It is estimated that 19 million preschool-age children, mostly from the WHO African Region and South-East Asia Region, are suffering from severe wasting (7). Childhood undernutrition is a major global health problem, contributing to childhood morbidity, mortality, impaired intellectual development, suboptimal adult work capacity, and increased risk of diseases in adulthood (7). Of the 7.6 million deaths annually among children who are under 5 years of age (1), approximately 35% are due to nutrition-related factors and 4.4% of deaths have been shown to be specifically attributable to severe wasting (7). Severe acute malnutrition remains a major cause of child mortality worldwide. While pneumonia and diarrhoea are often the final steps in the pathway, severe wasting is estimated to account for around 400 000 child deaths each year (7). For this reason, the improved management of severe acute malnutrition is an integral part of the World Health Resolution on Infant and Young Child Nutrition (WHA 63.23), to improve child survival and to reduce the global burden of disease.

In 2006, WHO released new growth standards for children aged 0–5 years (8). These represent the standards on which all WHO definitions and estimates of malnutrition, including moderate and severe acute malnutrition, and obesity are now based. In children who are 6–59 months of age, severe acute malnutrition is defined as weight-for-height less than −3 Z-score¹ of the median of the WHO growth standards, or clinical signs of bilateral oedema of nutritional origin, despite other measures being above specified cut-off values (9). Since publication of the WHO Management of severe malnutrition: a manual for physicians and other senior health workers (2), a joint statement by the World Health Organization, World Food Programme, United Nations Standing Committee on Nutrition and United Nations Children's Fund (UNICEF) in 2007 (10) acknowledged the feasibility of community health workers or volunteers identifying children affected by severe acute malnutrition, using simple coloured plastic strips that are designed to measure mid-upper arm circumference. In children who are 6–59 months of age, a mid-upper arm circumference less than 115 mm also indicates severe acute malnutrition, allowing early identification of affected children within the community before the onset of complications.

Major challenges remain to implementation of effective use of growth monitoring in primary health-care settings, to identify the most at-risk infants and children who need medical and nutritional interventions to prevent serious morbidity and mortality. The importance of this is highlighted by the strong epidemiological evidence that low weight-for-height, weight-for-length or mid-upper arm circumference are highly associated with a 5–20-fold increased risk of mortality (11). At the same time, it is necessary to examine the implications of very low anthropometry in different epidemiological settings, especially South East Asia, and to establish the equivalent anthropometric thresholds for older children and adolescents.

Malnutrition in children typically develops during the period from 6 to 18 months of age, when growth velocity and brain development are especially high. Young children are particularly susceptible to malnutrition if complementary foods are of low nutrient density and have low bioavailability of micronutrients. In addition, children's nutritional status will be further compromised if complementary foods are introduced too early or too late, or are contaminated.

The nutritional status of children can also be affected by chronic infections such as HIV. It is estimated that over 2 million children worldwide are living with HIV, 90% of them in sub-Saharan Africa (12). In a report describing children admitted to hospital in southern Africa, the prevalence of HIV in children with severe acute malnutrition was 29% and these children were more likely to die than malnourished children who were not infected with HIV (13). Higher HIV prevalence, i.e. up to 50%, has been reported among children with severe acute malnutrition (14).

Children with severe acute malnutrition have profoundly disturbed physiology and metabolism, such that if intensive refeeding is initiated before metabolic and electrolyte imbalances have been corrected, mortality rates are high. For this reason, WHO developed clinical guidance (2) on the management of the child with severe acute malnutrition. This guidance was updated in part through subsequent WHO publications on the outpatient management (10) and inpatient treatment of children with severe acute malnutrition (15, 16). Outpatient treatment of uncomplicated severe acute malnutrition is increasingly provided, using ready-to-use therapeutic foods (10). These are high-energy, fortified, ready-to-eat foods that have a nutrient content/100 kcal similar to that of F-100, the therapeutic diet used to treat children with severe acute malnutrition in hospital settings. Unlike F-100, however, ready-to-use therapeutic foods are not water based, meaning that bacteria are less likely to grow in them. These foods can therefore be used safely at home or in hospital without refrigeration and even in areas where hygiene conditions are not optimal. Ready-to-use therapeutic food can be consumed easily by children from the age of 6 months and have been shown to be effective in treating children with severe acute malnutrition in communities or in hospital after the stabilization phase. The technology to produce ready-to-use therapeutic food is simple and can be transferred to any country with minimal industrial infrastructure, while still complying with the Recommended international code of hygienic practice for foods for infants and children of the Codex Alimentarius Standard CAC/RCP 21-1979 (17).

