Doctors are trying to determine how an Illinois man contracted Middle East Respiratory Syndrome, or MERS, from a Northwest Indiana patient after two brief meetings and a handshake. It's the third case of MERS is the United States, and the country's first transmission. Dr. LaMar Hasbrouck, with the Illinois Department of Public Health, says the new case changes their thinking on MERS somewhat. "That can mean at the end of the day," Dr. Hasbrouck said, "that this virus is more easily transmittable than we thought initially." The individual who was being treated for MERS in Lake County, Indiana, was released from Community Hospital in Munster May 9th and is considered to be fully recovered. Last week officials announced the second US case was discovered in Florida. "Every single case is different," said Dr. Hasbrouck. " It is a spectrum of possibilities and we're trying to learn as much as we can." The latest case involves an Illinois man who initially tested negative for the deadly respiratory virus, but a second test showed his body had actually fought the disease and won. ABC's Senior Health and Medical Editor Doctor Richard Besser has been talking to CDC doctors about what's next. "These are good signs but until you can be certain that that's the norm," said Dr. Besser. "That people can get this and have no problem whatsoever, they're going to be all over it and check every single case."