Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by differences with social interaction, communication, and restricted or repetitive behaviors.
Studies suggest that autism prevalence rates have been increasing globally in recent decades. However, it’s unclear if this represents a true increase in cases or if it’s due to factors like greater awareness, changes in diagnostic criteria, and improved identification.
As autism rates appear to be rising worldwide, it’s crucial to understand the factors influencing prevalence estimates and ensure access to timely diagnosis, support, and services for autistic individuals and their families.
Salari, N., Rasoulpoor, S., Rasoulpoor, S., Shohaimi, S., Jafarpour, S., Abdoli, N., Khaledi‑Paveh, B., & Mohammadi, M. (2022). The global prevalence of autism spectrum disorder: a comprehensive systematic review and meta-analysis. Italian Journal of Pediatrics, 48(1), 112. https://doi.org/10.1186/s13052-022-01310-w
Key Points
- This systematic review and meta-analysis aimed to determine the global prevalence of autism spectrum disorder (ASD) in high-risk groups by continent. The study included 74 studies with 30,212,757 participants from 2008 to July 2021.
- The global prevalence of ASD was found to be 0.6% (95% CI: 0.4-1%). Subgroup analyses showed the prevalence of ASD was 0.4% in Asia, 1% in America, 0.5% in Europe, 1% in Africa, and 1.7% in Australia.
- Factors like geographical location, diagnostic criteria, screening tools, and study population significantly affected the estimated prevalence of ASD. The prevalence decreased with increasing sample size and year of study.
- While informative, the research had limitations such as differences in diagnostic tools, sample sizes, and limited access to some studies due to language barriers.
Rationale
Autism spectrum disorder is a neurodevelopmental condition usually diagnosed before age 3 (but sometimes later into childhood and adulthood) that impacts communication and interaction abilities.
Although traits vary, ASD affects a significant portion of the global population. Obtaining an accurate estimation of ASD prevalence is crucial for determining the economic burden, health services needs, and appropriate allocation of resources to support autistic individuals and their families (Boswell et al., 2014; Rice et al., 2012).
Previous studies have shown a rising trend in ASD diagnoses in recent decades, with prevalence varying widely between countries (Chiarotti & Venerosi, 2020; Qiu et al., 2020).
This systematic review and meta-analysis aimed to provide an updated and comprehensive estimate of the global prevalence of ASD to inform public health strategies.
Method
This systematic review and meta-analysis followed PRISMA 2020 guidelines. Electronic databases were searched for eligible studies published from 2008 to July 2021.
Inclusion criteria were: 1) cross-sectional or cohort studies, 2) articles in English or Persian, 3) use of valid ASD diagnostic tools, and 4) reported information on ASD prevalence.
Study quality was assessed using the STROBE checklist. Random-effects meta-analysis was used to estimate the global ASD prevalence.
Subgroup analysis by continent and meta-regression for sample size and study year were conducted.
Sample
The meta-analysis included data from 30,212,757 participants across 74 studies. Studies were from Asia (26), Africa (4), Europe (25), the United States (16) and Australia (3). Participant ages ranged from 0 to 27 years old.
Results
The global prevalence of ASD was estimated to be 0.6% (95% CI: 0.4-1%). In subgroup analysis, the prevalence was 0.4% in Asia, 1% in America, 0.5% in Europe, 1% in Africa, and 1.7% in Australia.
Meta-regression showed the prevalence of ASD decreased with increasing sample size (p<0.05) and study year (p<0.05).
Insights
This comprehensive meta-analysis provides an updated estimate of the global prevalence of ASD.
The findings highlight significant variation in ASD prevalence between continents, with the highest rates in Australia and the lowest in Asia.
Reasons for these differences may include access to diagnostic services, cultural perspectives impacting diagnosis, and study methodologies.
Interestingly, ASD prevalence estimates decreased in studies with larger sample sizes and those conducted more recently. This may reflect improved study designs that avoid overestimation.
Future research should aim to elucidate reasons behind the geographical differences in prevalence and trends over time. Standardizing diagnostic criteria and screening methods globally would allow for better comparisons.
Strengths
This study had several strengths, including:
- Comprehensive literature search
- Large pooled sample size of over 30 million participants
- Used a validated quality assessment tool (STROBE checklist)
- Thorough statistical analyses including subgroups and meta-regression
- Findings provide a useful synthesis of current global epidemiological data on ASD
Limitations
Despite strengths, this study also had some limitations:
- Differences in screening and diagnostic tools used across studies, impacting comparability
- Wide variation in sample sizes across included studies
- Review was limited to studies published in English or Persian, potentially underrepresenting research from some regions
- Majority of studies came from Western countries, limiting the generalizability of the global prevalence estimate to lower-income nations
- Some geographical regions had limited representation in the included studies
Implications
This study provides a current estimate of the global prevalence of ASD, highlighting its significant impact as a global health issue.
The findings underscore the need for culturally sensitive screening, diagnosis, and support services to be accessible worldwide.
Understanding the prevalence of autism can guide the appropriate allocation of healthcare, education and social support resources.
Policymakers should be aware of the factors influencing prevalence estimates, such as geographical and cultural variables.
Overall, further research is needed to understand the increasing prevalence of ASD better.
References
Primary reference
Salari, N., Rasoulpoor, S., Rasoulpoor, S., Shohaimi, S., Jafarpour, S., Abdoli, N., Khaledi‑Paveh, B., & Mohammadi, M. (2022). The global prevalence of autism spectrum disorder: a comprehensive systematic review and meta-analysis. Italian Journal of Pediatrics, 48(1), 112. https://doi.org/10.1186/s13052-022-01310-w
Other references
Boswell, K., Zablotsky, B., & Smith, C. (2014). Predictors of autism enrollment in public school systems. Exceptional Children, 81(1), 96-106. https://doi.org/10.1177/0014402914532230
Chiarotti, F., & Venerosi, A. (2020). Epidemiology of autism spectrum disorders: A review of worldwide prevalence estimates since 2014. Brain Sciences, 10(5), 274. https://doi.org/10.3390/brainsci10050274
Qiu, S., Lu, Y., Li, Y., Shi, J., Cui, H., Gu, Y., Li, Y., Zhong, W., Liu, Y., Zhu, X., Liu, Y., & Cheng, Y. (2020). Prevalence of autism spectrum disorder in Asia: A systematic review and meta-analysis. Psychiatry Research, 284, 112679. https://doi.org/10.1016/j.psychres.2019.112679
Rice, C., Rosanoff, M., Dawson, G., Durkin, M. S., Croen, L. A., Singer, A., & Yeargin-Allsopp, M. (2012). Evaluating changes in the prevalence of the autism spectrum disorders (ASDs). Public Health Reviews, 34(2), 17. https://doi.org/10.1007/bf03391685
Keep Learning
Here are some reflective questions related to this study that could prompt further discussion:
- How might cultural perspectives and norms influence the identification and diagnosis of autism in different regions of the world?
- What are some potential reasons for the variation in autism prevalence estimates between continents? Consider access to healthcare, awareness, stigma, etc.
- This study found that prevalence estimates decreased with larger sample sizes and more recent study years. Why might this be the case? What does this suggest about the true prevalence of autism?
- Based on the insights from this research, what recommendations would you make to policymakers and healthcare systems regarding autism screening, diagnosis and support services?
- Discuss the limitations of this systematic review and meta-analysis. How do these limitations impact the interpretation and generalizability of the findings? What further research is needed to address these gaps?
