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Impact of New WHO Growth Standards on the Prevalence of Acute Malnutrition and Operations of Feeding Programs --- Darfur, Sudan, 2005--2007

Acute malnutrition among children aged 6--59 months is a key indicator routinely used for describing the presence and magnitude of humanitarian emergencies. In the past, the prevalence of acute malnutrition and admissions to feeding programs has been determined using the growth reference developed by the World Health Organization (WHO), CDC, and the National Center for Health Statistics (NCHS). In 2006, WHO released new international growth standards and recommended their use in all nutrition programs. To evaluate the impact of transitioning to the new standards, CDC analyzed anthropometric data for children aged 6--59 months from Darfur, Sudan, collected during 2005--2007. This report describes the results of that analysis, which indicated that use of the new standards would have increased the prevalence of global acute malnutrition on average by 14% and would have increased the prevalence of severe acute malnutrition on average by 100%. Admissions to feeding programs would have increased by 56% for moderately malnourished children and by 260% for severely malnourished children. For programs in Darfur, this would have resulted in approximately 23,200 more children eligible for therapeutic feeding programs. For the immediate future, the prevalence of acute malnutrition in children should be reported using both the old WHO/CDC/NCHS reference and the new WHO standards. More research is needed to better ascertain the validity of the admission criteria based on the new WHO standards in predicting malnutrition-related morbidity and mortality.

Historically, measures of acute malnutrition have been based on the WHO/CDC/NCHS growth reference (1). This reference is a normalized version of the 1977 NCHS reference (2). The NCHS reference is based on data from predominantly formula-fed children collected in the United States during the 1960s and 1970s. However, at least one report has indicated a need for more internationally representative, up-to-date growth standards based on predominantly breastfed children (3). Therefore, in 2006, WHO developed new growth standards using data collected during 1997--2003 from predominantly breastfed children living in favorable conditions from sites in six regions of the world (4,5). The WHO growth standards are considered preferable because they represent how healthy children should grow, whereas the WHO/CDC/NCHS reference only represents how children grew in a specific place and time (4).

To describe acute malnutrition at the population level, two prevalence indicators are normally reported: global acute malnutrition (GAM) and severe acute malnutrition (SAM) (6). GAM and SAM are the principal indicators reported in nutrition surveys and are used to compare population prevalence of acute malnutrition across time and geographic areas. Prevalences of GAM and SAM are based on the proportion of children aged 6--59 months whose weight and height categorize them below a certain Z-score (Table 1). A Z-score is the number of standard deviations from the weight of an individual child to the reference mean weight, for a given height and sex.

To determine the need for admission to a selective feeding program, children are classified as being moderately malnourished (eligible for supplementary feeding programs) or severely malnourished (eligible for therapeutic feeding programs). In contrast to population prevalence measures (GAM and SAM), this classification has been based previously on the percentage of the median of the WHO/CDC/NCHS growth reference, as opposed to Z-scores (Table 1). Percentage median is the ratio of the weight of an individual child to the reference mean weight, for a given height and sex. The new WHO guidelines recommend that Z-scores be used not only for measures of population prevalence but also as admission criteria for feeding programs, eliminating use of the percentage median (7), because Z-scores more accurately take into account the distribution of the anthropometric measures within the population. These standards have been endorsed by other United Nations agencies and international health and nutrition bodies (e.g., the United Nations Standing Committee on Nutrition and the International Pediatric Association) and has been adopted in approximately 90 countries (7).

CDC analyzed data obtained from three annual cross-sectional nutritional surveys conducted during 2005--2007 in Darfur, Sudan, by the United Nations Children's Fund (UNICEF), the World Food Programme, and CDC. All three surveys obtained anthropometric data from children aged 6--59 months from each of Darfur's three states. Anthropometry scores for each child, including the WHO/CDC/NCHS percentage median, WHO/CDC/NCHS Z-score, and WHO Z-score, were generated.* Records with missing critical data and extreme outliers (e.g., those with Z-scores greater than ±4 from the observed mean Z-score) were excluded from analysis.

GAM, SAM, and admission eligibility for moderate and severe acute malnutrition based on the WHO/CDC/NCHS and WHO standards were defined (Table 1) (8). The prevalences of GAM and SAM were calculated for each annual survey using WHO/CDC/NCHS Z-scores versus WHO Z-scores, and compared by calculating the relative percentage change for years 2005, 2006, and 2007. To estimate the effects on admissions into feeding programs, the proportions of moderate and severe malnutrition cases were calculated for each annual survey using WHO/CDC/NCHS percentage median versus WHO Z-scores, and compared by calculating the relative percentage change for each year of data. The relative percentage change for combined data from all three years for all measures was calculated. Finally, based on projections of the percentage and numbers of children with SAM, the effects on costs for operating therapeutic feeding programs in Darfur were estimated. A full treatment course for the severely malnourished was assumed to cost $203 (95% confidence interval [CI] = $139--$274) (9).

