- "If we can't find an external source
that explains all seven confirmed cases, then we have to go with the theory
that this is human to human," says Peter Cordingley, the spokesperson
for the WHO's Western Pacific regional headquarters. Human to human transmission
within a family is believed to have occurred at least twice before, in
Thailand and Vietnam, although never involving this many people. But if
the 10-year-old boy was infected by a family member, and then went on to
infect his father, it would represent the first known time the virus had
passed from human to human to human. "It's certainly possible,"
says Gregory Hartl, a WHO spokesperson in Geneva.
-
- The above comments contain qualifiers
that keep the statements true, but misleading. The qualifiers are "at
least" for the number of cases of human-to-human (H2H) transmission,
and "known" for the number of times longer chains (H2H2H) been
reported.
-
- There has been a long list of H2H clusters.
The vast majority of familial clusters have a 5-10 day gap between the
disease onset date of the index case and other family members. In many
instances, the index case has contact with poultry, and this link is used
to discount the H5N1 in the family members. The current cluster has been
acknowledged to be H2H because the poultry source has not been identified
and the length of time between the disease onset date of the index case
(April 27) and the most recent fatality (May 15) is long and the number
of fatal cases in between is large (five plus one H5N1 confirmed survivor).
-
- However, the number of transmission is
still cloudy because WHO has failed to release the disease onset dates
for the six family members between the first and last case. The incubation
time for H5N1 is 2-4 days, which suggests the chain was H2H2H2H or H2H2H2H2H,
which is also supported by contact hisptory in the WHO update. Both of
these chains are long, but may not be the longest.
-
- Earlier this year there were two large
clusters involving several families. The first began at the end of 2005
and extended well into January. This cluster was in Turkey and confirmed
cases were identified in three families of cousins. However, the WHO updates
failed to indicate that the three family members were related and failed
to mention the hospitalizations of family members when other family members
were confirmed. Media reports suggest the index case infected his three
siblings. The index case and two siblings died and were H5N1 confirmed.
Cousins were at a family gathering, and they also developed symptoms and
10 family members were hospitalized. Two were placed in intensive care
and tested positive for H5N1. The timing of the cases suggested that these
two families represented H2H2H2H. However, these cases were followed by
the hospitalization of two more cousins who also tested positive and one
died. Thus the chain would then be extended to H2H2H2H2H. However, there
hospitalization was followed by the hospitalization of yet another set
(five) of cousins who were said to have tested negative.
-
- The reports from Turkey stopped suddenly
when the members of the fourth family were hospitalized and the number
of negative cases, including the fourth sibling of the index case, raised
credibility issues. However, WHO announced in January that they were planning
on collecting 10,000 serum samples from contacts of the cases to determine
the level of H5N1 transmission. Most patients infected with H5N1 will
develop peak serum antibodies about 3 weeks after infections. Thus, samples
should have been collected in late January and February. The results from
that testing has not been disclosed.
-
- Since the cases had connections with
poultry. These cases were not considered as H2H (or H2H2H2H2H), but there
is little reason for the cases to be focus in these three related families.
In Azerbaijan, cases extended over a month, and although wild bird feathers
may have led to infection of the index case, it is likely than transmission
to family members over such an extended time period was a long H2H chain.
-
- Thus, the current cluster in Indonesia
may not be the longest chain, but it is the deadliest, with seven fatal
cases in the eight member cluster. This may be due to a combination of
a cleavage site common in Asian H5n1 isolates, coupled with a PB2 E627K
polymorphism that is usually not found in birds and is almost always fatal
when coupled with the H5N1 cleavage site.
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