Data: The Center for Systems Science and Engineering at Johns Hopkins; Map: Andrew Witherspoon/AxiosFive Americans — all who traveled in Wuhan, China, and are now in California (2), Arizona, Washington state, and Chicago — have the novel coronavirus that's been spreading from China, the Centers from Disease Control and Prevention said Sunday. Why it matters: "We need to prepare as if this is a pandemic, but we hope it is not," said Nancy Messonnier, director of CDC's National Center for Immunization and Respiratory Disease."The risk to Americans is low at this time but the threat is serious and the public health response is aggressive."The latest: While U.S. public health officials have seen no evidence that the virus is infectious before a person shows symptoms — something that would likely call for stronger screening programs — they are investigating reports from two recent studies that point to that possibility.By the numbers: There are 100 people under investigation in 26 states, Messonnier says. Out of these, 25 so far have tested negative. Right now, the U.S. cases appear to have direct contact with Wuhan, she adds."We expect there to be additional cases of coronavirus in the United States," she says.The CDC plans to update its numbers on Monday, Wednesday and Friday.All of the five patients are hospitalized and "we are actively investigating close contacts," she adds.What's next: Public health officials are working to develop specific diagnostics, therapies and vaccines for this particular virus. They've isolated the genetic sequence from the first patient in the U.S. and are comparing this to the first patient found in China to see how it's evolving. Background: Coronaviruses are zoonotic, which means they can transmit from animal to human and then have the ability to evolve so they can transmit between humans. They range in severity from causing the common cold to deadly diseases like SARS and MERS.SARS, or Severe Acute Respiratory Syndrome, was believed to have originally transmitted from civet cats to humans, although recent genetic testing shows bats are the natural hosts. It was first reported in China in 2002 and recognized as a global threat in 2003, resulting in 774 deaths and serious economic impact. It mysteriously disappeared, for now.MERS, or the Middle East Respiratory Syndrome, is believed to have originally transmitted from dromedary camels to humans. It was first reported in Jordan and Saudi Arabia in 2012, had two U.S. cases in 2014, and it continues to circulate mostly in the Middle East where the CDC is monitoring it.Go deeper:U.S. evacuates personnel as coronavirus death toll climbsWHO: The coronavirus outbreak is not yet a global emergency U.S. to begin airport screening for new China virus as concerns growEditor's note: The map headline was corrected to show the date was as of Jan. 26, 2020 (not 2019).