Social determinants of the changing tuberculosis prevalence in Việt Nam: Analysis of population-level cross-sectional studies

Background An ecological relationship between economic development and reduction in tuberculosis prevalence has been observed. Between 2007 and 2017, Việt Nam experienced rapid economic development with equitable distribution of resources and a 37% reduction in tuberculosis prevalence. Analysing consecutive prevalence surveys, we examined how the reduction in tuberculosis (and subclinical tuberculosis) prevalence was concentrated between socioeconomic groups. Methods and findings We combined data from 2 nationally representative Việt Nam tuberculosis prevalence surveys with provincial-level measures of poverty. Data from 94,156 (2007) and 61,763 (2017) individuals were included. Of people with microbiologically confirmed tuberculosis, 21.6% (47/218) in 2007 and 29.0% (36/124) in 2017 had subclinical disease. We constructed an asset index using principal component analysis of consumption data. An illness concentration index was estimated to measure socioeconomic position inequality in tuberculosis prevalence. The illness concentration index changed from −0.10 (95% CI −0.08, −0.16; p = 0.003) in 2007 to 0.07 (95% CI 0.06, 0.18; p = 0.158) in 2017, indicating that tuberculosis was concentrated among the poorest households in 2007, with a shift towards more equal distribution between rich and poor households in 2017. This finding was similar for subclinical tuberculosis. We fitted multilevel models to investigate relationships between change in tuberculosis prevalence, individual risks, household socioeconomic position, and neighbourhood poverty. Controlling for provincial poverty level reduced the difference in prevalence, suggesting that changes in neighbourhood poverty contribute to the explanation of change in tuberculosis prevalence. A limitation of our study is that while tuberculosis prevalence surveys are valuable for understanding socioeconomic differences in tuberculosis prevalence in countries, given that tuberculosis is a relatively rare disease in the population studied, there is limited power to explore socioeconomic drivers. However, combining repeated cross-sectional surveys with provincial deprivation estimates during a period of remarkable economic growth provides valuable insights into the dynamics of the relationship between tuberculosis and economic development in Việt Nam. Conclusions We found that with equitable economic growth and a reduction in tuberculosis burden, tuberculosis became less concentrated among the poor in Việt Nam.

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Unfunded studies
Enter: The author(s) received no specific funding for this work.  1 2 Evidence before this study 3 Historically, large reductions in tuberculosis prevalence globally have been ascribed to changes in living 4 standards, such as housing and nutrition, that come with economic development. Previous studies have 5 shown that social protection policies (a component of economic development) may reduce tuberculosis 6 incidence, but that these gains are dependent on amount invested in social protection policies. However, 7 direct evidence of the interaction between economic growth and TB burden is limited and missing with 8 regard to equity.

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Added value of this study 11 We used data from consecutive TB prevalence surveys conducted during a time of rapid economic 12 growth in Viet Nam to analyse the associations between equitable economic development and 13 reductions in TB prevalence. We found a significant shift in the distribution of TB from 14 disproportionately affecting the poor towards a more equitable distribution of the reduced TB 15 prevalence among the population, closely linked to neighbourhood poverty indicators.

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Our work contributes to the body of evidence of social determinants of TB prevalence. Furthermore, The relationship between bacteriologically confirmed tuberculosis disease (TB) and poor socio-

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and support for the poor and the sick. They found that social protection may reduce the incidence of TB 15 by 76% (2). In evaluating the relationship between social protection and economic development, Siroka 16 et al. found that tuberculosis prevalence is reduced with increased spending on social protection though 17 this effect plateaued when spending more than 11% of gross domestic product (GDP) on social 18 protection (5). Although these studies provide evidence that economic growth and social protection are 19 associated with reductions in TB burden, they did not explore how the distribution of TB prevalence 20 changes during economic growth.

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Viet Nam is an example of a country that has experienced notable sustained economic growth. National 23 TB prevalence surveys were conducted in Viet Nam in 2007 and 2017 (9,10). When differences in TB 24 screening and diagnostic practices were accounted for, a comparative study showed a decline in TB 25 prevalence over the ten-year period (11). The study found a 37% reduction in the prevalence of culture-26 positive TB, a 53% reduction in the prevalence of smear-positive TB, and no significant reduction in 27 smear-negative -or subclinical TB. The change in TB prevalence was more pronounced among men, 28 people living in rural areas, as well as in provinces in the North and South of the country (11).

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In 1986 a series of economic reforms, the Dổi Mới Policy, were introduced which included investments 31 in health and education (12). Since then, Viet Nam has experienced rapid and sustained economic       of clay floors, wood as fuel for cooking, ownership of a stereo system, television, motorbike, or car.

