Global prevalence of autism: A systematic review update, (2022), Zeidan J., Fombonne E., Scorah J., Ibrahim A., Durkin M., Saxena S., Yusuf A., Shih A., Elsabbagh M.

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Prevalence estimates of autism are essential for informing public policy, raising awareness, and developing research priorities. Using a systematic review, we synthesized estimates of the prevalence of autism worldwide. We examined factors accounting for variability in estimates and critically reviewed evidence relevant for hypotheses about biological or social determinants (viz., biological sex, sociodemographic status, ethnicity/race, and nativity) potentially modifying prevalence estimates of autism. We performed the search in November 2021 within Medline for studies estimating autism prevalence, published since our last systematic review in 2012. Data were extracted by two independent researchers. Since 2012, 99 estimates from 71 studies were published indicating a global autism prevalence that ranges within and across regions, with a median prevalence of 100/10,000 (range: 1.09/10,000 to 436.0/10,000). The median male-to-female ratio was 4.2. The median percentage of autism cases with co-occurring intellectual disability was 33.0%. Estimates varied, likely reflecting complex and dynamic interactions between patterns of community awareness, service capacity, help seeking, and sociodemographic factors. A limitation of this review is that synthesizing methodological features precludes a quality appraisal of studies. Our findings reveal an increase in measured autism prevalence globally, reflecting the combined effects of multiple factors including the increase in community awareness and public health response globally, progress in case identification and definition, and an increase in community capacity. Hypotheses linking factors that increase the likelihood of developing autism with variations in prevalence will require research with large, representative samples and comparable autism diagnostic criteria and case-finding methods in diverse world regions over time.

Lay Summary

We reviewed studies of the prevalence of autism worldwide, considering the impact of geographic, ethnic, and socioeconomic factors on prevalence estimates. Approximately 1/100 children are diagnosed with autism spectrum disorder around the world. Prevalence estimates increased over time and varied greatly within and across sociodemographic groups. These findings reflect changes in the definition of autism and differences in the methodology and contexts of prevalence studies.

Citation: Zeidan J, Fombonne E, Scorah J, Ibrahim A, Durkin MS, Saxena S, Yusuf A, Shih A, Elsabbagh M. Global prevalence of autism: A systematic review update. Autism Res. 2022 May;15(5):778-790. doi: 10.1002/aur.2696. Epub 2022 Mar 3. PMID: 35238171; PMCID: PMC9310578.

Autism Spectrum Disorders in Greece: Nationwide Prevalence in 10–11-Year-Old, (2020), Thomaides L., Mavroeidi N.

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Autism spectrum disorders (ASD) constitute a public health concern with increasing prevalence worldwide. We aimed to estimate prevalence and age at diagnosis in Greece, where no large-scale prevalence study has ever been conducted. Aggregate data were collected on ASD diagnoses by gender and calendar year of diagnosis up to 2019, for children born in 2008 and 2009, from the Centers for Educational and Counseling Support, which evaluate children to receive special educational support in school. Coverage was 87.1% of centers and 88.1% of schoolchildren born in 2008–9. ASD prevalence overall was 1.15% (1.83% males, 0.44% females; ratio 4.14:1), ranging from 0.59% to 1.50% in Greece’s 13 regions. In five regions, prevalence differed significantly between centers. Overall, only 3.8% of diagnoses were made before the fourth year after birth and 42.7% before the sixth year, with considerable variation between regions. Approximate mean age at diagnosis was six years and one month, and about three months earlier for girls than for boys. Our results provide evidence-based information to guide service planning and development at national and regional levels. Particular attention should be paid to smoothing out inequalities regarding service accessibility and provision. Emphasis should be given to earlier identification and diagnosis of ASD.

Citation: Thomaidis L, Mavroeidi N, Richardson C, Choleva A, Damianos G, Bolias K, Tsolia M. Autism Spectrum Disorders in Greece: Nationwide Prevalence in 10-11 Year-Old Children and Regional Disparities. J Clin Med. 2020 Jul 8;9(7):2163. doi: 10.3390/jcm9072163. PMID: 32650567; PMCID: PMC7408756.

The epidemiology of autism spectrum disorder and factors contributing to the increase in its prevalence, (2022), Depastas, C. Kalaitzaki, A.

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Autism spectrum disorder (ASD) is a multifactorial neurodevelopmental disorder which has attracted the interest of researchers in many scientific fields. The prevalence of a disease or a disorder is important for healthcare and socio-economic reasons. According to the World Health Organization (WHO), currently, 1 in 160 children is born with ASD (0.63%), possibly a conservative estimate, as many studies have reported a prevalence higher than 1%. Even so, the WHO rate is approximately 14 times higher than that reported in the first epidemiological study on ASD, which was conducted in the UK 50 years ago. It is currently estimated that approximately 60 million people worldwide have ASD. Diagnosis and documentation of these individuals is challenging, due to the nature of the disorder and its broad spectrum. Many countries have no epidemiological data on ASD and several epidemiological studies on ASD record significant methodological limitations, but the currently available data indicate that the prevalence of ASD has risen over the years. The interpretation of this trend remains uncertain, but several factors have been documented that may have contributed to this apparent increase, including revision of the diagnostic criteria, overdiagnosis, scientific advances, accessibility to services, increase in social awareness, and improvement in the methodology applied in the epidemiological studies, in addition to environmental and other factors.

Citation: Depastas, C., Kalaitzaki, A. (2022). The epidemiology of autism spectrum disorder and factors contributing to the increase in its prevalence. A.Archives of Hellenic Medicine / Arheia Ellenikes Iatrikes . May/Jun2022, Vol. 39 Issue 3, p308-312. 5p.

Epidemiological controversies in autism, (2020), Forbonne, E.

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Once considered to be rare with a prevalence of 4–5/10,000, autism today has a prevalence in the range of 0.9–1.5%. The increased prevalence reflects mostly a broadening of the diagnosis, and improved awareness and identification among children. The hypothesis that the rise in autism prevalence was due to increased use of childhood vaccines has been refuted in well-controlled and replicated studies. Few environmental causes are well established (advanced paternal age, prenatal exposure to valproate); most other findings require replication.

Citations: Eric Fombonne, (2020). Epidemiological controversies in autism. Swiss Arch Neurol Psychiatr Psychother. 2020;171:w03084

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