When comparing the prevalence of GAM using WHO Z-scores versus WHO/CDC/NCHS Z-scores, an overall relative increase of 14% was observed (Table 2). For SAM, using WHO growth standards resulted in an overall relative increase of 100% compared with WHO/CDC/NCHS-based results. When comparing estimates of eligibility for feeding program enrollment for moderately malnourished children, using WHO Z-scores compared with WHO/CDC/NCHS percentage median indicated an overall relative increase of 56% (Table 3). For severely malnourished children, using WHO Z-scores showed an overall relative increase of 260% compared with WHO/CDC/NCHS percentage median.

Analysis of the 2007 data indicated that, by converting from WHO/CDC/NCHS reference to WHO standards, the projected number of severely malnourished children would increase from approximately 6,800 to 30,000. This translates to an increase in operating expenses for therapeutic feeding programs by an estimated $4.7 million (CI = $3.2--$6.3 million). This estimate does not take into account the additional cost for treating moderately malnourished children.

Reported by: O Bilukha, MD, PhD, L Talley, MPH, National Center for Environmental Health; C Howard, MD, EIS Officer, CDC.

Editorial Note:

Results of this study demonstrate that transitioning to the new WHO growth standards will have substantial effects on the population prevalence of GAM and SAM, admissions to feeding programs, and costs of program operations. This analysis shows moderate increases in GAM and substantial increases in SAM at levels similar to a previously published report based on displaced populations (10). Also, based on these estimates, three to four times as many children would be eligible for admission into therapeutic feeding programs.

The findings in this report are subject to at least one limitation. Errors might have occurred during field data collection, which can be challenging in austere settings such as Darfur, where access to the survey population often is limited because of a lack of security and a lack of qualified survey personnel.

CDC recommends that nutrition survey reports on acute malnutrition should, for the immediate future, use both the WHO/CDC/NCHS reference and the WHO standards. Considering the programmatic importance of comparing year-to-year data, if prevalences based only on the WHO growth standards were reported, they could not be compared easily with levels reported from previous years based on WHO/CDC/NCHS reference. For example, reporting a SAM level of 4.4% using the WHO standard, without explaining that it corresponds to a SAM level of 1.8% based on the WHO/CDC/NCHS reference, might be somewhat misleading. The guidelines that designate levels of GAM and SAM at which large-scale nutritional interventions are indicated should be updated to reflect expected changes in magnitude of acute malnutrition observed with the new standards. Finally, more research might be needed to determine what Z-score cutoffs are appropriate for classifying individual children as having moderate or severe acute malnutrition. The focus should be on determining cutoffs that are most sensitive and specific for malnutrition-related morbidity and mortality. If the currently recommended WHO Z-score cutoffs for admission into feeding programs are applied, both the funding and the size of the feeding programs (accounting for the number of trained staff required, infrastructure, and feeding commodities) will have to increase several-fold. If the agencies are not prepared to immediately substantially increase their feeding program funding and operations in parallel with a substantial increase in the number of children eligible for admission into feeding programs, the quality of care might be compromised and resources diluted.

WHO recommends that the new growth standards be used globally in all feeding programs for acutely malnourished children. The substantial increase in patient load expected with the adoption of the new standards underscores the need to monitor how rapidly international relief agencies and ministries of health are able to adapt in terms of enrollment rates, personnel resources, and financial expenditures.

References

  1. Dibley MJ, Goldsby JB, Staehling NW, Trowbridge FL. Development of normalized curves for the international growth reference: historical and technical considerations. Am J Clin Nutr 1987;46:736--48.
  2. Hamill PV, Drizd TA, Johnson CL, Reed RB, Roche AF, Moore WM. Physical growth: National Center for Health Statistics percentiles. Am J Clin Nutr 1979;32:607--29.
  3. World Health Organization. An evaluation of infant growth. WHO Working Group on Infant Growth. World Health Organization: Geneva, Switzerland; 1994.
  4. World Health Organization. WHO child growth standards: length/height-for-age, weight-for-age, weight-for-length, weight-for-height and body mass index-for-age: methods and development. Geneva, Switzerland: World Health Organization; 2006.
  5. de Onis M, Garza C, Onyango AW, Martorell R, eds. WHO child growth standards. Acta Paediatrica 2006;450(Suppl):1--101.
  6. World Health Organization. Physical status: the use and interpretation of anthropometry. World Health Organ Tech Report Ser 1995;854.
  7. World Health Organization and UNICEF. WHO child growth standards and the identification of severe acute malnutrition in infants and children. A joint statement by the World Health Organization and the United Nations Children's Fund. Geneva, Switzerland: World Health Organization and UNICEF; 2009.
  8. World Health Organization. The management of nutrition in major emergencies. Geneva, Switzerland: World Health Organization; 2000.
  9. Bachmann M. Cost effectiveness of community-based therapeutic care for children with severe acute malnutrition in Zambia: decision tree model. Cost Eff Resour Alloc 2009;7:2.
  10. Seal A, Kerac M. Operational implications of using 2006 World Health Organization growth standards in nutrition programmes: secondary data analysis. BMJ 2007;334:733.