These significant advances have not been matched by research and development in other key areas of clinical management of children with severe acute malnutrition. Furthermore, the HIV epidemic has produced a number of new research questions related to the basic science and clinical management of undernutrition in children infected with HIV. While some of the basic principles and lessons for managing children without HIV can be extended to HIV-infected children, there is little empirical evidence to guide management of this specific population.

Increasingly, severe acute malnutrition is being documented among infants who are less than 6 months of age. However, there are few data describing to what extent the pathophysiology in this population is the same as that in older children and how to approach therapeutic feeding, including the support and/or supplementation of breastfeeding. The lack of epidemiological and intervention data in young infants is common also for children who are older than 5 years. WHO has commissioned systematic reviews and convened a guideline development group to formulate guidelines for this important age group.

Lastly, the epidemiological and clinical implications of the WHO child growth standards and the populations that will be defined as having severe acute malnutrition need to be examined. While increased mortality has been reported among children with severe acute malnutrition in several African countries and Bangladesh, the burden of disease based on the revised growth standards has not been estimated, especially in India and other settings in South Asia.

Given developments in treatment options for severely malnourished children and the increasing prevalence of HIV as an adjunct to undernutrition, certain aspects of the existing guidelines on the management and treatment of severe acute malnutrition needed updating and revision. Following the review (18) of the existing recommendations (2, 9, 10), WHO identified the eight following major areas where revision of guidelines was needed:

1. Admission and discharge criteria for children who are 6–59 months of age with severe acute malnutrition

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   Admission cut-off values for the respective screening indicators

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   Discharge cut-off values for the different admission indicators

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   Admission criteria for inpatient care and outpatient care

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   Transition from inpatient care to outpatient care after stabilization

2. Where to manage children with severe acute malnutrition who have oedema

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   Which children with severe acute malnutrition who also have oedema should be managed in hospital compared to at home?

3. Use of antibiotics in the management of children with severe acute malnutrition in outpatient care

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   Do children with uncomplicated severe acute malnutrition need to be treated with antibiotics and, if so, then which antibiotic should be used?

4. Vitamin A supplementation in the treatment of children with severe acute malnutrition

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   What is the effectiveness and safety of giving high-dose vitamin A supplementation to children with severe acute malnutrition when they are receiving a WHO-recommended therapeutic diet containing vitamin A?

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   How does the timing of high-dose vitamin A supplementation (i.e. at the beginning, after stabilization or after rehabilitation) affect the effectiveness and safety of the management of children with severe acute malnutrition?

5. Therapeutic feeding approaches in the management of severe acute malnutrition in children who are 6–59 months of age

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   Does ready-to-use therapeutic food given to children with severe acute malnutrition as outpatients increase the incidence of acute diarrhoea or worsen acute diarrhoea if already present?

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   Do children with severe acute malnutrition and acute diarrhoea who are managed as outpatients require modification of therapeutic feeding approaches?

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   Does ready-to-use therapeutic food given to children with severe acute malnutrition in the rehabilitation phase, as either inpatients or outpatients, increase the prevalence of diarrhoea or worsen diarrhoea if already present, in comparison to F-100?

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   Can ready-to-use therapeutic food be given safely to children with severe acute malnutrition who have persistent diarrhoea?

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   What is the most appropriate “transition” feeding approach for changing from F-75 to F-100, or from F-75 to ready-to-use therapeutic food, for children with severe acute malnutrition who are managed in hospital?

6. Fluid management of children with severe acute malnutrition

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   What is the most effective and safest fluid-management approach for children with severe acute malnutrition diagnosed with dehydration but without shock?

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   What is the most effective and safest fluid-management approach for children with severe acute malnutrition with shock?

7. Management of HIV-infected children with severe acute malnutrition

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   What is the optimal timing for initiating and dosing of antiretroviral drug treatment?

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   What are the optimal feeding regimens for HIV-infected children with severe acute malnutrition and do these differ from those for uninfected children with severe acute malnutrition?

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   What is the value (effectiveness and safety) of vitamin A supplementation?

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   What are the most effective therapeutic strategies for managing diarrhoea?

8. Identifying and managing infants who are less than 6 months of age with severe acute malnutrition

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   What are the criteria for defining severe acute malnutrition in infants who are less than 6 months of age?

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   What are the criteria for hospital admission of infants who are less than 6 months of age with severe acute malnutrition?

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   What are the essential interventions, especially feeding approaches, for infants who are less than 6 months of age with severe acute malnutrition?

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   What are the criteria for transferring infants who are less than 6 months of age and have been treated in hospital for severe acute malnutrition to outpatient care, or discharging them from treatment?