Autism is a life-long neurodevelopmental condition interfering with the person's ability to communicate and relate to others. Since the earliest epidemiological surveys in the 1960s, a wealth of data has become available, indicating a much higher prevalence of the condition than previously thought [Fombonne, 2003a, 2005; Fombonne, Quirke, & Hagen, 2011]. It is now recognized that some individuals with the condition are able to lead independent and fulfilling lives, whereas for others the impact can be severe, interfering significantly with quality of life [Farley et al., 2009]. While the global burden of autism is currently unknown, in the United States and in the UK, the annual societal cost of the condition exceeds several billions [Ganz, 2007; Knapp, Romeo, & Beecham, 2007].
Increased recognition, understanding, and awareness of autism in the last few decades have been, in part, driven by the significant growth in research evidence. While many aspects of autism remain poorly understood, major advances have been made in terms of highlighting the genetic [Abrahams & Geschwind, 2008], biological [Belmonte et al., 2004], environmental [Currenti, 2009], and developmental [Elsabbagh & Johnson, 2010] origins of the condition. Large-scale and well controlled cohort studies (e.g., http://www.earlistudy.org) following-up pregnant mothers are likely to clarify the effects of some pre- and perinatal risk factors implicated in autism. Significant strides have also contributed towards developing and validating screening and diagnostic instruments, helping to reduce heterogeneity in clinical characterization in research studies. While some of these diagnostic tools remain highly resource intensive, they are increasingly used in clinical settings, as they provide rich and systematic information to inform service provisions where those are available. However, even in high-income countries, provisions for screening, diagnosis, and intervention are highly variable and many cases absent in community settings.
Such advances in autism research have contributed towards bridging the gap between evidence and practice in some countries, but there is little systematic information available with regards to the impact of the condition on most of the world's population. Frequently regarded as essential for advancing basic research and strategic for informing policy and developing services, epidemiological studies have emerged as a clear priority within several global initiatives. The charity Autism Speaks in partnership with the US Center for Disease Control (CDC) launched the International Autism Epidemiology Network (http://www.autismepidemiology.net), bringing together researchers worldwide and focusing specifically on service improvements in developing countries. According to the network, prevalence studies for PDD are ongoing in Australia, Mexico, Finland, Portugal, Iceland, India, Vietnam, Taiwan, South Africa, and Uganda. Focusing on a broader context than autism, the Movement for Global Mental Health has identified a clear treatment gap, particularly pronounced in low- and middle-income countries [http://www.globalmentalhealth.org; Patel et al., 2008]. Epidemiological data on the burden of mental and neurological disorders and systematic mapping of relevant services in low- and middle-income countries encouraged World Health Organization (WHO) to launch the mental health Gap Action Programme (mhGAP) [WHO, 2008]. Moreover, the Global Alliance for Chronic Disease, which groups several agencies including Australia's National Health Medical Research Council, the Canadian Institutes of Health Research, the Chinese Academy of Medical Science, the UK's Medical Research Council, and the United States' National Institutes of Health, announced a program to identify the world's “Grand Challenges in Global Mental Health” (http://www.grandchallenges.org). The reasons for why epidemiological surveys are viewed as a priority extend beyond the need for objective and robust estimates of prevalence. These provide additional valuable benefits as they often result in systematic information regarding existing services and may help in assessing the needs and priorities for each community. In the long run, the availability of comparable estimates from different geographic regions may also enable testing challenging hypotheses regarding the etiology of PDD.