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Methodological issues of retrospective surveys for measuring mortality of highly clustered diseases: case study of the 2014–16 Ebola outbreak in Bo District, Sierra Leone | Journal Article / Research | MSF Science Portal
Journal Article
|Research

Methodological issues of retrospective surveys for measuring mortality of highly clustered diseases: case study of the 2014–16 Ebola outbreak in Bo District, Sierra Leone

Caleo G, Lokuge K, Kardamanidis K, Greig J, Belava J, Kilbride E, Sayui Turay A, Saffa G, Kremer R, Grandesso F, Danis K, Sprecher A, Luca Di Tanna G, Baker H, Weiss HA
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Abstract
BACKGROUND
There is a lack of empirical data on design effects (DEFF) for mortality rate for highly clustered data such as with Ebola virus disease (EVD), along with a lack of documentation of methodological limitations and operational utility of mortality estimated from cluster-sampled studies when the DEFF is high.

OBJECTIVES
The objectives of this paper are to report EVD mortality rate and DEFF estimates, and discuss the methodological limitations of cluster surveys when data are highly clustered such as during an EVD outbreak.

METHODS
We analysed the outputs of two independent population-based surveys conducted at the end of the 2014-2016 EVD outbreak in Bo District, Sierra Leone, in urban and rural areas. In each area, 35 clusters of 14 households were selected with probability proportional to population size. We collected information on morbidity, mortality and changes in household composition during the recall period (May 2014 to April 2015). Rates were calculated for all-cause, all-age, under-5 and EVD-specific mortality, respectively, by areas and overall. Crude and adjusted mortality rates were estimated using Poisson regression, accounting for the surveys sample weights and the clustered design.

RESULTS
Overall 980 households and 6,522 individuals participated in both surveys. A total of 64 deaths were reported, of which 20 were attributed to EVD. The crude and EVD-specific mortality rates were 0.35/10,000 person-days (95%CI: 0.23-0.52) and 0.12/10,000 person-days (95%CI: 0.05-0.32), respectively. The DEFF for EVD mortality was 5.53, and for non-EVD mortality, it was 1.53. DEFF for EVD-specific mortality was 6.18 in the rural area and 0.58 in the urban area. DEFF for non-EVD-specific mortality was 1.87 in the rural area and 0.44 in the urban area.

CONCLUSION
Our findings demonstrate a high degree of clustering; this contributed to imprecise mortality estimates, which have limited utility when assessing the impact of disease. We provide DEFF estimates that can inform future cluster surveys and discuss design improvements to mitigate the limitations of surveys for highly clustered data.

Countries

Sierra Leone

Subject Area

Ebolaoutbreaksfilovirusdisease surveillancemortality

Languages

English
DOI
10.1080/16549716.2024.2331291
Published Date
25 Apr 2024
PubMed ID
38666727
Journal
Global Health Action
Volume | Issue | Pages
Volume 17, Issue 1, Pages 2331291
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