* Scores generated using emergency nutrition assessment software (ENA for SMART), available at http://www.nutrisurvey.de/ena/ena.html.

TABLE 1. World Health Organization/CDC/National Center for Health Statistics (WHO/CDC/NCHS) and WHO definitions of acute malnutrition using weight-for-height and/or edema in children aged 6--59 months

Categories

WHO/CDC/NCHS

WHO

Prevalence

Global acute malnutrition

Severe acute malnutrition

Z-score* <-2 or bilateral edema

Z-score <-3 or bilateral edema

Z-score <-2 or bilateral edema

Z-score <-3 or bilateral edema

Feeding program enrollment

Moderate acute malnutrition

Severe acute malnutrition

<80% to ≥70% percentage median without edema

<70% percentage median or bilateral edema

Z-score ≥-3 and <-2

Z-score <-3 or bilateral edema

* A Z-score is the number of standard deviations from the weight of an individual child to the reference mean weight, for a given height and sex.

Percentage median is the ratio of the weight of an individual child to the reference mean weight, for a given height and sex.


TABLE 2. Prevalence of global acute malnutrition (GAM) and severe acute malnutrition (SAM) based on World Health Organization/CDC/National Center for Health Statistics (WHO/CDC/NCHS) Z-score* and WHO Z-score growth standards, by year --- Darfur, Sudan, 2005--2007

WHO/CDC/NCHS Z-score

WHO Z-score

Condition

Year

Prevalence (%)

(95% CI)

Prevalence (%)

(95% CI)

Relative change (%)

GAM

2005 (N = 1,898)

12.1

(10.3--13.8)

14.1

(12.3--16.1)

17

2006 (N = 2,171)

12.9

(11.1--14.8)

15.3

(13.4--17.2)

19

2007 (N = 2,206)

16.1

(14.8--18.2)

17.2

(15.1--19.3)

7

All years combined (N = 6,275)

13.7

(12.6--14.9)

15.6

(14.4--16.7)

14

SAM

2005 (N = 1,898)

1.5

(0.9--2.0)

3.0

(2.2--3.9)

100

2006 (N = 2,171)

1.9

(1.3--2.5)

3.1

(2.3--3.9)

63

2007 (N = 2,206)

1.8

(1.2--2.5)

4.4

(3.4--5.5)

144

All years combined (N = 6,275)

1.8

(1.4--2.1)

3.6

(3.0--4.1)

100

* A Z-score is the number of standard deviations from the weight of an individual child to the reference mean weight, for a given height and sex.

Confidence interval.


TABLE 3. Prevalence of moderate and severe acute malnutrition based on World Health Organization/CDC/National Center for Health Statistics (WHO/CDC/NCHS) percentage median* (% M) and WHO Z-score growth standards, by year --- Darfur, Sudan, 2005--2007

 

 

WHO/CDC/NCHS (% M)

WHO (Z-score)

Relative change (%)

Condition

Year

Prevalence (%)

(95% CI§)

Prevalence (%)

(95% CI)

Moderate malnutrition

2005 (N = 1,898)

6.7

(5.3--8.1)

11.2

(9.2--13.1)

67

(supplementary feeding)

2006 (N = 2,171)

7.4

(5.9--8.8)

12.2

(10.2--14.1)

65

 

2007 (N = 2,206)

8.9

(7.3--10.5)

12.7

(10.6--14.8)

43

 

All years combined (N = 6,275)

7.7

(6.9--8.5)

12.0

(11.0--13.0)

56

 

 

 

 

Severe malnutrition

2005 (N = 1,898)

1.0

(0.5--1.4)

3.0

(2.2--3.9)

200

(therapeutic feeding)

2006 (N = 2,171)

1.0

(0.5--1.3)

3.1

(2.3--3.9)

210

 

2007 (N = 2,206)

1.0

(0.5--1.4)

4.4

(3.4--5.5)

341

 

All years combined (N = 6,275)

1.0

(0.7--1.2)

3.6

(3.0--4.1)

260

* Percentage median is the ratio of the weight of an individual child to the reference mean weight, for a given height and sex.

A Z-score is the number of standard deviations from the weight of an individual child to the reference mean weight, for a given height and sex.

§ Confidence interval.

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Date last reviewed: 6/3/2009

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