Indonesia has confirmed H5N1 infection in the son of a woman who died last week of the virus. But the woman's husband, who was also under investigation, has tested negative for the avian flu virus, a top health ministry official said Sunday.
"Only the son is positive,'' said Dr. Nyoman Kandun, Indonesia's director general of disease control and environmental health.
"The husband is negative .... He will be discharged tomorrow or the day after tomorrow. He's all right now,'' Kandun said from Jakarta.
Kandun noted three sets of tests on the husband, 46, came back negative for H5N1. Several family contacts were also tested but are free of infection.
The son's test results confirm that Indonesia has experienced a new cluster of cases, the country's 10th according to statistics Kandun has compiled.
It was not immediately clear if there are any reasons to suspect human-to-human spread in this family or if both the son, 18, and his mother, 38, are thought to have been infected through exposure to diseased poultry.
In this cluster, as with the others, infection has only occurred among blood relatives _ not spouses, in-laws, friends or neighbours _ a fact that adds fuel to the theory that the unlucky few who have fallen ill have some genetic vulnerability to the virus. (There have been examples elsewhere, including Vietnam, where clusters involved family members not related by blood. But to date they have been more rare.)
Case clusters always grab headlines _ and the attention of scientists tracking H5N1's rare incursions into people. But experts insist some clusters are far more worrisome than others.
Each rates serious investigation, but not five-alarm status.
Dr. Tim Uyeki, an influenza expert with the U.S. Centers for Disease Control in Atlanta, closely tracks H5N1 cases.
Uyeki said somewhere between 20 and 30 per cent of the roughly 265 human cases that have been confirmed to date have happened in small clusters, generally numbering two or three people.
Of the 10 countries that have recorded H5N1 cases, all but one have seen case clustering. The exception is Djibouti, which has only recorded a single case.
Clusters can occur when several people experience a simultaneous exposure to the virus in their environment, for instance through contact with infected poultry or poultry feces. Or two members of a household could get infected several days apart, if the exposure is ongoing.
Investigating those types of clusters can offer clues to what puts people who are exposed to diseased birds at greatest risk of infection. Is slaughtering more or less risky than defeathering, for instance?
And if clusters begin to pop up more frequently, they could also signal that the virus has changed in ways that make it easier for it to jump to people in the first place.
"Whenever we have a group of people who are sick, especially a couple of people who are confirmed, then you always have to be wondering: Is there something different about this cluster than earlier clusters of another group of people exposed to birds?'' said Dr. Keiji Fukuda, co-ordinator of the World Health Organization's global influenza program.
"Clusters should be a constant source of new information,'' agreed infectious diseases specialist Dr. Michael Osterholm, director of the Center for Infectious Diseases Research and Policy at the University of Minnesota.
"If they are changing qualitatively or quantitatively, you may not understand why but you should constantly be looking at that.''
"Are there any clues that would give us some guide as to are we getting closer to a potential readily human-to-human transmitted agent?''
But the clusters that really set off alarm bells are those where it appears human-to-human transmission has taken place, such as was almost certainly the case last May when eight members of a family in North Sumatra fell ill in three waves.
It's generally believed a woman in the family became infected while working at a market; in the course of her illness, she infected six relatives. One, her nephew, passed the virus to his father (her brother). All but one person in this cluster died.
While Indonesian authorities insist there is no strong evidence person-to-person spread has occurred in their country, experts outside believe at least three clusters there likely included limited human-to-human spread.
Unsustained human-to-human spread is also believed to have occurred in several other countries, including Thailand, Iraq and Vietnam.
If larger clusters involving human-to-human spread started to occur, or if these groups started to involve non-family members, neighbours, or health-care workers who help care for the cases, scientists would scramble to examine the genetic makeup of the viruses involved.
"One sign that could indicate that the viruses have changed to potentially spread more easily among people would be larger size in clusters, a higher frequency of clusters, clusters among close contacts who are not necessarily blood related family members,'' Uyeki said.
"Those could be signs that the virus has acquired some newer properties. It doesn't necessarily mean a pandemic is imminent, but ... it could signal that there are changes in the virus that might cause more spread among people.''
