The Department of Public Reassurance

If you are confused about the significance of symptomless cases of H5N1 infection, this is not surprising given the variety of messages coming from Vietnam, WHO and flu experts. Here is Voice of America reporting on Hanoi-based WHO epidemiologist Peter Horby:

A researcher with the World Health Organization says people who test positive for bird flu but have no symptoms of the disease may be contagious, but probably pose a lower risk of transmission to others.

Peter Horby, an epidemiologist based in Hanoi, made the comments a day after the grandfather of two bird flu patients tested positive for the virus, despite never falling ill.

Here is an interview with Horby from Reuters:

"In most infections, or many infections, it is not unusual to get people who have either mild or asymptomatic infections," Hanoi-based WHO medical epidemiologist Peter Horby told Reuters.

"There is no evidence that asymptomatic infection like this poses any significant risk of onward transmission, so it is not alarming in that sense," he said.

This is reassuring. On the other hand, we read this from the AP (via CBC):

A string of bird flu infections in northern Vietnam involving several families has raised troubling questions over whether the deadly virus that has killed 46 people in Asia may be changing, health experts said Thursday.

Six of the last seven cases confirmed in the past couple weeks are from northern Thai Binh province and are connected to two families - with some relatives showing no symptoms of the disease. Health experts are unsure whether the new cases signal the possibility that the virus is slowly transforming to allow human-to-human transmission or just underscore more careful detection.

"Certainly, it calls for investigation. It's too early to say whether these cases are any different from previous cases or not," said Dr. Peter Horby, a Hanoi-based epidemiologist for the World Health Organization.

"The two people with atypical infections could be related to improved testing, or it could relate to some difference in the virus. We won't know till we isolate the virus. It's too early to be raising alarms," he said, referring to the two latest cases.

In those cases, an 80-year-old man, whose two grandchildren are hospitalized with the bird flu, and a 61-year-old woman, whose husband died from the disease, both tested positive for the H5N1 virus but showed no signs of illness.

The mild or even symptomless infections raise the possibility that the H5N1 virus is changing, and that there may be more undetected cases.

"Undoubtedly, there are more cases than those we detect . . . I'm sure there's cases we're missing," Horby said.

Hmm. What do other flu experts think (KeralaNext)?

The H5N1 bird flu virus might be acquiring a greater ability to spread from human to human, recent cases in Vietnam suggest. But as two elderly relatives of patients killed by the bird flu test positive for the virus and yet have no symptoms, there are also indications that it may not be as lethal as currently thought.

The 2004 outbreak of H5N1 in Vietnam stopped in spring after the country killed millions of infected and exposed poultry. But outbreaks resumed in December, probably because the virus persisted in ducks showing no symptoms, say flu experts. Since December, 22 people have tested positive for H5N1 in Vietnam, of whom 14 have died, including one woman from Cambodia.

Five of the cases occurred in clusters that suggest the virus passed from person to person. In the most recent, a 14-year-old girl fell ill on 14 February, her 21-year-old brother on 21 February, and a 26-year-old male nurse who cared for the brother, on 26 February.

Spread of the virus to health care workers would be worrying, says leading flu expert Robert Webster at the St. Jude Children's Research Hospital in Memphis, US. Attending a conference on microbial threats in Lyon, France, last week, he told New Scientist: "That's where we'd expect to see the first cluster if this virus starts spreading among humans."

So here is how I read it. Dr. Horby may express confidence asymptomatic cases represent no threat, but there are enough uncertainties here to suggest his expression of confidence may indicate he sees himself as working for the World Reassurance Organization, not the World Health Organization.

Not very reassuring.