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Child wasting and concurrent stunting in low- and middle-income countries

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Summary of research1

What we know: Cross-sectional, survey-based estimates fail to capture the dynamics of wasting, particularly the onset, recovery and persistence of wasting. Longitudinal analyses are needed to provide a richer understanding of such dynamics. 

What this research adds: A pooled analysis of 18 longitudinal cohorts among children aged 0-24 months (10,854 children and 187,215 anthropometry measurements) revealed that, overall, the prevalence of wasting was highest at birth, decreasing from birth to three months and then increasing from three to 12 months of age. In South Asia, wasting prevalence was higher at birth than at 12 months, likely driven by seasonally-influenced maternal undernutrition mediated by low birth weight (LBW). The incidence of wasting was highest in the first three months of life in South Asia, where wasting prevalence estimates may underestimate the number of children who have experienced wasting episodes seven-fold (five-fold globally). While overall the majority (87%) of children recovered from wasting, children from South Asia had lower recovery rates and a more common experience of persistent wasting. By age 24 months, half of children in South Asia experienced at least one wasting episode and 7% were persistently wasted. Concurrent wasting and stunting was also most prevalent in South Asia, with peak prevalence at ages 12-18 months. Results highlight the need to intervene early before the current 6-24 months treatment focus and for seasonally targeted maternal interventions to prevent child wasting.

An estimated 52 million children worldwide are wasted, with over half living in South Asia.2 Severe wasting can be successfully treated but relapse and mortality are high and prevalence has not decreased in 30 years.  A more complete understanding of the epidemiology of wasting is needed to develop targeted treatment and preventative interventions. Unlike the cumulative process of linear growth faltering that leads to stunting, wasting is dynamic and varies over time both within individuals and populations. Cross-sectional, survey-based estimates of wasting fail to capture this dynamic of wasting, particularly the onset, recovery and persistence of wasting.  In fact, as many as 13 times the number of children who are wasted at one point in time may experience periods of wasting within a year. Longitudinal analyses are needed to provide a richer understanding of such dynamics.

In this study, the authors conducted a pooled analysis of 18 longitudinal cohorts (10,854 children and 187,215 anthropometry measurements) from 10 low- to middle-income countries in South Asia, sub-Saharan Africa and Latin America that measured length and weight monthly among children aged 0-24 months. Cohorts ranged in size from 215 to 2,920 children. The purpose of the analysis was to estimate wasting incidence and recovery, temporal and regional variations and the concurrence of wasting and stunting. Weight-for-length z-score was used to define wasting, as it was measured in all cohorts.

Across all regions, the highest wasting prevalence was at birth, potentially linked to intrauterine growth restriction or preterm birth, with a pooled prevalence of 11.9% (95% CI: 7.0, 19.5). This is in contrast to previous global research noting that wasting prevalence peaks in children aged between 6-24 months. In South Asia, where low birthweight is common, wasting prevalence at birth was 18.9% (95% CI: 15.0, 23.7), which indicates the potential role of maternal nutrition or maternal illness as a key driver of wasting in the region.

A consistent pattern was noted in prevalence decreasing from birth to three months and then increasing until 12 months of age. However, in South Asia and Latin America wasting prevalence was higher at birth than at 12 months. Almost half (47.8%) of children who ever experienced wasting during the first two years of life, experienced the first onset in their first three months of life and an estimated 14.8% (95% CI: 9.1, 23.0) of all children experienced wasting by three months of age. These findings highlight the need to intervene early before the current 6-24 month treatment focus.  

When exploring the differences between prevalence and incidence figures, after birth a maximum of 7.0% (95% CI: 4.4, 11.0) of children were wasted (prevalence) but 33.3% (95% CI: 21.1, 48.3) of children experienced at least one episode of wasting (incidence) by age 24 months. In South Asian cohorts, the proportion was 50.5% (95% CI: 41.6, 59.3). Incidence at all ages was higher in South Asia, with the highest incidence in the first three months, even when excluding episodes of wasting at birth. Thus, wasting prevalence estimates may underestimate the number of children who have experienced wasting episodes five-fold and, in South Asia, this could be as high as seven-fold.

An exploration of seasonality revealed that average weight-for-length scores varied dramatically by calendar date in almost all cohorts, with the lowest scores noted during peak rainfall seasons. The birth month influenced the effect of the season on weight-for-length trajectories, with the risk remaining to the second year of life. In South Asian cohorts, average weight for length scores at birth varied by almost a full standard deviation depending on the month the child was born (range: -0.5 Z to -1.3 Z). This finding suggests that seasonally-influenced maternal nutrition, likely mediated through intrauterine growth restriction or preterm birth, was a major determinant of child wasting at birth.

Ultimately, the majority of children recovered from wasting (91.5% moderate wasting episodes, 82.5% severe wasting episodes).  However, compared to other regions, South Asian cohorts had lower recovery rates in the 6-18 month age period. On average, the children born wasted did not catch up to the weight-for-length of children not born wasted and children born wasted who recovered had a higher cumulative incidence of wasting after six months of age. Furthermore, there was a subset of children (3.7%) who experienced persistent wasting3. This was highest in South Asia (almost double compared to the overall estimate), with 6.9% (95% CI: 4.7, 10.2) children persistently wasted over the first two years of life.

Concurrent wasting and stunting was most common in South Asia. Fourteen per cent of children were both wasted and stunted during at least one measurement and children ever wasted in the first six months were 1.8 (95% CI: 1.5, 2.3) times more likely to be both wasted and stunted between ages 18-24 months with peak prevalence at ages 12-18 months.

Among anthropometry measurements of wasted children, a large proportion was also classified as underweight (37.9%) or stunted and underweight (39.9%); the highest proportion of only-wasted children occurred at birth (6.2% of all children).

Limitations of the analysis include a lower length-for-age z score in South Asian cohorts (that may lead to overestimates in wasting recovery), inconsistency in the treatment referral data and the age of follow up between cohorts, wasting based on weight-for-height only (MUAC is associated with risk) and no adjustment for gestational age for birth anthropometry.

The authors conclude that these results offer important insights for wasting interventions and, in particular, preventative actions. Seasonally targeted interventions to prevent wasting in food-insecure populations could offer an important solution, particularly in South Asia where at birth variations were noted. Seasonal maternal nutrition interventions could be considered within this region. Extending the current focus of interventions to the 0-6 months old age group could also be essential; however, preventative and therapeutic intervention in this age group must be integrated with current infant and young child feeding practices and recommendations for exclusive breastfeeding. 

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Endnotes

1 Mertens, A., et al. (2020). Child wasting and concurrent stunting in low- and middle-income countries medRxiv: 2020.2006.2009.20126979. www.medrxiv.org/content/10.1101/2020.06.09.20126979v1

2 Based on old estimates, from World Health Organization Joint child malnutrition estimates – Levels and trends (2019 edition). www.who.int/nutgrowthdb/estimates2018/en/ (2019). More recent estimates are available in the 2020 edition (144 million children globally are stunted).

3 Persistent wasting was defined as ≥50% of weight-for-length measurements from birth to 24 months falling below -2.

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Child wasting and concurrent stunting in low- and middle-income countries. Field Exchange 63, October 2020. p88. www.ennonline.net/fex/63/concurrentwastingstunting

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