"Clusters" of H5N1 infection?
What will be the 'trigger' to watch for, either in the press or on a site like ProMed, that will tell us that avian flu has gone to a probable pandemic stage?I replied:
That's really hard to say. Most likely several confirmed reports of human-to-human transmission, particularly ones where there has been a documented chain of several human hosts with no bird exposure.Over on H5N1, there's a link to an article by Helen Branswell, discussing an article which will appear in the November issue of Emerging Infectious Diseases. The manuscript contains data suggesting that several of these clusters (with possible cases of human-to-human transmission) may have already occurred.
Clustering of human cases of H5N1 avian flu infections has occurred on at least 15 occasions since late 2003 and limited human-to-human transmission of the virus may have occurred in several of these groupings, researchers will report in an upcoming issue of the scientific journal Emerging Infectious Diseases.
But key information on several of the clusters - the most recent documented in the paper occurred in early July - is still outstanding, illustrating some of the problems international health authorities will likely face if they try to put into action a plan to extinguish an emerging pandemic at source.The article also contains a comment from Michael Osterholm of CIDRAP on the clustering and pandemic potential:
"Part of the reason to highlight this is to suggest any cluster should be viewed as a worrisome event and should be thoroughly worked up so that we can ascertain if it's person-to-person (spread) or rule it out," said Sonja Olsen, acting director of the U.S. Centers for Disease Control's International Emerging Infections Program, which is based in Bangkok.
But Dr. Michael Osterholm, who is skeptical that containment of a pandemic could be achieved, said when a pandemic virus starts to spread, the clusters of cases won't look like the ones Olsen and her co-authors found.So Curtis, that might give you a better idea of what to look for--and keep an eye out for the report in EID.
"The cluster or clusters signalling this will look very different. Even in the first week to 10 days, there may be 20, 30 or more cases in a given area," said Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.
(Edited to add: the paper is out today. You can find it here).