Oh yes, health-visitors, I have come across some terrible ones. I don't think the majority of them read anything, except their little red/vlue books and weight/height charts.
When my ds3 was sat in a corner rocking back and forth, staring at string when he was 20 months old, the health visitor said he was concentrating on something for so long he couldn't possibly be autistic. He will soon start babbling, and to enjoy the peace.
It took 6 months from that point to finally get a diagnosis, and then a second opinion, from respected developmental paediatrician to get the correct one.
My ds2 as diagnosed within 4 months, but not until 5 years old.
They were both certainly different from birth, and did the staring out of the corner of the eye, and spinning of everything. Ds4 is two next week, and spins objects, he is verbal, but not picking up words at the rate of other children his age. He also has alot of problems with pronunciation, and has words for things that only I understand. Such as 'kookoo' for train, 'nana' for thomas the tank engine, 'mimi'for biscuit, etc. He has just started pointing at things he wants, but prefers to move my hand. I am watching him for signs, as is my ds3's doc.
He is alot like ds3 at that age: angry, difficult, sleeps very poorly, and does like to throw things rather than play with them, he does the same action again and again for literally hours and goes wild if disturbed. Ds3 was very placid, and barely made a sound except a high pitched scream.