Journal of Urban Health: Bulletin of the New York Academy of Medicine
doi:10.1007/s11524-015-9957-0
* 2015 The New York Academy of Medicine
Tuberculosis DALY-Gap: Spatial and Quantitative
Comparison of Disease Burden Across Urban Slum
and Non-slum Census Tracts
Mariel A. Marlow, Ethel Leonor Noia Maciel,
Carolina Maia Martins Sales, Teresa Gomes,
Robert E. Snyder, Regina Paiva Daumas, and Lee W. Riley
ABSTRACT To quantitatively assess disease burden due to tuberculosis between
populations residing in and outside of urban informal settlements in Rio de Janeiro,
Brazil, we compared disability-adjusted life years (DALYs), or BDALY-gap.^ Using the
2010 Brazilian census definition of informal settlements as aglomerados subnormais
(AGSN), we allocated tuberculosis (TB) DALYs to AGSN vs non-AGSN census tracts
based on geocoded addresses of TB cases reported to the Brazilian Information System
for Notifiable Diseases in 2005 and 2010. DALYs were calculated based on the 2010
Global Burden of Disease methodology. DALY-gap was calculated as the difference
between age-adjusted DALYs/100,000 population between AGSN and non-AGSN.
Total TB DALY in Rio in 2010 was 16,731 (266 DALYs/100,000). DALYs were higher
in AGSN census tracts (306 vs 236 DALYs/100,000), yielding a DALY-gap of 70
DALYs/100,000. Attributable DALY fraction for living in an AGSN was 25.4 %.
DALY-gap was highest for males 40–59 years of age (501 DALYs/100,000) and in
census tracts with G60 % electricity (12,327 DALYs/100,000). DALY-gap comparison
revealed spatial and quantitative differences in TB burden between slum vs non-slum
census tracts that were not apparent using traditional measures of incidence and
mortality. This metric could be applied to compare TB burden or burden for other
diseases in mega-cities with large informal settlements for more targeted resource
allocation and evaluation of intervention programs.
KEYWORDS Disease burden, DALY, Disability-adjusted life years, DALY-gap, Urban
informal settlements, Slums, Tuberculosis
INTRODUCTION
More than one billion people worldwide live in urban informal settlements, defined
by the United Nations Human Settlements Program (UN-Habitat) as slums.1 This
population represents 43 % of the combined urban populations in all developing
countries.1 Residence in slums is a risk factor for a variety of adverse health
outcomes. Slum dwellers share a greater burden of such health outcomes than their
Marlow, Snyder, and Riley are with the Division of Infectious Diseases and Vaccinology, School of Public
Health, University of California, Berkeley, 530E Li Ka Shing Health Center, Berkeley, CA 94720, USA;
Maciel, Sales, and Gomes are with the Laboratory of Epidemiology, Federal University of Espírito Santo,
Vitória, Espírito Santo, Brazil; Daumas is with the Germano Sinval Faria Teaching Primary Care Center,
National School of Public Health, Oswaldo Cruz Foundation—FIOCRUZ, Rio de Janeiro, Brazil.
Correspondence: Mariel A. Marlow, Division of Infectious Diseases and Vaccinology, School of Public
Health, University of California, Berkeley, 530E Li Ka Shing Health Center, Berkeley, CA 94720, USA. (Email: mmarlow3@gmail.com)
MARLOW ET AL.
non-slum community counterparts residing in the same city.2,3 However, the
magnitude of such difference in disease burden between these communities is not
evident by routine surveillance reporting incidence or mortality. The age of onset of
a disease, as well as the duration of disability associated with that disease, cannot be
directly quantified by incidence alone. As such, there are no studies that have
quantitatively compared disease burden in urban slum vs non-slum residents within
one entire city. One measure of disease burden—disability-adjusted life years
(DALYs) reported in the 2010 Global Burden of Disease Survey (GBD-2010)—aggregated measures across regions and nations.4 The same method, however, can be
applied to compare disease burden among subpopulations within nations, such as in
urban slum vs non-slum dwellers. Slum dwellers are likely to live longer with
disability resulting from medical conditions (years lived with disability or YLD) and
more likely to suffer more years of life lost (YLL) than non-slum residents in the
same city when they develop the same disease or injuries. Such disease burden
measurements would allow quantitative evaluation of the effectiveness of intervention strategies and implementation of targeted health policies to mitigate health
disparities among different subpopulations in a nation.
