According to researchers at the U.S. Centers for Disease Control and Prevention (CDC) in Atlanta, the first-ever national estimate of the prevalence of autism in the United States has found that the disorder affects up to one in every 175 school-age children.
This says the CDC equates to at least 300,000 U.S. schoolchildren with autism, a condition that causes difficulties with learning, socializing and behavior.
The agency's figures are based on interviews conducted in 2003 and 2004 with the parents of nearly 98,000 children aged 4 to 17.
The results of two national surveys, the National Health Interview Survey (NHIS) and the National Survey of Children's Health (NCHS) indicate that at least 5 in every 1000 children of school age are diagnosed with autism.
Laura Schieve, an epidemiologist with the CDC's National Center on Birth Defects and Developmental Disabilities (NCBDDD) says the ratios correspond to about one in every 175 -181 children.
Schieve says as shown in previous studies, boys are nearly four times more likely to have been diagnosed with autism than girls.
The CDC says the surveys confirm that autism is a condition of major public health concern that affects many families, and supports previous estimates of autism, which were based on local surveys done in Atlanta and New Jersey.
Laura Schieve, an epidemiologist at the National Center on Birth Defects and Developmental Disabilities who helped conduct the study said however it could not answer many questions about autism.
The CDC experts emphasise that the results do not reflect on either the underlying causes of autism, or ongoing prevalence trends.