What is Severe Acute Malnutrition (SAM)?
Severe Acute Malnutrition (SAM) is a life-threatening condition defined by severe wasting, very low weight-for-height, and/or the presence of bilateral pitting edema. SAM significantly increases the risk of morbidity and mortality, particularly among children under five years of age. The condition results from a combination of poor dietary intake, underlying illnesses, and environmental factors like food insecurity and inadequate sanitation. Effective management of SAM is crucial for reducing childhood mortality and improving long-term health outcomes.
The Role of Prevalence in Public Health
Prevalence is a key epidemiological measure that quantifies the total number of cases of a condition within a population at a specific point in time. For SAM, calculating prevalence provides a snapshot of the nutritional situation in a given area, which is vital for several reasons:
- Needs Assessment: It helps health organizations understand the scale of the problem and the resources required to address it.
- Resource Allocation: Prevalence data informs decisions on where to deploy therapeutic feeding programs, allocate funding, and supply ready-to-use therapeutic foods (RUTF).
- Monitoring Trends: Repeated surveys allow health officials to monitor changes in malnutrition rates over time, evaluate the impact of interventions, and identify populations at heightened risk.
- Policy Formulation: Accurate data is the foundation for developing and refining public health policies aimed at preventing and treating malnutrition.
How to calculate SAM prevalence: The fundamental steps
The process for calculating SAM prevalence is based on data collected through representative population-based surveys, with the Standardised Monitoring and Assessment of Relief and Transitions (SMART) method being a widely accepted approach. Here is a step-by-step breakdown of the process:
- Define the Population: The calculation focuses on children aged 6 to 59 months, as this is the most vulnerable group for SAM. The target area could be a district, zone, or a specific community.
- Conduct a Standardized Survey: A survey using standardized methods, like SMART, is carried out. This involves selecting a representative sample of children from the target population using cluster sampling techniques.
- Collect Anthropometric Data: For each child in the sample, several measurements are taken:
- Weight and Height/Length: Accurate weight and length/height measurements are critical for calculating the weight-for-height z-score (WHZ).
- Mid-Upper Arm Circumference (MUAC): This measurement is taken using a specialized tape and is a rapid, effective screening tool, especially in community settings.
- Bilateral Pitting Edema: A clinical assessment for edema involves applying pressure to both feet. An indentation that persists is a sign of edematous malnutrition (Kwashiorkor) and is independently considered SAM.
- Determine SAM Cases: A child is classified as having SAM if they meet any one of the following WHO criteria:
- Weight-for-Height Z-score (WHZ) < -3 SD (below minus three standard deviations) of the WHO Child Growth Standards median.
- Mid-Upper Arm Circumference (MUAC) < 115 mm for children 6-59 months.
- Presence of bilateral pitting edema.
- Calculate the Prevalence: The prevalence is calculated by dividing the total number of children identified with SAM by the total number of children assessed in the 6–59 month age group, and then multiplying by 100 to express it as a percentage.
$Prevalence\ of\ SAM\ =\ (\frac{Number\ of\ children\ with\ SAM}{Total\ number\ of\ children\ surveyed})\times 100$
Methodologies for measuring SAM
Different indicators are used to diagnose and estimate SAM prevalence, each with its own advantages and limitations. While both MUAC and WHZ are accepted diagnostic criteria for SAM, they often do not identify the exact same group of children.
| Feature | Weight-for-Height Z-Score (WHZ) | Mid-Upper Arm Circumference (MUAC) |
|---|---|---|
| Measurement Tool | Weighing scale and stadiometer/length board | MUAC tape |
| Data Complexity | Requires accurate weight and height, plus WHO growth standards for calculation. More prone to measurement error in the field. | Simple to use and requires minimal equipment. Tapes are easy to transport and use. |
| Interpretation | Requires tables or software to convert measurements to a Z-score relative to reference populations. | A simple fixed cut-off (<115mm) is used for children 6-59 months, simplifying screening. |
| Identified Children | Tends to identify cases across a wider range of ages, including older children. | MUAC tends to identify a higher proportion of younger children with SAM. |
| Resource Needs | More time-consuming and requires standardized training for height/length measurement. | Faster and less intrusive, making it well-suited for high-volume community-level screening. |
| Case Overlap | Studies show that less than half of children identified as SAM by one method are identified by the other. | High specificity but lower sensitivity in some age groups compared to WHZ. |
Both measurements, along with the assessment for bilateral pitting edema, are critical for a comprehensive and accurate estimate of SAM prevalence. The choice and combination of indicators can have significant programmatic implications, such as the total caseload identified and resource needs.
Conclusion
Calculating SAM prevalence is a critical function of nutritional monitoring and public health programming. By using standardized methodologies like SMART surveys and combining key anthropometric and clinical criteria (WHZ, MUAC, and edema), health organizations can generate reliable data to guide their work. The use of both MUAC and WHZ as independent admission criteria is crucial, as they identify different subsets of the severely malnourished population. Accurate prevalence data is not merely a statistical figure; it represents the foundation upon which effective, lifesaving nutritional interventions are built, allowing for the strategic allocation of resources and the diligent monitoring of progress towards ending severe malnutrition.
Citations
- EN-NET. (2018). How to calculate the burden of SAM knowing the incidence.(https://www.en-net.org/forum/question/3496)
- UNICEF. (2023). National Nutrition SMART Survey Report.(https://www.unicef.org/mena/media/15741/file/National%20Nutrition%20SMART%20Survey%20Report%20.pdf)
- World Health Organization. (2023). Identification of severe acute malnutrition in children 6–59 months.(https://www.who.int/tools/elena/interventions/sam-identification)
- NCBI. (2016). Management of Severe and Moderate Acute Malnutrition.(https://www.ncbi.nlm.nih.gov/books/NBK361900/)
- BMC Pediatrics. (2020). Severe acute malnutrition and its associated factors among children aged 6 to 59 months.(https://bmcpediatr.biomedcentral.com/articles/10.1186/s12887-020-02154-1)
- NCBI. (2012). WHO Child Growth Standards and the Identification of Severe Acute Malnutrition in Children 6–60 months old.(https://www.ncbi.nlm.nih.gov/books/NBK200776/)
- FANTA Project. (2016). How to Assess Bilateral Pitting Edema.(https://www.fantaproject.org/sites/default/files/download/BPO-2.13-NACS-Users-Guide-Apr2016.pdf)