As the population of urban informal settlements continues to expand in megacities of the world, targeted urban health intervention strategies become urgently
needed. In the present study, we applied the 2010 GBD metrics to compare
tuberculosis (TB) burden in urban slum vs non-slum communities in Rio de Janeiro,
Brazil. TB transmission is associated with several characteristics that define informal
settlements, including overcrowding, poor housing quality, lack of health education
and services, and inadequate implementation of TB contact tracing programs.5–8
These conditions engender other adverse health outcomes unrelated to TB. Despite
significant allocation of resources to combat TB with a rigorous national TB control
program,9 the city of Rio de Janeiro reported the second highest TB incidence rates
in the country in 2010.10 In addition, Rio de Janeiro has Brazil’s largest population
of slum dwellers, as defined by the Brazilian National 2010 Census Report.11 TB
remains a leading cause globally of DALYs among young adult males aged 15–
39 years of age,4 the largest age group in the slums of Rio de Janeiro.12 Here, we
quantitatively compared TB DALYs between formal and informal neighborhoods of
Rio de Janeiro to assess differences in the burden of this disease. We propose a new
metric called BDALY-gap^ as a way to quantitate disease burden between two
communities in the same city. Benefits and barriers to scaling up this metric for other
diseases and regions are discussed.
METHODS
Study Population and Census Tract Designation
We analyzed data from the Brazilian Information System for Notifiable Diseases
(Sistema de Informação de Agravos de Notificação—SINAN) for all confirmed,
incident tuberculosis (TB) cases reported in 2005 and 2010 that occurred in the
municipality of Rio de Janeiro. SINAN is the national notifiable disease surveillance
system of Brazil developed in the 1990s to unify and disseminate information for
improved disease monitoring and control. With respect to TB, SINAN includes
patient socio-demographic characteristics and TB infection characteristics, risk
factors, treatment, and outcome. Quality assessments of this database have been
performed routinely since its establishment, making it a recognized reliable source of
TB DALY-GAP: DISEASE BURDEN COMPARISON ACROSS SLUMS AND NON-SLUMS
disease data.9 SINAN works in three levels. First, the case is reported to the
municipality health department where the data are entered into the SINAN
database. This data are then sent to the state health department, such that cases
transferred between municipalities can be tracked and duplicates removed.
Then, the information is merged into a national database and deduplicated.
Data aggregated by municipality/state/country is published publicly online
(http://dtr2004.saude.gov.br/sinanweb/index.php). TB is a mandatory notifiable disease
in Brazil. All patients, whether they use the public or private healthcare system, need to
have their suspected diagnosis reported to the municipality health department (as part
of the Brazilian Unified Health System, Sistema Único de Saúde—SUS) in order to
receive treatment for TB. This authorization is required to receive or purchase TB
medications.
In the 2010 census survey, the Brazilian Census Bureau operationally defined
informal settlements as aglomerados subnormais (AGSN) or subnormal settlements.
According to this definition, AGSNs are census tracts with at least 51 housing units
on illegally occupied land with construction outside of existing municipal patterns or
non-secure access to essential public services.11 Many of the components of the
AGSN definition are similar to those of the UN-Habitat’s definition of slums.1
Geographic shape files and census data were obtained from open-access database of
the Brazilian Institute of Geography and Statistics (Instituto Brasileiro de Geografia
e Estatística—IBGE).13 In 2010, the IBGE defined AGSN border limits. As the 2000
census did not distinguish AGSN vs non-AGSN populations, the population
estimates from the 2010 census tracts were used for both 2005 and 2010
calculations. The population of Rio de Janeiro in 2010 was 6,299,684 inhabitants,
with 1,391,953 inhabitants living within AGSN census tracts.13
All cases were geocoded by address and mapped in ArcGIS 10 (ESRI, Redlands,
CA). Case residence was intersected with AGSN census tract limits plus a 50-m
buffer. The buffer zone was incorporated to account for two AGSN residential
address characteristics: (1) residents frequently register their address as a collective
mailbox located immediately outside AGSN limits and (2) cases that map to the
street precision level are mapped to the last available street number closest to the
AGSN limits. Therefore, cases mapped to within a 50-m radius of an AGSN census
track boundary were considered as living in the AGSN census tract. Cases that could
not be mapped to the address or street precision were excluded. Incarcerated and
homeless cases were not assigned to a census tract and hence were not included in
the analysis comparing AGSN and non-AGSN tracts.
