidmanual/chapter9_tag508.pdf – ICD codes
[?] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC108000/ – curlin protein
[?]http://www.microbiologyresearch.org/docserver/fulltext/jmm/51/11/mjm5111.1009.pdf?expires=1477713909&id=id&accname=guest&checksum=7F56C7C9004A66F445DC0CDA07B20357 – curlin protein