Since our sampling design was cross-sectional, it is not
possible to conclude that there is a causal relationship
between H5N1 in backyard poultry in Egypt and the
variables that were significant in our statistical model.
However, our results suggest hypotheses that should be
tested more specifically in future case-control or cohort
studies. The survey respondents routinely disposed of dead
poultry or poultry feces in garbage piles either in
agricultural fields surrounding the house or the area
between neighboring houses. We hypothesize that such
outdoor disposal increases the risk of H5N1 spread
between households within a village. Backyard poultry
in the sampled villages are free-ranging. These birds are
released early each morning to forage all day in the area
surrounding the family compound. Scan sampling confirmed that free-ranging birds routinely fed on village
refuse, where they could potentially contract H5N1
through contact with dead poultry or infected feces in
the garbage, particularly as the virus can persist in dead
bird feathers for up to 160 days (Yamamoto et al., 2012). A
second hypothesis suggested by our results is that contact
between domestic geese and domestic ducks leads to
H5N1 in backyard poultry because domestic ducks are
asymptomatic carriers of H5N1 that transmit the virus to
other poultry (Songserm et al., 2006). We routinely
observed flocks of domestic ducks and geese swimming
together in irrigation canals after being released from
family compounds in the morning, providing opportunities
for interspecies transmission