DALY Calculation
DALYs were calculated as the sum of years of life lost (YLLs) and incident years
lived with disability (YLDs) based on the 2010 Global Burden of Disease study
methodology described elsewhere.4 Given the high quality of Brazilian TB case
reporting to the SINAN database, a prospective method or incidence approach for
calculating DALYs was employed. Consistent with the 2010 GBD methodology,
age-weighting and discounting were not applied. Incident YLDs were calculated by
TB incidence multiplied by estimated disease duration and disability weights for TB
sequelae.14 Using data from the state of Rio de Janeiro SINAN database, we
calculated disease durations by sex and HIV status for each group as weighted
averages considering total disease durations of 9, 12, and 24 months for cases that
ended in death, cure, and loss to follow-up.15 As the average duration of disease did
not differ significantly between HIV positive and negative cases nor between males
MARLOW ET AL.
and females, a standard duration of 1.1 years was applied for all incident TB cases.
We calculated YLLs by subtracting age of death from TB from the reference life
expectancy at that age.16 TB mortality was considered as Bdeath by tuberculosis^
registered in SINAN in 2010 by the health clinic responsible for the case. YLLs were
not calculated for 2005 because TB was not listed as a specific cause of death in
SINAN prior to 2007. Given this limitation, DALYs were calculated for 2010 only.
DALY-gap
DALY-gap was calculated as the difference in age-adjusted DALYs per 100,000
population attributable to cases residing in AGSN census tracts from those residing
in non-AGSN census tracts. Of 10,504 census tracts of Rio de Janeiro, 309 were
uninhabited and not included in the analysis. Census tract DALYs were stratified by
AGSN and non-AGSN and categorized by percentage of census tract residents with
access to adequate electricity, sanitation, solid waste disposal, and water services.
We also compared mean monthly income based on increments of the Brazilian
national monthly minimum wage in 2010 (US$290), average number of residents
per household, and percentage of inhabitants who rent their living space. DALY
density was calculated as DALYs per population divided by the total square
kilometer area for AGSN and non-AGSN census tracts. Data analysis was
performed in SAS 9.3 (SAS Institute. Inc., Cary, NC). DALYs per population were
mapped by census tract, with AGSN/non-AGSN census tracts designated with
different colors. Maps highlighted areas from the three major metropolitan zones of
Rio de Janeiro.
Ethical Approval
This study was approved by the Ethics Committee of the Federal University of
Espírito Santo, which has also obtained approval from the Brazilian Ministry of
Health to access the SINAN database.
RESULTS
TB incidence in Rio de Janeiro decreased from 120/100,000 person-years (7534
cases) in 2005 to 116/100,000 person-years (7276 cases) in 2010. Excluded for
census tract designation were 301 (142 in 2010) cases mapped outside of the
municipality’s limits or with unidentified addresses. Of the total cases, 755 (452 in
2010) were incarcerated and 140 (81 in 2010) were identified as homeless. In 2010,
TB incidence per population in AGSN census tracts (n=1807, 130/100,000 personyears) was higher than in non-AGSN census tracts (n=4794, 98/100,000 personyears) (Table 1).
Total DALYs/100,000 population in 2010 for all TB cases, including incarcerated
and homeless, were 265.6. DALYs resulting from HIV positive cases contributed
36.1 % of total DALYs, while those from incarcerated and homeless populations
accounted for 4.1 % of total DALYs. DALYs were higher in AGSN census tracts
than non-AGSN census tracts (306.4 vs 236.4 DALYs/100,000 pop), resulting in a
DALY-gap of 70.0 DALYs/100,000 pop (Table 1). Attributable DALY fraction for
living in an AGSN that contributed to total TB DALYs for 2010 was 25.4 %. DALYgap was highest in males 40–59 years (500.6 DALYs/100,000 pop) and in females
20–39 years (169.4 DALYs/100,000 pop) (Fig. 1). A negative DALY-gap (−149.4/
100,000) was observed only in males aged 20–39 years, with higher DALYs per
population occurring in non-AGSN census tracts for males of this age group.
