Public health officials have announced that the first patient to ever be diagnosed with Ebola in the U.S. is being treated at a hospital in Texas. But how do you actually test to see if someone has the virus? Thomas Ksiazek, a professor at UTMB who has done extensive research on Ebola, says that testing is done using a process called real-time RT-PCR, or reverse transcription polymerase chain reaction. In this technique, doctors or medical personnel take samples of blood from a patient. They then add an enzyme to convert RNA found in the blood into DNA (RNA is a chemical messenger that helps turn DNA’s “instructions” into proteins). Next, a “primer” is added that targets a string of genetic code unique to the Ebola virus. The concoction is then run through a PCR machine, wherein that strand of Ebola genetic material is amplified, or copied, many times (if it’s there, that is. If it’s not, nothing happens and the test returns a negative.) Finally, a chemical probe is added that binds to these snippets of DNA and alerts the scientists to the presence of the Ebola virus, Ksiazek tells Newsweek. The whole process can take as little as three to four hours.