Federal authorities are tracking the spread of a mysterious virus that has traveled from China to the United States. Though stateside risk is currently low, older adults are among those most vulnerable, reports the Centers for Disease Control and Prevention.

In response, the CDC this week released interim guidance for healthcare professionals who may encounter patients with symptoms related to the illness, provisionally called the 2019 Novel Coronavirus. These include fever and acute respiratory signs such as cough and difficulty breathing.

The virus originated in the Chinese city of Wuhan, causing a pneumonia outbreak there that’s steadily growing. The virus has since spread to at least five other countries. The United States reported its first case, in Washington state, on Tuesday.

Coronaviruses pose the most danger to older adults, people with cardiopulmonary disease, those with weakened immune systems, and infants, according to CDC officials.

While little is yet known about the virus, “the immediate health risk from 2019-nCoV to the general American public is considered low at this time,” the agency stated on Tuesday. Nevertheless, it is urging care providers to be on the lookout for patients with respiratory symptoms and a history of travel to Wuhan, or close contact with someone who may have traveled there recently.

At press time Wednesday, the Chinese government had locked down the city of Wuhan, preventing travel in and out, according to various news outlets.