Long-term trends in seasonality of mortality in urban Madagascar: the role of the epidemiological transition

ABSTRACT

Background: Seasonal patterns of mortality have been identified in Sub-Saharan Africa but their changes over time are not well documented.

Objective: Based on death notification data from Antananarivo, the capital city of Madagascar, this study assesses seasonal patterns of all-cause and cause-specific mortality by age groups and evaluates how these patterns changed over the period 1976–2015.

Methods: Monthly numbers of deaths by cause were obtained from death registers maintained by the Municipal Hygiene Office in charge of verifying deaths before the issuance of burial permits. Generalized Additive Mixed regression models (GAMM) were used to test for seasonality in mortality and its changes over the last four decades, controlling for long-term trends in mortality.

Results: Among children, risks of dying were the highest during the hot and rainy season, but seasonality in child mortality has significantly declined since the mid-1970s, as a result of declines in the burden of infectious diseases and nutritional deficiencies. In adults aged 60 and above, all-cause mortality rates are the highest in the dry and cold season, due to peaks in cardiovascular diseases, with little change over time. Overall, changes in the seasonality of all-cause mortality have been driven by shifts in the hierarchy of causes of death, while changes in the seasonality within broad categories of causes of death have been modest.

Conclusion: Shifts in disease patterns brought about by the epidemiological transition, rather than changes in seasonal variation in cause-specific mortality, are the main drivers of trends in the seasonality of all-cause mortality.

KEYWORDS:

• Seasonality of mortality
• changes in seasonal patterns
• epidemiological transition
• Madagascar

Responsible Editor Stig Wall, Umeå University, Sweden

Responsible Editor Stig Wall, Umeå University, Sweden

Acknowledgments

We thank Osée Ralijaona for supervising the digitalization of death records and Gilles Pison for useful comments on an earlier draft.

Disclosure statement

No potential conflict of interest was reported by the authors.

Ethics and consent

Ethical concerns regarding the free and informed consent of participants are not relevant here as the study participants are deceased persons. Ethical clearance was not sought as the dataset used for this study contains no identifiable information of any study participant.

Paper context

The seasonality of cause-specific mortality is poorly documented in sub-Saharan Africa, due to incomplete registration of deaths. Our study takes advantage of a system of death notification in Antananarivo, and shows large monthly variations in mortality among children and the elderly, with two opposite patterns in these age groups. Seasonality has decreased among children due to a reorganization of the hierarchy of causes of death. Health planning could be improved by taking into account seasonality.

Data availability statement

The dataset containing ICD-9 codes and GBD cause categories needed to replicate this analysis are available upon request.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

The project leading to this work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 690984: DEMOSTAF project.