YLD
Census tract
Age
Number
Non-AGSN
G20
20–39
40–59
960
Total
G20
20–39
40–59
960
Total
425
2125
1634
609
4793
235
864
565
143
1807
AGSN
DALY-Gap
n/100,000
population
35.7
138.3
122.0
72.6
97.7
47.3
172.4
192.0
141.2
129.7
32.0
YLL
YLD/100,000
population
(%)
156.2
797.5
611.9
223.4
1789.0
86.8
322.4
211.1
53.0
673.2
(8.7)
(44.6)
(34.2)
(12.5)
(100.0)
(12.9)
(47.9)
(31.4)
(7.9)
(100.0)
13.1
51.9
45.7
26.6
36.5
17.5
64.3
71.8
52.3
48.3
11.8
DALY
YLL/100,000
population
(%)
642.8
4154.7
3840.0
1170.3
9807.8
350.6
1372.1
1515.4
359.6
3597.6
(6.6)
(42.4)
(39.2)
(11.9)
(100.0)
(9.7)
(38.1)
(42.1)
(10.0)
(100.0)
53.9
270.4
286.8
139.6
199.9
70.5
273.8
515.1
355.0
258.1
58.2
DALY/100,000
population
(%)
798.6
4952.2
4452.0
1393.7
11,596.4
437.0
1694.4
1726.5
412.5
4270.4
(6.9)
(42.7)
(38.4)
(12.0)
(100.0)
(10.2)
(39.7)
(40.4)
(9.7)
(100.0)
67.0
322.3
332.5
166.2
236.4
87.9
338.1
586.8
407.3
306.4
70.0
TB DALY-GAP: DISEASE BURDEN COMPARISON ACROSS SLUMS AND NON-SLUMS
TABLE 1 Tuberculosis years lived with disability (YLDs), years of life lost (YLLs), and disability-adjusted life years (DALYs) stratified by cases residing in informal
settlement (aglomerados subnormais—AGSN) and non-AGSN census tracts of Rio de Janeiro in 2010
MARLOW ET AL.
FIG. 1 Age-specific disability-adjusted life years (DALYs)/100,000 population for male and female
tuberculosis cases in 2010. DALY-gap per 100,000 population is denoted for each age group.
Total TB YLDs/100,000 population decreased from 41.3 in 2005 to 39.1 in 2010.
During this same period, YLD-gap between AGSN and non-AGSN census tracts
experienced a minimal decrease, but increased specifically in infants less than 1 year
and in those 60 years or older (+0.1 and +1.1 YLDs/100,000, respectively). Figures 2
and 3 compare the distribution of YLDs across age groups for males and females,
respectively, in 2005 and 2010. YLD patterns remained consistent over this 5-year
period among both males and females, with the exception that the highest TB
burden in males shifted from 45 to 64 years in 2005 to 65 years and older in 2010.
FIG. 2 Age-specific years lived with disability (YLDs)/100,000 population for male tuberculosis
cases in 2005 and 2010. YLD-gap per 100,000 population is denoted for each age group.
TB DALY-GAP: DISEASE BURDEN COMPARISON ACROSS SLUMS AND NON-SLUMS
FIG. 3 Age-specific years lived with disability (YLDs)/100,000 population for female tuberculosis
cases in 2005 and 2010. YLD-gap per 100,000 population is denoted for each age group. Note: scale
is different from Fig. 2.
YLD-gap increased from 2005 to 2010 for females. Additionally, YLD-gap in male
infants nearly doubled over the time period.
Highest DALYs per population were found in AGSN census tracts with the poorest
housing and sanitation conditions, while estimates were more evenly distributed among
non-AGSN census tracts with varying rates of public service connectivity. The highest
TB burden per population was found in AGSN census tracts with G60 % electricity,
sanitation, and water accessibility (12,385.3; 12,385.3; and 467.0 DALYs/100,000
population, respectively) and G70 % solid waste disposal coverage (635.6 DALYs/
100,000 population) (Table 2). TB burden in non-AGSN census tracts was notably
higher in census tracts with mean monthly income less than the 2010 minimum wage.
