Category: Research

Statistics of SIDS incidences

SIDS in time

Overall statistics of SIDS incidences show that number of sudden deaths of infants declines. However, the biggest decrease we have seen in 90s – the result of the “Back to sleep” campaign. Since then, the decrease is much smaller, almost insignificant.

Sudden Infant Death Syndrome (SIDS) rates declined considerably from 130.3 deaths per 100,000 live births in 1990 to 55.7 deaths per 100,000 live births in 2001. Unknown Cause infant mortality rates have remained unchanged from 1990 to 2010. In 2011, the Unknown Cause mortality rate in infants was 22 deaths per 100,000 live births. Accidental Suffocation and Strangulation in Bed (ASSB) mortality rates remained unchanged until the late 1990s. Rates started to increase beginning in 1998 and reached the highest rate at 17.8 deaths per 100,000 live births in 2008. The total combined Sudden Unexpected Infant Death rate (which includes SIDS, Unknown Cause, and ASSB) declined considerably following the American Academy of Pediatrics safe sleep recommendations released in 1992 the initiation of the Back to Sleep campaign in 1994, and the release of the Sudden Unexplained Infant Death Investigation Reporting Form in 1996. However, the total combined Sudden Unexpected Infant Death rate has not decreased significantly since 1999.

Sudden Infant Death Syndrome (SIDS) rates declined considerably from 130.3 deaths per 100,000 live births in 1990 to 55.7 deaths per 100,000 live births in 2001.
Unknown Cause infant mortality rates have remained unchanged from 1990 to 2010. In 2011, the Unknown Cause mortality rate in infants was 22 deaths per 100,000 live births.
Accidental Suffocation and Strangulation in Bed (ASSB) mortality rates remained unchanged until the late 1990s. Rates started to increase beginning in 1998 and reached the highest rate at 17.8 deaths per 100,000 live births in 2008.The total combined Sudden Unexpected Infant Death rate (which includes SIDS, Unknown Cause, and ASSB) declined considerably following the American Academy of Pediatrics safe sleep recommendations released in 1992 the initiation of the Back to Sleep campaign in 1994, and the release of the Sudden Unexplained Infant Death Investigation Reporting Form in 1996. However, the total combined Sudden Unexpected Infant Death rate has not decreased significantly since 1999.

SIDS per infant group

Sudden infant death syndrome happens from one every 200 births to one every 20000 births. There are several factors that increase the SIDS risk in certain groups of infants:

  1. Gestation age (data for US, in late 90s)
    • at 37–39 weeks of gestation SIDS rate was 0.73/1000
    • at 28–31 weeks of gestation SIDS rate was 2.39/1000
  2. Birth weight (related to gestation age, data for US, late 90s):
    • for infants weighing 1000–1499 g SIDS rate was 2.89/1000
    • for infants weighing 3500–3999 g SIDS rate was only 0.51/1000.
  3. Race/culture (see our explanation of genetics of SIDS, data for US, 2010-2013):
    • for American Indian infants SIDS rate was 0.9/1000
    • for Non-Hispanic Black infants SIDS rate was 0.8/1000
    • for Non-Hispanic White infants SIDS rate was 0.4/1000
    • for Hispanic infants SIDS rate was 0.3/1000
    • for Asian/Pacific Islander infants SIDS rate was 0.2/1000

Comparing SIDS rates to infant mortality rates

Sudden infant death syndrome is not the only reason of infants’ deaths in the world. It is assumed that across the world, the leading causes of premature infant deaths were birth asphyxia, pneumonia, pre-term birth complications, neonatal infection, diarrhoea, malaria, measles and malnutrition. However, when only first world countries are taken into account, some research suggests SIDS is the third the most leading cause of infant mortality. Let’s compare the two rates in United Kingdom and United States:

  1. In UK overall SIDS rate is 0.2/1000, but it’s five times higher when mother is younger than 20. Infant mortality rate there is 4.19/1000, so SIDS is the cause of 5% of premature deaths of infants.
  2. In US overall SIDS rate (averaged across all groups) is 0.5/1000. Infant mortality rate is 5.97, so SIDS is the cause of 8% of premature deaths of infants.

The numbers are pretty similar and in both countries SIDS accounts for less than 10% of all premature deaths.

 

Risk factors of Sudden Infant Death Syndrome

While mechanism of SIDS is not known yet, there are several risk factors that increase the chance of sudden death incidence. These are not causes, but only correlate with this syndrome.

Infants risk factors:

  1. Sleeping position is the most important risk factor for SIDS. Remember to put your child to sleep on the back – it lowers the chance of developing SIDS by half.
  2. Boys are more likely to die because of SIDS, but a large margin. Sex ratio for SIDS is around 1:2, girls vs boys.
  3. Age is an important factor, as the most of SIDS incidences happen between second and fourth months of life. Newborns and children over 1 year old don’t die because of SIDS.
  4. For unknown reasons black, American Indian and Eskimo infants die more often from SIDS than other races.
  5. Passive smoking is also an important risk factor. Remember that smoking next to your infant has long term negative effects (such as high chance of infertility), but also immediately increases SIDS chances.
  6. Low birth weight and premature birth increase the risk of SIDS, for unknown reasons. Some researchers claim it’s due to developing hypophosphatemia, as low birth weight infants have much higher phosphate needs than normal weight infants.

