<p>Mexican ambulance drivers are transporting hospital patients unable to pay for medical care or emergency-room services in their country to facilities in the United States, where their treatment is mandated by federal law, authorities said yesterday.</p>
<p>The border crossings have been reported from Brownsville, Texas, to Douglas, Ariz., and involve Mexican ambulance companies whose drivers have been instructed by hospital officials in Mexico to take ailing and uninsured patients to the United States, the authorities said.</p>