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Frequent Human H5N1 Transmission in Indonesia
Recombinomics Commentary 00:30
July 18, 2008

The MOH report also says that 24% of the 116 cases "occurred in 10 clusters of blood-related family members."

But the report offers no opinion on how many cases of person-to-person transmission occurred. As reported previously, person-to-person transmission was considered likely in a widely publicized cluster of eight cases (seven confirmed, one probable) in Sumatra in May 2006.

WHO reports on the Indonesian cases so far this year show only one family case cluster, involving a 38-year-old woman from West Jakarta, who fell ill in late January, and her 15-year-old daughter, who got sick in early February.

The above comments on the Indonesian Ministry of Health report include a gross underestimate of the number of cases in family clusters as well as the frequency of human to human (H2H) transmission in Indonesia.

The evidence for the underestimate can be seen in the confirmed clusters reported this year.  Most of the recent confirmed cases in Indonesia have been in family clusters, but the index case was misdiagnosed with lung inflammation, typhus, or dengue fever.  As a result, the index case was not tested for H5N1, but the infection of the relative led to bird flu symptoms and testing of a contact, leading to confirmed H5N1 cases, but not to confirmed H5N1 clusters.

These three clear clusters had the appropriate time gap between the index case and the family member which signals H2H. 

This type of cluster was clear for the first confirmed case in Indonesia in 2005.  The index case was infected from an unknown source.  She then infected her sister who died without being tested.  The father of the two girls was subsequently infected, and he tested positive (and the H5N1 isolated from him was used to make clade 2.1 vaccines, which led to Indonesia’s withholding of samples).  Eventually, the index case was confirmed because of elevated H5N1 antibodies.  All three fatalities were clearly due to H5N1, but initially only the father was a confirmed case.

The second confirmed case in Indonesia was also in 2005 and also a cluster.  In this case the index case infected her nephew.  Both cases were confirmed, but the source of the index case infection was said to be fertilizer.  However a match between putative H5N1 in the fertilizer and the index case was never demonstrated.  The nephew was tested because he was a contact, but he never developed pneumonia and quickly recovered.  Similar mild cases in Indonesia would not be tested, leading to a higher case fatality rate.

Both of these clusters clearly were H2H, but as noted above, only the Karo cluster was officially acknowledged as H2H.  Similar clusters were seen in Garut, but samples were not collected from index cases, who died before contacts were confirmed, and additional contacts, who subsequently developed symptoms, were treated with Tamiflu and were not confirmed because the treatment lowered the viral load to a level that was below detection.

Thus, it is likely that the number of H5N1 cluster members is closer to half of the confirmed cases in Indonesia, rather than the reported quarter of confirmed cases.

The timing of the news blackout that followed the three recent clusters this year was not a coincidence.

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