He found out he had been infected with a rare strain of hepatitis C through a letter from the Red Cross.

The Utahn had been a regular blood donor. But the letter informed him he was banned from donating in the future.

“I was horrified,” said the man, who was identified in federal court Monday only as “Patient Zero.”

Then the health department began calling, asking probing questions about his sex life and whether he used drugs, as officials tried to unravel how he got the disease.

It turns out this man and six others contracted hepatitis C after going to an emergency room. Their nurse, Elet Neilson, took portions of their pain medications and, in doing so, unknowingly infected them.

“I’m not a vindictive person,” Patient Zero said. “But I truly hope that people understand this recklessness can’t be tolerated. It really is a troubling thing to go through.”

U.S. District Judge Dee Benson sentenced Neilson to five years in federal prison. He knew that Neilson didn’t try to infect people, he said, but time behind bars was warranted.

“This is a case of unintended consequences,” the judge said. “No one has showed me any facts that the defendant intended to transmit a serious disease. It did happen. And that makes this case a remarkably sad one.”

Neilson, 53, pleaded guilty in September to two counts of tampering with a consumer product and two counts of fraudulently obtaining a controlled substance. A dozen similar charges were dismissed as part of the deal.

The plea deal allowed Benson to sentence her to as many as 10 years in prison. Federal prosecutor Sam Pead had asked Benson to sentence Neilson to more than seven years behind bars. Neilson’s attorney, Adam Bridge, argued for probation.

Neilson has until March 2 to turn herself in to federal authorities.

The former nurse gave a teary apology, telling the judge that she was “repulsed by my own behavior” and never thought her actions would affect so many people.

Neilson said she turned to drug use in 2014 as a way to cope with life. She was in the middle of a divorce, working long overnight shifts and caring for her young son, who has autism. Her son, she said, had lit her home on fire and they were living in a hotel room.

She didn’t know she had hepatitis C — or that she had infected her patients — until the Utah Department of Health called her in 2015.

“I was ravaged with guilt, shame, sickness,” she said. “When I saw and understood through the media that seven other people had the same strain that I did, I was devastated and sickened. I didn’t want to crawl out of my house. I didn’t want to be seen in public. I was physically sick.”

Neilson said she cried as she read the letters that her one-time patients had sent to the judge, which told stories of how her actions impacted them.

They wrote about how they had to endure a three-month treatment plan that produced painful side effects and caused some to hallucinate. They experience shame when they tell people they have contracted the disease. They worry about their families and their futures, about whether mixing toothbrushes or getting a paper cut could infect their loved ones. Some worried about whether it would affect intimacy with their spouse. Others became resigned to never finding a partner.

“The people she affected are real people,” said Patient Zero, “and we have real lives.”

Neilson admitted in plea agreement documents that when she was an emergency room nurse at McKay-Dee Hospital in Ogden, she took painkillers meant for patients and used it for herself.

Her attorney explained that Neilson would fill two syringes with pain medication and administer one to the patient and put the other in her pocket to use when she got home. She would then bring the needle back to work and get more medication. In the chaos of the emergency room, he said, the syringes got mixed up.

Though Neilson pleaded guilty to infecting seven patients, the Utah Department of Health estimated that at least 16 people were infected with the disease. State officials estimated that the former nurse exposed as many as 7,200 patients to the hepatitis C genotype B strain.

Of those patients, roughly 4,800 were treated at McKay-Dee Hospital — where Neilson worked from June 2013 to November 2014 — and 2,369 were at Davis Hospital and Medical Center, in Layton, where Neilson worked between 2012 and 2014.

Neilson admitted to taking drugs from her employer while working at both hospitals, according to Utah Division of Occupational and Professional Licensing records. She surrendered her nursing license in November 2015, a month after health officials began offering free testing to the thousands of patients who came into contact with her at the two hospitals and were given certain medications.

This is the first time federal prosecutors in Utah have taken on a case like Neilson’s. Similar cases have been reported nationwide, including a case of a traveling radiology technician who infected 30 patients with the virus in a multi-state outbreak. That technician was sentenced to serve 39 years in federal prison after pleading guilty to 14 charges similar to Neilson’s.