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H5N1 Transmission in Clusters Is Not Limited to Blood Relatives
May 29, 2006
So far, scientists think, all such case have involved passing the virus between blood relatives. Some experts theorize that may mean some people have a genetic susceptibility to the disease, but there is no evidence to support that.
The above comments, indicating that all H5N1 bird flu transmissions in clustwers are between blood relatives, are false. There are several examples of H5N1 confirmation in cluster members that are not blood relatives. In 2005 the largest familial cluster was in a family of five in Haiphong. All five family members were hospitalized on the same day and all were H5N1 confirmed. The family consisted of a mother, father, and three daughters, so transmission was not limited to blood relatives.
Similarly, in 2005 there was a cluster involving a pair of siblings and the nurse of the index case. The nurse was not a blood relative and had no exposure to poultry.
More recently there was a large cluster in Azerbaijain involving siblings and a close friend who was also not a blood relative.
Since most family members are blood relatives, most infected in familial clusters will be blood relatives, but these are the people who are in close contact with infected family members. The close contact is a major driver of these infections, which are largely limited to family members.
In the Azerbaijan cluster, all confirmed cases were siblings. There was no reported transmission to either parent. Similarly the large cluster of confirmed cases in Turkey also involved siblings. There was no confirmed transmission to either parent. Thus, even though both parents were blood relatives to the siblings, none were confirmed to have been infected.
Although most family members are blood relatives and all members of the Sumatra cluster were blood relatives, the exceptions cited above weaken evidence to support a genetic susceptibility as a major driver of familial clusters.