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Field investigation of acute malnutrition cases in a village

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Lilia TUrcan

UNICEF

Normal user

1 Feb 2015, 23:31

Dear Forum, greetings from Lao.
A recent outreach in Lao uncovered increased number of SAM in three villages.
An epidemiological field based investigation would be warranted.
In Uganda, we did that though full fledged though rapid survey; yet, I wonder if there would be a methodology (description and tools) for more of a field investigation to be conducted by district health officers and healthcare workers.

Much looking forward to your suggestions
With many thanks
Lilia

Mark Myatt

Consultant Epideomiologist

Frequent user

2 Feb 2015, 17:38

Lilia,

I am not quite sure what you are asking. What would be the focus / purpose / outcome of the investigation? What question(s) do you want answered.

Sorry not to be of more help.

Mark

Mark Myatt

Consultant Epideomiologist

Frequent user

5 Feb 2015, 09:32

Lilia contacted me directly as s/he has experienced some problems posting on EN-NET:

    The ENN forum email does not seem to accept my email;
    thus, am writing on your internet-published email, to
    clarify on my earlier inquiry. 

and writes:

    The purpose of the investigation would be to document
    the event (cases of malnutrition in few village) and
    (possibly) explore potential causes. This being done
    a in manner "quicker" than a full fledged SMART survey.

    Carrying a full fledged survey is time and resource
    consuming, including, preparations. This in settings
    like Lao, of low capacity for SMART surveys is extremely
    low. Lao has a team of people carrying population-based
    survey, yet, those are statisticians + health workers
    used at periodic surveying, who cant be used ad-hoc,
    when "emergency" (outbreak) is suspected. 

    In contrast, a "field investigation" should be more of
    an "intuitive" exploration to which district officers
    here would be accustomed from older/earlier practice
    of infectious disease control supported by WHO, and
    therefore, their pool, instead of nationally-based
    or not readily available pool, could be used. 

    A field investigation could be quicker (?..though
    "dirtier?" but more accurate given we would screen
    100% of village child population). It would be 
    carried by local health officers/staff and ensure
    "ownership", local learning and empowering local staff
    to explore/analyze and propose solutions. 

    Depending on the outcome, it can evolve a full fledged
    survey but, foremost, it will offer immediate tool and
    analysis. I wondered if (aside existing protocol for,
    say MUAC screening) a light tool (questionnaire) exists,
    looking into immediate (underlying?) causes of malnutrition
    cases in village.

The first thing to note is that cross-sectional surveys (e.g. SMART) are very poor tools for investigations of this kind because the sample size of cases will usually be too small. If (e.g.) SAM prevalence is 1.5% and the sample size in n = 900 (a big sample for SMART) then there will be about 900 * 0.015 = 14 SAM cases. The large number of non-cases does contribute some power but not much. The contribution of non-cases falls away after their number reaches 4 or 5 times the number of cases. In the n = 900, p = 1.5% example, the effective number of non-cases is about 50. Cross-sectional surveys are good for estimating prevalence of disease or risk factors in a population but are not the proper tool for a "causal analysis".

The better tool to use is the case-control study. Since SAM is a rare condition we will still not have many cases to work with. We can increase power using a matched design. Matching will typically be on the "grand confounders" of age and sex. I have tended to also match on neighbourhood. For each case found we find non-cases (controls) living in the same part of the village of the same sex and similar age (e.g. +/- 3 months) of the case. It is common to take up to five controls per case. Cases and matched controls are numbered so that we know which controls are matched to which case. Data analysis is by Mantel-Haenszel stratified analysis techniques or conditional logistic regression.

Prior to starting recruitment a qualitative investigation is carried out to identify likely risk factors. In some cases you may not want to go further than this.

I have had good results with using the SQUEAC toolbox for the qualitative work and recruiting SAM cases from clinics and in the community. I have avoided using clinical controls (to avoid odd biases) and selected control from the community. This method has been taught to MoH / NGO / UNO staff and proved feasible in African settings. Local health officers (e.g. district medical officers) may already be familiar with case-control studies which are a standard tool in outbreak investigation.

Field exchange articles here and here describe experiences with the SQUEAC toolbox + matched case-control study approach.

These EN-NET and FEX links:

http://www.en-net.org/question/1383.aspx

http://www.en-net.org/question/847.aspx

http://www.ennonline.net/fex/46/causal

http://www.en-net.org/question/729.aspx

may also be useful.

I hope this helps.

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