I was just going on known cases in my area. It was odd. About the time TM hit my wife GB hit two other persons and this was new to the Neurologist because it hadn’t shown up yet. GB like TM can be triggered by many sources but GB seems to be more linked to flu virus and flu vaccine. IOW a Flu exposure it seems could just as likely trigger it.
We had a cluster of Lou Gehrig’s Disease cases in my town around 1980. Very spooky, always makes you suspect that there is a common cause but I guess it was just a tragic coincidence.