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# How to calculate the burden of SAM knowing the incidence

This question was posted the Assessment and Surveillance forum area and has 3 replies.

### kemal; J Tunne

Nutrition PM at action against hunger USA

Normal user

24 Nov 2018, 09:57

Your Question is s In the district of K2, the estimated population is 385 000 inhabitants, 21% of whom are children under 5 years old.
According to the latest SMART survey, the district has a prevalence rate GAM at 16.1% and CM (chronic malnutrition) at 21.5%.
Determine the Burden of SAM in this health district knowing that the incidence of malnutrition is 2.2. (1 pt)? I am counting on you for the calculation method of the Burden of SAM?
Here some top tips to calculate this
• Total population of the area of intervention: 385,000
• under-5 population 21%.
• chronic Malnutrition stunting 21.5%
• Estimated GAM: 16.1%;
• SAM: 2.2% (1pt)
Under-five Children = 385,000*0.21=80850 /1000 thus prevalence 3.8%=8085 SAM cases
MAM= GAM-SAM=16.1%-2.2%=25.3%

### Mark Myatt

Counsultant Epidemiologist

Frequent user

26 Nov 2018, 09:44

I think that there may be some confusion between "prevalence" and "incidence".

"Prevalence" is the proportion of the population that are cases at a given point in time. We usually know prevalence from (e.g.) SMART surveys.

"Incidence" is the number of new cases that occur over time. We almost never know incidence for SAM or MAM.

"Burden" can take a number of meanings. In the CMAM context it usually means the number of cases that will be present in a population over a period of time.

Burden is the sum of prevalent cases at the start of a period and incident cases that arise during that period. The number of prevalent cases in a population at a given point in time can be estimated using a combination of a prevalence estimate from a cross-sectional survey and population data. In the original questions we have a prevalence of 2.2% (I think) in a population of 385000 * 0.21 = 80850 children.

The number of prevalent cases is:

```    Estimated number of prevalent cases = NP
```

where N is the size of the population of interest and P is the prevalence of the condition of interest. We have N = 80850 and P = 0.022 (i.e. 2.2%):

```    Estimated number of prevalent cases = NP
= 80850 * 0.022
= 1779
```

The population burden (B) consists of both prevalent cases and new (incident) cases that are expected to occur in the program area over a given planning period:

```    Burden (B) = Estimated number of prevalent cases
+ Expected number of incident cases
```

The expected number of incident cases can be estimated as:

```    Expected numer of incident cases = NPK
```

where K is a correction factor that can be estimated in a number of ways. The most common is:

```    K = Duration of planning period
/ Average duration of a disease episode
```

A value of K = 1.6 is commonly used to give an annual burden. This gives:

```    B = NP(1 + K)
```

Using the information given in the original question we get:

```    B = 80850 * 0.022 * (1 + 1.6)
B = 4625
```

Recent work suggests that K = 1.6 may not be appropriate in all contexts. The utility of K will also depend on the timing of the prevalence survey.

Here are some links to ENN posts on this (and thr related issue of expected caseloads) matter: "3114", "2789", "2743", "1169", "157", "514".

I hope this is of some use.