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.