The connection was made after a Rhode Island Hospital doctor reported an unusual viral death. Health officials then traced the death back to the organ donor. Officials found her hamster at her home and the pocket pet tested positive for the virus.

"This is an unfortunate series of events," said Dr. Jay Fishman of Massachusetts General Hospital, who treated one of the organ recipients who died. "It's terrible for the patients and their families. These kinds of things happen, but it is very rare."

Four people -- two from Massachusetts and two from Rhode Island -- underwent transplant surgery on April 10 and 11 after receiving the organs from a woman who died from an embolic stroke.

The Rhode Island woman's organs were tested -- and cleared -- for several infectious diseases but not for lymphocytic choriomeningitis virus, or LCMV, a viral infection she got from an infected hamster she bought three weeks earlier at Petsmart in Warwick, R.I.

Doctors said the germ isn't normally tested for in organ transplants.

The woman's infected liver, lungs and kidneys were transplanted into four people who became critically ill. Three of them died within three weeks.

The dead include a liver recipient and a double-lung recipient from Massachusetts and a kidney transplant recipient from Rhode Island. The transplants were done at Massachusetts General Hospital, Brigham and Women's Hospital and Rhode Island Hospital, respectively.

The fourth person, who got a kidney at Rhode Island Hospital, was given an anti-viral drug and is recovering, officials said.

Two others received the woman's corneas and have been been asymptomatic, officials said.

The connection was made after a Rhode Island Hospital doctor reported an unusual viral death. Health officials then traced the death back to the organ donor. Officials found her hamster at her home and the pocket pet tested positive for LCMV.

The four recipients also tested positive for the rodent virus. The amount of virus in the donor was so low that the Centers for Disease Control and Prevention have not been able to identify the virus in her blood samples.

The tragic turn of events has touched off numerous investigations by several agencies. The CDC confiscated at least 60 hamsters, mice and rats from Petsmart and are trying to determine where the hamster picked up the virus.

The only other known incident of LCMV-infected organs causing a death occurred in Wisconsin in 2003.

Fishman said the MGH patient did well from the transplant surgery but developed liver failure before doctors learned the organs were infected.

Humans become infected with the virus when they come in contact with rodent urine, feces or saliva. In healthy people, LCMV usually only causes flu-like symptoms.

But organ recipients get drugs that suppress their immune system to help prevent organ rejection. The downside, officials said, is that they are more vulnerable to infectious disease.

Officials would not identify the donor or victims, citing privacy laws.