Regardless of AGSN or non-AGSN census tract, the large majority of DALYs occurred
in census tracts below the average 2010 monthly household income for Rio de Janeiro
(Fig. 4). AGSN and non-AGSN combined DALY-gap between the lowest and highest
income census tracts was 323.1 DALYs/100,000 population (505.7 DALYs/100,000 for
non-AGSN census tracts only). DALY-gap by income could not be calculated for AGSN
census tracts because there was no population registered in the highest income bracket.
DALY density was over five times greater in AGSN census tracts (77.3 DALYs/
km2 for AGSN and 14.3 DALYs/km2 for non-AGSN). DALY maps which highlight
areas from three main Zones of Rio de Janeiro revealed distinct geographical DALY
patterns among census tracts (Fig. 5). AGSN census tracts represented concentrated
areas of high TB DALY burden. Non-AGSN census tracts with high TB burden
mainly bordered AGSN census tracts and uninhabited areas and were located in
low-income areas.
DISCUSSION
By calculating DALY-gap to assess TB burden in Rio de Janeiro, several key spatial
and demographic characteristics of TB burden between the slum and non-slum
MARLOW ET AL.
TABLE 2 Tuberculosis disability-adjusted life years (DALYs) by informal settlement (aglomerados subnormais—AGSN) and non-AGSN census tracts of Rio de Janeiro in 2010
Total
Census tract
characteristic
DALY
AGSN
DALY/100,000
population
Mean monthly income in $USD
G290
1222
437
290–579
6496
293
580–1448
6353
262
1449–5793
1257
96
≥5794
57
114
Average persons per household
1–2
7320
237
3–4
8062
254
5 or more
3
21
% Rented households
G10 %
3111
312
10–19 %
4359
199
20–29 %
3736
199
≥30 %
4172
343
% Households with electricity
G60 %
69
1100
60–69 %
73
788
70–79 %
178
2015
80–89 %
196
424
≥90 %
14,863
239
% Households with sanitation
G60 %
71
1080
60–69 %
71
724
70–79 %
180
1797
80–89 %
199
408
≥90 %
14,858
239
% Households with solid waste disposal
G60 %
245
598
60–69 %
145
714
70–79 %
201
663
80–89 %
308
305
≥90 %
14,480
238
% Households with water
G60 %
225
276
60–69 %
78
257
70–79 %
221
461
80–89 %
395
346
≥90 %
14,460
241
Non-AGSN
DALY
DALY/100,000
population
DALY
DALY/100,000
population
741
3255
249
0
0
367
290
378
0
–
481
3240
6104
1257
57
619
296
259
96
114
961
3282
1
381
291
12
6358
4779
1
224
233
89
1665
1019
547
1014
392
235
221
355
1447
3340
3189
3158
253
190
196
339
66
0
0
0
4180
12,385
–
–
0
301
3
73
178
196
10,683
58
788
2015
437
222
66
0
0
0
4180
12,385
0
–
24
301
5
71
180
198
10,678
88
791
1797
420
222
172
71
22
104
3877
576
847
165
311
297
72
74
179
204
10,603
659
621
1043
302
222
206
2
5
70
3962
467
23
42
259
305
19
75
217
325
10,497
51
367
592
373
223
En dash indicates categories in which there was no population
communities became evident that were not apparent by other traditional measures
of TB incidence and mortality. We applied this metric to examine TB in Rio de
Janeiro for the following reasons: (1) case reporting of TB is uniform and
comprehensive in the city, (2) the city has the second highest concentration of slum
dwellers in Brazil, (3) it reports the second highest number of TB cases in the
TB DALY-GAP: DISEASE BURDEN COMPARISON ACROSS SLUMS AND NON-SLUMS
FIG. 4 Absolute disability-adjusted life years (DALYs) per census tract by mean monthly household
income ($US) and census tract population in 2010. Purple denotes informal settlement
(aglomerados subnormais—AGSN) census tracts and orange non-AGSN census tracts. Circle size
represents absolute DALYs of census tracts. Individual graphs for AGSN and non-AGSN census tracts
were provided in the upper right-hand corner (reduced scale). Vertical and horizontal gray lines
represent mean monthly income and total population, respectively, for all Rio de Janeiro census
tracts (with and without TB cases).
country.10,11 Even though the overall TB incidence decreased between 2005 and
2010, the YLD-gap between slum and non-slum communities increased during this
time, indicating the persistent or worsening structural factors that contribute to
greater TB burden in Rio’s informal communities.
