Evidence for a gastrointestinal route for human avian influenza infection should be interpreted cautiously, according to Dr. William Schaffner, chair of the department of preventive medicine at Vanderbilt University in Nashville, Tenn.
As the H5N1 virus continues its global march amid fears that it may mutate to become more easily transmissible, a study published last year suggesting a gastrointestinal portal is getting renewed attention.
Last year, Dr. Menno D. de Jong, head of the virology department at the Oxford University Clinical Research Unit in Ho Chi Minh City, Vietnam, published a case report of a child who died of avian influenza after an atypical gastrointestinal presentation, fecal evidence of the H5N1 virus, and no respiratory symptoms at presentation (N. Engl. J. Med. 2005;352:686–91).
This case and several other published reports suggest that the gastrointestinal tract may also be vulnerable to the infection, Dr. de Jong was reported as saying.
“The presence of viable virus in the feces of our patient has important implications for transmission, infection control, and public health,” Dr. de Jong and his colleagues wrote. This “highlights a potential route of human-to-human transmission, especially in combination with crowded living conditions and diarrhea.”
To date, experts consider human-to-human transmission of avian influenza very rare, but they agree that if the H5N1 virus becomes easily transmissible among humans, it likely would trigger a global pandemic. Recent studies have suggested that the preferential attachment of the virus to cells in the lower rather than the upper human respiratory tract may explain why it is not easily spread by coughing and sneezing (Science 2006;312:399). But the possibility of gastrointestinal infection suggests the potential for much easier fecal-oral transmission.
Dr. Schaffner, who is also professor of medicine in the division of infectious diseases at Vanderbilt, says a couple of isolated reports of gastrointestinal evidence of the H5N1 virus should not cause alarm. “There is nothing we know about the general epidemiology of influenza that would suggest this is a form of transmission that is in any way noteworthy, although we should keep an eye on it,” he said in an interview.
A similar gastrointestinal presentation, with diarrhea as the initial symptom and with no respiratory illness, has been described elsewhere (Emerg. Infect. Dis. 2004;10:1321–4), Dr. de Jong said in an interview, and other researchers have also documented intestinal replication of the H5N1 virus in humans (Emerg. Infect. Dis. 2005;11:1036–41).
In addition, there are reports of human infection in which patients' only exposure to the virus was through the consumption of duck blood or undercooked poultry, Dr. de Jong said (N. Engl. J. Med. 2005;353:1374–85).
“The spectrum of influenza H5N1 is wider than previously thought,” he wrote. “Clinical surveillance of influenza H5N1 should focus not only on respiratory illness, but also on clusters of unexplained deaths or severe illnesses of any kind.”
Dr. Schaffner said that even if gastrointestinal infection is shown to be more common than previously thought, preventive measures are already being taken.
“We already have one public health response that works well for both respiratory and intestinal infections,” he said. “Hand washing is one of the most effective ways to interrupt intestinal transmission of known viruses and bacteria that are spread in stool.”
This limited gastrointestinal evidence of the H5N1 virus should not cause alarm, but 'we should keep an eye on it.' DR. SCHAFFNER