On Saturday, the Mexican government was encouraging migrants to leave a large encampment in the border city of Matamoros, where some 2,000 have been living in tents on a muddy strip of land next to the international bridge.

At least 150 migrants boarded buses at the camp on Saturday and were taken away, though it was unclear whether that was related to the coronavirus. From time to time in recent months, the federal government has provided bus service to migrants seeking to leave northern Mexico and return to Central America.

Mexican officials said the buses on Saturday were provided by the government in response to requests from migrants living at the camp.

Friday’s decision by the Trump administration to wall off the border from potential infections seems, for the moment, to fly in the face of transmission patterns.

Helen Perry, executive director of Global Response Management, a nonprofit that runs a clinic at the migrant encampment in Matamoros, said there had been no transmissions of the virus among the migrant population so far, and none of those residing in the camp appeared to show symptoms.

Similarly, in Tijuana and Ciudad Juárez, medical professionals reported no suspected cases.

Meanwhile, the number of confirmed cases in the United States dwarfs those in every nation in Latin America and the Caribbean, combined.