Now that infection with OV can be readily treated with
the drug praziquantel, which is well known and readily
available to the population, the presence of eggs at a point
in time may not give much idea about past infection. For
this reason, antibody tests have been used to try to estimate
past intensity of infection in individual-based studies,
although they are not entirely satisfactory with respect to
their specificities and sensitivities when compared with the
conventional faecal examination (Haswell-Elkins et al.
1991b; Sirisinha et al. 1995). The study described in this
paper is an ecological comparison, in which inference
about the effect of OV infection on individuals is made
from an observation at group level (the groups are districts
of Khon Kaen). The inability of current faecal egg counts in
individuals to reflect their past exposure to the parasite is
one justification for this choice of study design. In addition,
for infectious diseases, ecological estimates of effect may be
more appropriate than in individual-based study designs,
which assume that the outcome in one individual is
independent of exposure and outcome in others in the same
group (Koopman & Longini 1994). The outcome of OV
infection may be better seen at group level, therefore,
where individual exposure is better captured by measures
of the intensity of infection in a population (related to a
variety of factors in the parasite’s life cycle, the environment, or in the other inhabitants) than by a single point
measurement on the individuals themselves.
Now that infection with OV can be readily treated with
the drug praziquantel, which is well known and readily
available to the population, the presence of eggs at a point
in time may not give much idea about past infection. For
this reason, antibody tests have been used to try to estimate
past intensity of infection in individual-based studies,
although they are not entirely satisfactory with respect to
their specificities and sensitivities when compared with the
conventional faecal examination (Haswell-Elkins et al.
1991b; Sirisinha et al. 1995). The study described in this
paper is an ecological comparison, in which inference
about the effect of OV infection on individuals is made
from an observation at group level (the groups are districts
of Khon Kaen). The inability of current faecal egg counts in
individuals to reflect their past exposure to the parasite is
one justification for this choice of study design. In addition,
for infectious diseases, ecological estimates of effect may be
more appropriate than in individual-based study designs,
which assume that the outcome in one individual is
independent of exposure and outcome in others in the same
group (Koopman & Longini 1994). The outcome of OV
infection may be better seen at group level, therefore,
where individual exposure is better captured by measures
of the intensity of infection in a population (related to a
variety of factors in the parasite’s life cycle, the environment, or in the other inhabitants) than by a single point
measurement on the individuals themselves.
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