Biology Reference
In-Depth Information
TABLE 13.3 Disabling sequelae and disability weights for ascariasis included in the
1990 GBD study and 2010 study, stratified by intensity of infection
Study/intensity of infection Sequelae and case definition
Disability weight
1990 STUDY
Lower worm burden
threshold
Contemporaneous cognitive deficit:
reduction in cognitive ability in children
aged 5
0.006
14 years, which occurs only
while infection persists
e
Lower worm burden
threshold
Cognitive impairment: delayed
psychomotor development and impaired
performance on language, motor skills,
equivalent to 5
0.024
10 point deficit in IQ
e
Higher worm burden
threshold
Intestinal obstruction: blockage of the
intestines due to worm mass
0.463
2010 STUDY
Light intensity infection
None
Medium intensity
infection
Mild abdominopelvic problems,
including obstruction of the terminal
ileum by a bolus of worms, which is
common in children under 10 years
0.0108128
High intensity infection
Mild infectious disease, acute episode
0.0296199
Wasting, underweight and marasmus
0.1244958
records or institutional data). In order to represent the geographical
variation in prevalence within countries, they assumed that infection
prevalences between communities in the same country were normally
distributed and that the standard deviations of these normal distributions
increase linearly with the mean prevalence. However, analysis of data
available in the Global Atlas of Helminth Infection suggests that while
standard deviations increase with prevalence, within-country distribu-
tions are more skewed than assumed and a logit-normal distribution, in
fact, provides a better fit of the data (Pullan and Brooker, unpublished).
Finally, prevalence estimates were calculated for four age groups,
weighted according to the well-established age pattern of A. lumbricoides
infection
3
e
4
: an age weight of 0.75 for 0
e
4 years, 1.2 for 5
e
14 years, and 1
for 15 and above years.
For the 2010 GBD study, prevalence estimates were provided
by the intestinal nematodes expert group (Pullan and Brooker, unpub-
lished)
see above and
Table 13.2
. Estimates were provided separately
for the years 1990, 2005, and 2010, with age-adjusted estimates calculated
using the same age weights as used by Chan et al.
e
