May 16, 2006 (CIDRAP News) – Researchers in Thailand recently reported that they isolated live H5N1 avian influenza virus from the blood of a 5-year-old boy, an unusual finding that raises concern about possible transmission of the virus via blood.
Pieces of H5N1 virus RNA have been detected previously in human blood, but live virus had not been recovered before, experts say. The Thai researchers reported that they cultured the virus from blood samples of a boy who died in December 2005. Their report was published online recently by Emerging Infectious Diseases.
"This case showed the virus in the patient's blood, which raises concern about transmission among humans," says the article by authors from two universities and the Thai National Institute of Animal Health, all in Bangkok. Salin Chutinimitkul of Chulalongkorn University was first author of the report, scheduled for publication in the journal's June issue.
The boy in the study was the last patient in the three waves of human H5N1 cases in Thailand to date, according to the report. He fell ill Nov 28, 2005, and died Dec 7. Plasma from a blood sample taken the day of his death tested positive for the virus by polymerase chain reaction.
Plasma from the patient was injected into an embryonated chicken egg, the report says. The embryo died within 48 hours, and the allantoic fluid was found to contain H5N1 virus.
Influenza viruses normally affect exclusively or primarily the respiratory system. The authors say it is unusual to find live influenza virus in human serum or plasma, but they cite two previous examples, dating to 1963 and 1970. In addition, in a case reported in 2005, H5N1 fragments (RNA) were found in serum from a Vietnamese boy who died of H5N1 infection after having gastrointestinal and neurologic signs and symptoms.
Because probable human-to-human transmission of H5N1 has been reported at least once, "This case should be a reminder of the necessity to carefully handle and transport serum or plasma samples suspected to be infected with H5N1 avian influenza," the report states.
In addition, the finding suggests that blood samples from suspected H5N1 patients should be handled and tested in biosafety level 3 (BSL-3) laboratories to protect workers, the authors write.
Matthew Kuehnert, MD, assistant director of blood safety at the Centers for Disease Control and Prevention (CDC) in Atlanta, agreed that finding live flu virus in blood is unusual. "But it's pretty unusual for someone to even look. That's the caveat there," he told CIDRAP News.
Given the previous report of H5N1 RNA in blood, the virus's presence in blood "is not a new concept," he added. "But I believe this is the first time someone has taken the extra step and successfully cultured live virus out, or shown that there's live virus in the blood."
Calling the finding "important," Kuehnert added, "We don't know what it means as far as pandemic flu is concerned because we don't know what the strain is going to look like, whether it'll look like this [H5N1] or something different."
The report also implies a possible risk to the blood supply if the H5N1 virus evolves into a human pandemic. Kuehnert said more needs to be learned about the extent of the viremia.
"In this letter [report], they took plasma from the patient when he had severe pneumonia; that's not something that someone is going to walk into a blood center with," he said. "The question is whether it's present when a patient is symptomatic or convalescent." Similar questions arose with West Nile virus, which turned out to be detectable in blood before and for a while after symptoms, he added.
To answer the question will require tests on groups of people exposed to H5N1, Kuehnert said.
A laboratory manager and an infection control expert both downplayed the idea that the finding suggests a need for new biosecurity or infection control precautions in dealing with possible H5N1 cases.
"This doesn't change anything, in my opinion," said John Besser, MPH, director of the clinical laboratory at the Minnesota Department of Health in St. Paul. "In the microbiology world we use universal precautions, we treat everything like it's dangerous."
Besser said BSL-2 precautions are recommended in the United States for ordinary testing of blood and other specimens from suspected H5N1 patients. However, the CDC recommends using enhanced BSL-3 precautions when culturing samples from suspected H5N1 patients, he added.
Jeanne Pfeiffer, RN, MPH, of the University of Minnesota School of Nursing in Minneapolis, said the report doesn't suggest to her a need for enhanced clinical infection control practices. "With the handling of blood we always use standard precautions. The precautions we have now would protect us from any unknown virus or pathogen in blood, ever since AIDS," she said.
"The assumption is that every patient has a chance of being infectious with a bloodborne pathogen, so we always use gloves," Pfeiffer added. She is a teaching specialist and content expert for the Minnesota Emergency Readiness Education and Training (MERET) grant.
Chutinimitkul S, Bhattarakosol P, Srisuratanon S, et al. H5N1 influenza A virus and infected human plasma. Emerg Infect Dis 2006 Jun;12(6) (early online publication) [Full text]
CIDRAP information on infection control guidelines for H5N1 avian influenza