Why does Amtrak have to pay attention to ventilation?

www.railwaygazette.com

In Japan, commuter trains are still running as usual, except for Nishitetsu on weekends. But, no patient infected on train is reported. That must be achieved by ventilation and frequent opening of doors. On the other hand, most of the trains operated by Amtrak are running with few stops. It means they have less opportunity to open doors. So, Amtrak will have to pay attention to ventilation like opening windows, while running between stations with long distance.