U.S. health officials are currently monitoring 110 people across 26 states for the coronavirus, including the five patients who contracted the deadly infection in China and brought it back to America.
The disease, which has killed at least 81 people in China and sickened more than 2,800 worldwide, isn't spreading within the community in the U.S. and the risk to the public right now is still considered low, Dr. Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases, told reporters on a conference call Monday.
"We understand that many people in the United States are worried about this virus and how it will affect Americans," Messonnier said. "Every day we learn more, every day we assess to see if our guidance or our response can be improved."
The number of "patients under investigation" in the U.S. has almost doubled from the 63 the Centers for Disease Control and Prevention said were under surveillance on Thursday. The CDC says 32 people have tested negative for the virus.
"While that number is 110, we are certainly prioritizing based on [patients under investigation] that might be at higher risk," Messonnier said.
The CDC confirmed Sunday a fifth U.S. case of the virus — a patient in Maricopa County, Arizona, who recently traveled to Wuhan, China, the epicenter of the disease's outbreak and where the majority of cases have been reported.
Messonnier said the CDC has screened roughly 2,400 people flying from Wuhan to five major U.S. airports and is considering expanding its screening. The agency increased its travel warning for all of China, asking people traveling to practice "enhanced precautions."
"This outbreak is unfolding rapidly and we are rapidly looking at how that impacts our posture at the border. We're certainly considering broadening of that screening," she said.
Coronaviruses are a large family of viruses that usually infect animals but can sometimes evolve and spread to humans. Symptoms in humans include fever, coughing and shortness of breath, which can progress to pneumonia. Physicians have compared it to the 2003 outbreak of SARS, which had a short incubation period of two to seven days.
China's National Health Commission minister, Ma Xiaowei, said on Sunday that the incubation period could range from one to 14 days, and the virus was infectious during incubation, unlike the outbreak of severe acute respiratory syndrome, Reuters reported.
On Monday, the CDC said it hasn't seen "any evidence of patients being" infected "before onset."
Messonnier said the incubation period for the new virus is somewhere between two and 14 days. There's been some debate over how contagious the disease is and she said it may not be known for a while.
"This outbreak is really unrolling in front of our eyes," she said.
The so-called R naught, a mathematical equation that shows how many people will get an illness from each infected person, is somewhere around 1.5 to 3, she said. Measles, which is one of the most contagious infections in the world, has an R naught of around 12 to 18, by comparison, she said.
The CDC is trying to speed up testing and to get the tests in the hands of state health officials. It currently takes the CDC about four to six hours to make a diagnosis once a sample makes it to its lab.
U.S. health officials have warned that the flu or other respiratory illnesses could complicate identifying more cases. They recommend that people call a health-care provider before seeking treatment so the appropriate measures can be put in place.
In China, some 50 million people are now under travel restrictions. Shanghai Disney is closing until further notice at a time when the theme park would normally be packed with tourists during the Lunar New Year holiday. Starbucks and McDonald's also closed stores in Hubei province where Wuhan is located.
The WHO's director-general, Dr. Tedros Adhanom Ghebreyesus, is traveling to Beijing to meet with government and health officials. According to the organization, more data needs to be collected before the virus, which can spread through human-to-human contact, is declared a global health emergency. The WHO declined at two emergency meetings last week to say it was a worldwide emergency.