Measuring the Burden of Severe Acute Malnutrition: Current Challenges
The inclusion of a wasting reduction indicator as one of the World Health Assembly’s global targets for maternal, infant and young child nutrition is encouraging and the publication of a Global Nutrition Report to bring the crisis of malnutrition to the attention of people around the world is welcomed. Given that one aim is to illustrate the scale and consequences of acute malnutrition, it is important to consider how severe acute malnutrition (SAM) is currently defined and measured, and whether this is comprehensive.
SAM is defined by WHO and UNICEF by a weight-for-height index (WHZ) less than -3 z-score or a mid-upper arm circumference (MUAC) less than 115 mm, or presence of oedema (World Health Organization 2009). Current estimates (2012) of 17.3 million children suffering from SAM are based on prevalence surveys counting children with a WHZ less than -3 z-score1. This figure should be taken with caution, as it does not take into account children with a low MUAC and a WHZ above -3 who are at a high risk of death. In addition, these estimates do not include children with nutritional oedema who also have a high risk of death. To fill this gap in the estimation of the SAM burden, a technical group of non-governmental organisations and academics, in partnership with WHO, UNICEF and the CMAM Forum, are currently collecting data to map the global prevalence of nutritional oedema.
Current estimates have an additional limitation, as they are obtained from prevalence data, i.e. counting all children with SAM at the time of a survey. This gives an unreliable estimate of the number of children suffering from SAM in a year, as children may become severely malnourished just after the survey took place and not be counted. Similarly, children who were severely malnourished before the survey may have recovered (or died) and thus do not appear in the statistics. To get a suitable estimate of the burden of an acute disease, a measure of incidence, i.e. of the total number of cases occurring during a year, is superior to measuring prevalence. Measuring incidence would be especially important for oedematous malnutrition, as it is a very acute condition that will be missed by most prevalence surveys. Current estimates suggest that the burden of SAM measured by incidence can be 1.6 to 8 times higher than suggested by prevalence (Garenne et al. 2009; Isanaka et al. 2011). These estimates, however are based on indirect measures of incidence, based on the calculation of average duration of SAM episodes and should be taken with caution. In the absence of more reliable incidence data, prevalence estimates continue to be used as a proxy.
There are little data on the incidence of oedematous malnutrition, although most clinicians would agree that this is an acute condition, suggesting that prevalence surveys are most unreliable to assess the burden of this form of malnutrition.
Measuring incidence of SAM implies regular screening, ideally every month, of children fulfilling the above-mentioned definition of SAM. This cannot be done, except in research settings, using the WHZ-based definition. Some community-based management of severe malnutrition programmes measure MUAC of children every month and screen for the presence of oedema. These programmes, provided they have good coverage in their screening, are in a position to provide incidence data. Analysis of the data routinely collected by these programmes should soon provide more reliable estimates of the SAM burden in areas of high prevalence.
Taking into consideration both nutritional oedema and incidence, estimates should provide a more reliable representation of the public health importance of acute malnutrition.
1 http://www.who.int/nutgrowthdb/estimates2012/en/
References:
Garenne, M., D. Willie, B. Maire, O. Fontaine, R. Eeckels, A. Briend, and J. Van Den Broeck. 2009. "Incidence and duration of severe wasting in two African populations." Public Health Nutrition, 12(11): 1974‑1982.
Isanaka, S., R.F. Grais, A. Briend, and F. Checchi. 2011. "Estimates of the duration of untreated acute malnutrition in children from Niger." American Journal of Epidemiology, 173(8): 932‑940.
World Health Organization and United Nations Children's Fund. 2009. 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. Available at: http://www.who.int/nutrition/publications/severemalnutrition/9789241598163/en/