Robert Roos  News Editor

Mar 28, 2007 (CIDRAP News) – Hong Kong officials concluded that a baby girl who was recently infected with H9N2 avian influenza—a strain believed to have pandemic potential—probably contracted it from birds, according to recent reports.

A 9-month-old girl who was hospitalized with respiratory symptoms twice in recent weeks tested positive for an H9N2 infection Mar 20. The girl had only a mild illness but was treated in isolation at Princess Margaret Hospital, the Hong Kong Department of Health reported in a Mar 22 statement. At the time of her second hospitalization she had respiratory syncytial virus, the statement said.

Dr. Thomas Tsang, controller of the Hong Kong Centre for Health Protection, said tests had ruled out the possibility of human-to-human transmission in the girl"e;s case, according to a Mar 24 news release from Hong Kong"e;s Information Services Department.

Tsang said genetic analysis of the H9N2 virus showed that it was entirely of avian origin, suggesting that the child contracted it directly from a bird, the release said. Because the girl had no contact with wild birds before her illness, she may have caught the virus at a bird market that she visited several times with her family, Tsang said.

He also said tests on respiratory specimens from a healthcare worker and three children who were in the same hospital cubicle with the baby in early March tested negative for H9 viruses, and her family had no symptoms.

Meanwhile, leading virologist Robert Webster warned this week that H9N2 is an "insidious" virus that needs close monitoring because it could trigger an outbreak in humans, according to a Mar 27 Bloomberg News report.

H9N2 is far less known than the deadly Asian strain of H5N1 virus, which has killed at least 169 people and millions of poultry in Asia and Africa in the past few years. But Webster told Bloomberg, "H9N2 is an insidious virus. This is the one that"e;s far more dangerous in some ways. It doesn"e;t get much attention because it doesn"e;t kill chickens and doesn"e;t kill humans."

He said H9N2 can spread among pigs and infects chickens without making them sick. On the "hit list" of viruses, he added, "H5N1 is at [the] top, and H9N2 is right behind. Then come H7N7 and H2N2."

At least three cases of H9N2 illness, all of them mild, have occurred in Hong Kong children in recent years. Two girls were infected in 1999 and a 5-year-old boy had the virus in 2003.

Robert L. Atmar, MD, a Baylor College of Medicine professor who has participated in clinical trials of an H9N2 vaccine, said human H9N2 illnesses may be less rare than the record suggests. Seroprevalence studies in China in the 1990s found H9 antibodies in 2% to 3% of the population, which suggests that some cases are missed, he told CIDRAP News via e-mail.

Atmar, a professor in the Departments of Medicine and of Molecular Virology and Microbiology, also commented that the finding of a case in a 9-month-old child was "a little surprising unless she was toddling around the market. Usually, cases of avian influenza have followed close contact with infected poultry. H9N2 viruses are common in bird markets."