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From the 2017 survey, the presence of a fridge, computer, air conditioner, washing machine and water 6 heater was also included in the survey. We restricted the asset indices to the same six consumption 7 categories in 2007 and 2017 (24). Using the index, households were divided into groups of their relative 8 wealth and differences in disease prevalence compared between these groups. We assigned 9 consumption data responses as provided by the self-declared head of the household to all members of

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The relationships between TB prevalence, subclinical TB prevalence and SEP are not only explained 21 by individual level risks, but also by interactions between hierarchical levels including the household 22 and wider neighbourhood. In our analyses, we investigated the association between the change in TB 23 prevalence, relative household SEP and absolute provincial poverty (28). We used log-binomial models 24 to examine dependencies between variables nested in each group. We used multilevel models (MLM) 25 with group-and individual-level intercepts as random effects. MLMs aim to explain the association 26 between tuberculosis prevalence over time while taking into account that poverty and the risk of 27 contracting tuberculosis is clustered geographically and in households. MLMs allow us to analyse how 28 the neighbourhood effects explain variation in change in TB prevalence over time.

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By partially pooling varying coefficients, we quantified the relationship between variables where we 31 expected the coefficients to vary between neighbourhoods. The Hausman test was used to test the 32 correlation between random error and individual effects (regressors) in the model (see S1 Text).

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The characteristics of study participants are summarised in Table 1     Where SD is the standard deviation, a measure of dispersion of the mean.   and Confidence Intervals (CIs) are estimated using log-binomial mixed effects statistical models. Coefficients are weighted for stratification (differential cluster size, participation by age and sex, stratification by areas and post stratification weight). AIC refers to the Akaike Information Criterion a measure of model fit with a lower value indicating a better-fit model.

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In Table 2     We found that in the context of rapid economic growth and equitable distribution of resources in Viet 3 Nam, there was a shift in the distribution of TB from being concentrated among the poor to a more 4 equal distribution among households of different SEP. In the 2007 survey, older age, being male and 5 living in an urban centre was associated with TB prevalence. In the 2017 survey, the association 6 between older age and TB prevalence reduced with urban living. Multi-level models showed the 7 importance of neighbourhood poverty in explaining some of the change in TB prevalence observed.

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Studies investigating the association between reductions in TB incidence and economic development 10 have been conducted in a range of settings (1)(2)(3)5,7,29). Relationships between economic development 11 and TB prevalence are challenging to examine given distal relationships that influence the causal 12 pathway. Economic development may be measured as an increase in country GDP which represents 13 market productivity, but this is only one aspect of economic development. If economic development 14 increases wealth inequality in a population, patients' vulnerability to TB disease may increase (7). The   However, this is mediated by lower participation in the second survey of wealthy households because 1 of the expansion of the Vietnamese National Health Insurance, making free health check-ups for 2 participation in a TB prevalence survey less attractive (1,3). Despite lower participation from relatively 3 wealthier households, we found that TB burden was more concentrated among the wealthy in the 2017 4 survey than in 2007 suggesting selective participation.

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We found that the relative household SEP was weakly associated with TB prevalence after controlling    the district is situated with Viet Nam as well as the percentage of people in the district who are 21 considered poor (the district poverty rate). We also estimated the absolute wealth of households and the 22 primary results of the study held across the different measurements used. While TB prevalence surveys 23 are valuable for understanding socio-economic differences in TB prevalence in countries, given that 24 TB is a relatively rare disease in the population studied, there is limited power to explore the socio-25 economic drivers of tuberculosis prevalence (6). However, combining repeated cross-sectional surveys 26 with neighbourhood deprivation estimates during a period of remarkable economic growth provides 27 valuable insights into the dynamics of the relationships between TB and economic development in Viet 28 Nam.

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This is the first study to use repeat direct measurements of TB burden to empirically examine the 33 relationship between equitable economic development and a reduction in TB prevalence. We found that 34 with equitable economic growth and a reduction in TB burden, TB became less concentrated among 35 the poor in Viet Nam.

Figure
Click here to access/download; Figure;figures.pdf   . Illness concentration curves. The straight line (red dash) represents the equal distribution line, while the blue curve is the cumulative TB prevalence in the population ranked by assets. The blue shaded area is the uncertainty interval. A curve above the equal distribution line means that TB is concentrated among the poor and a curve below the equal distribution line means that TB is concentrated among the wealthy. Concentration curves for TB associated symptoms are included in S1 Text.