The comparison of differences in TB burden in two types of communities in the
same city by measuring DALY-gap unmasked neighborhood characteristics that
would have been missed by traditional measures of incidence. For example, in a
well-known tourist neighborhood of Copacabana, there is an AGSN census tract
community Morro do Cantagalo, which has an average monthly income of US$423
and a population of 1652 residents. This community is situated about 1.5 km from
one of the highest income census tracts of Copacabana, which has an average
monthly income of US$2189 and a population of 237 residents. Interestingly, the
high-income neighborhood actually reported a higher incidence of TB in 2010 than
Morro do Cantagalo (22 vs. 15 cases, or 9283/100,000 vs. 908/100,000 personyears). Yet, the burden of TB in Morro do Cantagalo was considerably higher (132
DALYs) than its high-income counterpart (8 DALYs). Per population, Morro do
Cantagalo suffered over double the number of DALYs/100,000 population (7990 vs.
3443), an astounding DALY-gap of 4547 DALYs/100,000. Incidence alone would
suggest TB control programs should target the high-income neighborhood over the
slum community; however, DALY-gap revealed the opposite in disease burden
between the two communities.
TB DALYs per population based on the GBD-2010 report was 142 DALYs/
100,000 for Brazil.4,13 In the present study, TB DALYs per population in Rio was
266 DALYs/100,000 population, demonstrating the higher disease burden incurred
in the urban mega-city. Furthermore, the TB DALY-gap between slum vs non-slum
MARLOW ET AL.
FIG. 5 Disability-adjusted life years (DALYs)/100,000 population by census tract in three
highlighted areas of Rio de Janeiro, Brazil in 2010. Purple denotes AGSN census tracts and
orange non-AGSN census tracts.
census tracts in Rio was 70 DALYs/100,000 population. Our findings are consistent
with a recent study in Rio de Janeiro on healthy life expectancy (HALE), another
measure of morbidity and mortality based on disability. Adults living in slum census
tracts (AGSNs) were found to have approximately half the HALE than those
residing in wealthy census tracts across all age groups.17 Taken together, the studies
provide quantitative evidence that slum residents suffer disproportionately the
weight of ill-health that occur in the same city.
Another study conducted in three slums in Nairobi, Kenya, calculated the YLLs
specific to informal settlements.18 The authors found AIDS and TB combined were
the leading contributors to YLLs in those older than 5 years, accounting for nearly
50 % of the mortality burden in these informal settlements. However, the study did
not directly compare the YLLs of these slums with those for the region or with nonslum communities. Without comparable values for formal communities, it is not
possible to determine the fraction of YLL burden attributable to living in a slum.
Much of the previous work using DALYs to identify health disparities within specific
regions has focused on ethnic disparities.19–22 However, DALY-gap in slum
communities is different from income or indigenous health gap; it addresses disease
burden of communities or neighborhoods, making it a metric easier to apply for
resource allocation. Furthermore, the spatial analysis in our study showed that the
TB burden differs greatly even across different slum and non-slum communities.
We found over one fourth of all TB DALYs in Rio could be attributed to living in
a slum. Incarcerated and homeless cases, two populations often associated with high
TB DALY-GAP: DISEASE BURDEN COMPARISON ACROSS SLUMS AND NON-SLUMS
TB infection rates, also contributed to TB disease burden (2.7 and 1.5 % of DALYs,
respectively). However, as there are no population estimates for these groups in Rio
de Janeiro, their TB burden could not be compared to other census tract
populations. Interestingly, among males aged 20–39 years, DALY/population was
higher among residents of non-AGSN (Fig. 1). DALY-gap for males of this age group
was −149 DALYs/100,000. We found that 63.1 % of DALYs (82.1 % of cases) of
the incarcerated cases with TB were in males of the same age group. The residential
addresses of the incarcerated people were not available. It is conceivable that a large
proportion of these incarcerated people may be residents of AGSNs and hence the
TB DALY in this age group may be underestimated in AGSN in our analysis.
