Written by Scott Myers, MD
Several studies have shown that, although many individuals with autism live long and healthy lives, there is an increased risk of death (mortality) associated with autism1-5. A standardized mortality ratio (SMR) is the ratio of the observed number of deaths to the expected number of deaths, so any value greater than 1.0 means that the observed death rate exceeds expectations.
Studies in the USA (California), Denmark, and Sweden have found SMRs associated with autism to range from 1.9 to 5.61-5. This means that individuals with autism have a somewhat higher risk of death than other individuals do. However, to put this number in perspective, it is important to note that the mortality rate in the general population is quite low. For example, in 2008, the mortality rate for all children under 5 years old was 8 per 1,000. The SMRs for autism indicate that the risk for children with autism is roughly between 16 and 60 per 1000—still very low but enough of a risk that families and providers should take extra precautions to ensure safety. The elevated death rate associated with autism is largely accounted for by the subset of individuals who also have moderate, severe, or profound intellectual disability (mental retardation) and epilepsy.
The risk of accidental death by drowning was elevated in people with autism in California, where 5% (11/202) of all of the deaths of individuals with autism between 1983 and 1997 were caused by drowning. This is substantially higher than the combined rate of 0.4% when the Swedish and Danish studies are combined, perhaps due to increased access to pools and other bodies of water in California.
Although death rates for almost all causes were higher for individuals with moderate, severe, or profound intellectual disability, drowning and other accidental deaths were found to occur at a higher rate than expected even in those without epilepsy or severe intellectual disability. In the California study, the SMR for drowning in individuals with autism who had mild or no intellectual disability was 3.9, and the SMR for those with autism and moderate, severe, or profound intellectual disability was 13.71.
Information about mortality that includes specific causes of death is important because it may influence treatment strategies, including prevention. These statistics remind us that children and adults with autism are at risk for accidental death, especially by drowning, and that strategies to increase water safety in people with autism may save lives.
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Citation for this article:
Myers, S. (2011). Review of mortality in autism drowning. Science in Autism Treatment, 8(1), 8.