Other risk factors:

  1. If mother is younger than 20, her child has a higher risk of SIDS.
  2. Mother smoking cigarettes during pregnancy also increases chances that a newborn will develop SIDS.
  3. Similarly, infants have a higher chance of dying because of SIDS if mother is using drugs and alcohol during pregnancy. Also, these substances increase substantially the risk of developmental defficiences (usage of antidepressants in pregnancy is linked to autism), so avoid them at all cost.
  4. Lack of adequate prenatal care is also an importan risk factor for SIDS.

 

How is vaccination related to sudden infant death?

Fear of vaccination is quite wide spread. Vaccines are linked (albeit research does not support this link) to autism, but they were some time ago also linked to SIDS incidences. Are vaccines safe to your child? It turns out that yes, they are, and careful research ruled out immunization as a possible cause of sudden infant death syndrome. Even more, vaccines were thought to lower the risk of SIDS:

Immunisations are associated with a halving of the risk of SIDS. There are biological reasons why this association may be causal, but other factors, such as the healthy vaccinee effect, may be important. Immunisations should be part of the SIDS prevention campaigns. [Vennemann et alo, 2007]

This is related to currently prevailing hypothesis about SIDS causes. Paul Goldwater published w 2011 a review on SIDS (Goldwater, 2011) in which he assessed all the hypotheses of SIDS mechanism according to three questions:

  1. Does the hypothesis take into account the key pathological findings in SIDS?
  2. Is the hypothesis congruent with the key epidemiological risk factors?
  3. Does it link 1 and 2?

Some hypotheses did not meet any the criteria and only one (infection) met all three. That might explain apparent lower ratio of SIDS incidences in vaccinated children – stronger immune system might extert protective effect on an infant. This link is putatively confirmed in the 2015 study by German researchers who studied specifically  diphtheria-tetanus-pertussis immunization and its putative role in SIDS:

Increased DTP immunisation coverage is associated with decreased SIDS mortality. Current recommendations on timely DTP immunisation should be emphasised to prevent not only specific infectious diseases but also potentially SIDS. [Müller-Nordhorn et al, 2015]

Other studies claim that this is not the case, as no correlation between vaccination and sudden infant death was observed after correcting for confounding variables:

There is no increased or reduced risk of sudden infant death during the period after the vaccination. The previously reported protective effect seen in case contol studies is based on the inclusion of unvaccinated cases.  [Kuhnert et al, 2012]

Whatever hypothesis about protective (or lack of protective) effect is true, it is absolutely clear that vaccines do not cause SIDS. Having your child immunized will protect it from other diseases, but will not have a negative effect when sudden death is concerned.

Is SIDS linked to genes?

Is SIDS a genetic disease?

Some researchers claim that there are certain mutations in human genome that are responsible for elevated risk of sudden infant death syndrome. For example, in Japan almost 10% of SIDS cases are associated with certain mutations of cardiac ion channels (Otagiri et al, 2009):

Sudden infant death syndrome (SIDS) is multifactorial and may result from the interaction of a number of environmental, genetic, and developmental factors. We studied three major genes causing long QT syndrome in 42 Japanese SIDS victims and found five mutations, KCNQ1-K598R, KCNH2-T895M, SCN5A-F532C, SCN5A-G1084S, and SCN5A-F1705S, in four cases; one case had both KCNH2-T895M and SCN5A-G1084S. (…) Our data suggests that nearly 10% of SIDS victims in Japan have mutations of the cardiac ion channel genes similar to in other countries.

However latest exome sequencing indicates that mutations in ion channels that were supposed to correlate with myocardiopathy-related SIDS incidences (Brion et al, 2009) are much more common than they were thought (Andreasen et al, 2013). In other words, observed genetic associations seem to be only a result of small size sampled.

Also, prevalence of SIDS should be higher in twins if one of children had SIDS incidence. However, recent work by Platt and Pharoah found no evidence that:

In spite of a lower risk of SIDS in twins compared with singletons for each birth weight group <3000 g, one component of the higher crude relative risk of SIDS in twins is attributable to the higher proportion of twins that are of low birth weight. A second component is the higher risk in twins compared with singletons for those of birth weight ≥3000 g. Like sex are at no greater risk than unlike sex twins, which suggests that zygosity is not a significant factor in SIDS.

So, genetics does not seem to be a factor in SIDS. Current analyses do not confirm a link between mutations in human genome and higher risk of sudden infant death syndrome.

SIDS and race

On the other hand, there is a clear correlation between race and frequency of sudden infant death incidences. The frequency (per 100,000 live births) of infant deaths range from 20.3 for Asian/Pacific Islander to 119.2 for American Indians/Alaska Native. African American infants have a 24% greater risk of having a SIDS related death than Caucasian infants. However, this could be explained by cultural factors as more than 50% of African American infants were placed on their tummy for sleeping – the position that is absolutely not recommended and has been linked to SIDS.