Of particular concern is the DALY-gap in infants less than 1 year of age, especially
in male infants in which YLD-gap nearly doubled from 2005 to 2010. TB infection
in the infant population suggests ongoing transmission and can be used as an
indicator of an inadequate contact tracing program.23 While the overall TB burden
in infants decreased over time, which would indicate a successful intervention
program, DALY-gap revealed this reduction did not take place in the slum
population. This disparity suggests TB control programs in Rio may not be reaching
these at-risk populations and provides an opportunity to identify interventions that
will be effective in reducing disease burden in this population.
Highest TB burden was found in census tracts with mean monthly income lower
than the minimum wage, regardless of whether or not they were indicated as slum or
non-slum. Disease- and injury-specific studies based on the GBD-2010 data have
shown national per-capita income to be a strong predictor of mortality and DALY
loss rates.19,24 Here, the two lowest income groups contributed 94.1 % to the total
burden of TB among slum residents and 33.4 % among residents of non-slum census
tracts. Thus, low income is an important contributor for TB DALY in the slum
population, but factors other than low income are also important contributors to TB
burden among the non-slum population.
While DALYs measured across nations or regions have shortcomings, several
limitations also exist for scaling up the DALY-gap metric for other diseases and
subpopulations. Our study was made possible by the comprehensive census survey
conducted in 2010 by Brazil that divided census tracts according to a formal
definition and mapping of informal settlements as AGSN, and that TB reporting is
uniform and high in Brazil. One limitation, however, is that it is not possible to
distinctly demarcate neighborhoods into formal and informal settlements in large
cities like Rio de Janeiro. The burden of TB in non-AGSN census tracts was highest
in those tracts that bordered AGSN census tracts. These bordering zones actually
have many of the characteristics that define AGSNs. Thus, the DALY-gap we
describe here is likely to be underestimated.
The Brazilian SINAN is a well-validated surveillance system that includes TB as a
major targeted disease. Case-detection rate of SINAN reporting range was estimated to
be 88 % in 2010.9 Without these census and survey data, DALY-gap measurements
would not have been possible to calculate. While countries like India and Kenya have
made efforts to conduct census and define geographic boundaries of their urban
informal settlements,25,26 other countries with mega-cities have yet to do so. Without
definition of slum boundaries, DALY-gap will remain difficult to assess accurately.
Another limitation of comparing DALYs across subpopulations is that the same
disability weight and disease duration for incident YLDs is applied for all cases.16
Furthermore, slum populations were likely underrepresented in the most recent
survey on disability weights for GBD 2010 and concordance of disability weights
MARLOW ET AL.
across different cultures and demographics may have been overstated.27 It is very
likely that residents of slum communities experience a longer duration of disability
when they develop a disease than residents of non-slum communities who develop
the same disease.2,3 Those who develop symptoms of TB in an informal settlement
are more likely to take a longer time to seek medical care than non-slum residents
who develop TB, resulting in a more advanced disease at diagnosis. If such
individuals develop multidrug-resistant (MDR)TB, they will have a longer duration
of disability, as MDRTB will require a longer duration of treatment. As the same TB
disease duration was used to calculate YLD for all cases in the present study, DALYgaps observed here were conservative estimates. Future DALY-gap studies using
subpopulation-adapted disability weights, prevalence, and/or different slum vs nonslum disease durations will likely reveal larger differences.
DALY is already a widely used, validated methodology accessible to all governments and researchers across the globe. The expansion of DALY-gap methodology
to other regions, subpopulations, diseases, and risk factors may promote better
understanding of the burden of disease attributable to living in these underserved
communities. Temporal measures of DALY-gap will be an invaluable metric to assess
the effectiveness of slum upgrading projects, such as those being implemented in
preparation for Brazil’s major international sporting events, such as the World Cup
in 2014 and the Olympics in 2016.
ACKNOWLEDGEMENT
Funding MM was supported by NIH Research Training Grant #R25TW009338
(Global Health Equity Scholars Program) funded by the Fogarty International
Center and the Office of AIDS Research at the National Institutes of Health. ELNM,
CMMS, and TG were supported by Grant #U2RTW006885 ICOHRTA from the
Secretariat of Health Surveillance/Ministry of Health of Brazil.
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