Emily Anthes

Officials are exploring the possibility that a common adenovirus might be responsible for the unexplained cases, which remain rare.

The cluster is the first known instance of likely animal-to-human transmission in the United States.

The F.D.A. authorized a breath-based test made by a small Texas company, which said it hoped that mobile sites could use the device.

An increasing reliance on at-home testing and the closings of mass testing sites are making official case counts less reliable, scientists say.

Research on past conflicts suggests that the war in Ukraine could have a profound environmental impact.