(AP) - Minnesota health officials are investigating the death of a person who was infected with a strain of the polio virus.
The patient was infected with the live polio virus that was used in the oral vaccine, which was discontinued in the U.S. in 2000, the Department of Health said Tuesday.
The vaccine now in use is injected and doesn't contain live virus, and officials said this case poses no risk to the general public.
"This is a very rare occurrence and does not signal a resurgence of polio," State Epidemiologist Ruth Lynfield said in a statement.
The patient died last month with polio symptoms that included paralysis, but the department said it's not known to what extent polio contributed to the death.
The patient also had a weakened immune system and multiple health problems. It's likely the patient became infected from someone who had received the live-virus vaccine before its use was stopped, the department said.
The department said it was working to determine if any health care workers might have been exposed. It said only unvaccinated people or people with deficient immune systems who had direct, ungloved contact with the patient's bodily secretions would be at any risk.
Citing patient privacy laws, the department did not release any details about the victim.
Officials said this type of polio infection is very rare. Only 45 cases of vaccine-derived paralytic polio disease in people with immunodeficiencies have been reported in the world since 1961, according to the Centers for Disease Control and Prevention.
In these rare cases, the health department said, someone who has either never been vaccinated or has a weak immune system can get the polio virus from someone who has been vaccinated and is excreting the virus in their stools.
Sometimes, but not always, these infections result in illness, as happened in this case.
The other reported U.S. instances of vaccine-derived polio infection also occurred in Minnesota, in 2005. Five children from the Amish community near Clarissa in central Minnesota, which had low rates of immunization, were infected but did not develop outward symptoms.
Lynfield said they suspect the reason all the U.S. cases were detected in Minnesota was because of its advanced public health reporting system.
The CDC says the oral vaccine is still used in countries where naturally occurring polio is still a threat because it's better at stopping the spread of the virus.
The U.S. switched to the injected vaccine because wild polio has already been eliminated from the Western Hemisphere, and the few cases of polio that were occurring, about 8-10 per year, were caused by the oral vaccine itself, not the wild virus.
The last case of naturally occurring paralytic polio occurred in the U.S. in 1979, but health officials said the new case was a reminder for people to make sure their immunizations and their children's shots are current.
Most people in the U.S. have been vaccinated against polio.
(Copyright 2009 by The Associated Press. All Rights Reserved.)