There's a correlation, but not a causal link.
For example, lets say... A certain virus, that has a fever and headache as a symptom. If a pregnant woman contracts said virus, she likely will take acetaminophen for it.
Now, let's also say, that particular virus can cause the markers responsible for autism to activate.
So, since the virus is unknown, the only correlation we see is the acetaminophen use, while pregnant.
Did the unknown (yet) virus cause it, or did the acetaminophen use cause it?
All people with autism, also had mothers who consumed water during their pregnancy... Did water cause autism?
At this point, it's almost a certainty that this is the case, possibly activated by environmental influences during pregnancy. However, none of the influences have been identified, as there's (Last I looked) about 30 separate DNA sequences that are related to autism in people.
For what it's worth... there's about the same number of DNA sequences involved in someone requiring corrective lenses.