A person with the mumps infects 10 other people, on average. Even HIV and SARS are twice as contagious, on average, than Ebola, with a so-called R0 rate of 4. The R0 rate measures how many other people an infected person infects.
Ebola's R0 rate is similar to that of Hepatitis C, which has a rate of 2.
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NPR notes that Ebola's relatively low rate likely stems from the fact that people who are infected need to have had close contact with others through bodily fluids, to spread the virus.
In countries with poor health systems, like those in West Africa, Ebola has spread quickly, despite the low R0 rate, and killed an estimated 70 percent of those infected in that epidemic.
So far, just one person has been diagnosed with Ebola after traveling to the U.S., Thomas Eric Duncan, who is currently hospitalized in Dallas. Officials on Friday said 50 people who may have had contact with Duncan are being closely monitored, including several relatives of his in Dallas, who are under quarantine.
Officials also are investigating whether two other people in the U.S., one in Washington, D.C.., and one in Georgia, are infected with Ebola.
Read the NPR story here: "No, seriously, how contagious is Ebola?"