US President Barack Obama responded to the first domestic emergency of his presidency by reassuring Americans it was "not a cause for alarm," even as his government began urgent steps to respond to the small-but-rising number of cases. The administration sent top health and homeland security officials out for televised briefings Monday on what was being done and promised they would keep coming back until the situation settled down. Obama inserted his own assurances in a previously scheduled speech, knowing the TV networks were waiting for his comments. Homeland Security Secretary Janet Napolitano said the government was preparing as if the outbreak would become the pandemic many fear, dispatching people and equipment to affected areas and stepping up information-sharing at all levels of government and with other nations. People were checked but not stopped at the borders and airports. Richard Besser, the acting director of the Centers for Disease Control and Prevention, said his agency was investigating aggressively, looking for evidence of the disease spreading and probing for ways to control and prevent it.