The novel coronavirus has spread to at least 34 states in the U.S. and Washington, D.C., and each official who has confirmed cases in their home state has warned that more illnesses are likely to come, especially as more test kits are made available.

“The outbreak is entering a new phase, from mostly travel-related cases to domestic transmission,” Dr. Robert Amler, dean of the School of Health Sciences and Practice at New York Medical College and former Centers for Disease Control and Prevention (CDC) chief medical officer, told Fox News. “This puts our preventative measures to the test – how good a job can every one of us do to minimize the spread of the virus?”

CORONAVIRUS: WHAT YOU NEED TO KNOW

On Monday, the CDC said none of its employees had tested positive for COVID-19, but discussed a series of guidelines for those who are considered to be most vulnerable to the virus, including the elderly and those with weakened immune systems.

Dr. Nancy Messonnier, CDC director of the center for the National Center for Immunization and Respiratory Diseases, said the guidelines include avoiding large gatherings, staying close to home, and stockpiling medications and groceries. In addition, caregivers should devise a plan for how to provide care for patients should they contract the illness.

“As the trajectory of the outbreak continues, many people in the U.S. will at some point in time this year or next be exposed to the virus, and there’s a good chance many will become sick,” Messonnier said.

CORONAVIRUS IN THE US: STATE-BY-STATE BREAKDOWN

She also asked for people to understand the need for “personal responsibilities” to protect those who are older and considered at risk for complications and to listen to local government officials regarding event cancellations and other guidance.

“We’re looking both at risk of exposure and risk of the individuals,” she said.

Some of those responsibilities include using good personal judgment before traveling.

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“Domestic travelers should use good judgment,” Amler said, “considering the importance of the trip and the expected level of virus activity at the destination.”

As far as mass transit goes, Amler said the risk of boarding buses and trains each day is “not well characterized” yet, but for riders and those who must continue commuting, “the basic rules always apply – social distancing and avoidance of contact with people who are coughing, sneezing, etc.”