The State Department and the Centers for Disease Control and Prevention (CDC) are advising travelers to China to “exercise increased caution” due to the outbreak of the coronavirus that originated in Wuhan.

According to the travel advisory, anyone who has traveled to Wuhan and feels sick should seek medical care right away. It also urged people to call ahead to the doctor’s office or emergency room to tell them about the recent travel and any symptoms.

The agencies are urging Americans to avoid nonessential travel to Wuhan. Chinese officials have closed transport into and out of the city of 11 million, including buses, subways, trains and the international airport.

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The virus was officially detected in the United States for the first time last week after infecting more than 500 people in China and killing at least 17 people. The risk to the broader American public is low, but the situation is still evolving.

The outbreak is thought to have originated in a Chinese seafood market in early December, and it continues to expand in scope and magnitude.

The CDC said it expects more cases to be confirmed. Person-to-person spread is occurring, though it’s unclear how easily the virus is spread between people.

The World Health Organization is expected to decide today whether to declare a public health emergency.

However, while there are still many unknowns about the virus, officials are stressing that other diseases are far more deadly. The CDC said the flu virus that circulated around the world last year killed an estimated 57,000 Americans.