CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 8, September 2012
AFRICA
469
Letter to the Editor
A systematic overview of prospective cohort studies of
cardiovascular disease in sub-Saharan Africa:
reply to Bovet
et al
.,
and Gao
et al
.
Dear Sir
Two groups of investigators have recently provided evidence
supporting the need for elaborated longitudinal studies to
inform successful health service and policy solutions to the
growing problem of chronic and cardiovascular disease in
sub-Saharan Africa (SSA).
1-3
In one of those studies, published
in the
Cardiovascular Journal of Africa
,
1
our group reached
such a conclusion on the basis of a systematic review of relevant
existing cohort studies conducted in SSA, published and indexed
to MEDLINE from 1966 to October 2009.
1
The feedback received from colleagues both from Africa and
beyond testifies to the interest and also the expectations of the
scientific community at large for longitudinal studies on chronic
diseases in SSA. We are particularly grateful to Drs Bovet and
Shamlaye,
4
and Drs Gao and Yuan,
5
who through two letters
published in the
Cardiovascular Journal of Africa
,
have made a
significant contribution to the debate.
Drs Bovet and Shamlaye
4
provided evidence suggesting that
our review missed some relevant studies fulfilling our entry
criteria and published in leading medical journals. They further
suggested that we omitted some SSA countries from our search.
We did acknowledge in the limitations sections of our article
that for a number of reasons, there was still a possibility that our
search did not capture all relevant studies. Therefore, we welcome
the contribution of Bovet and Shamlaye and call for an ongoing
register of African cohort studies, possibly in the columns of the
Cardiovascular Journal of Africa
along the lines of the cohort
profiles in the
International Journal of Epidemiology
.
6
However, of the eight studies listed by the two colleagues,
at least four do not fulfil the eligibility criteria of our review,
including a study from Mauritius published one year after the
completion of our review,
7
a study with a follow-up duration
shorter than six months,
8
one in which none of the predictors
of interest was assessed at baseline,
9
and one cross-sectional
study with no follow-up component.
10
It would have been more
appropriate to repeat the systematic search using our strategy, or
any other judged appropriate by the authors, and quantify the gap,
if any, between our study and what should have been optimal.
Furthermore, unlike the authors’ suggestion, we made no
restriction by country or importance of the journal of publication
in our search, nor did we claim that cohort studies have not been
conducted in Africa. Notwithstanding the above shortcomings,
the many similarities between the studies presented by the
authors and those included in our review in terms of limitations
of the data available further strengthen our conclusions. Some of
those limitations include the small sample size, the short duration
of follow up and the high rate of drop-out during follow up.
Drs Gao and Yuan also suggested that our work did not cover
all aspects of the relationship between cardiovascular disease and
related risk factors.
5
Their claim is absolutely right and would
apply to even the landmark Framingham study,
11,12
which over
the course of more than 60 years, has not yet covered all aspects
of the interaction between determinants and cardiovascular
diseases. The broadness of the cardiovascular disease field
definitely invited some prioritisation in the course of our
study. This prioritisation was based on the knowledge from the
literature of important cardiovascular diseases and their major
determinants, those cardiovascular diseases and risk factors
which are likely more important in the African setting.
From our experience researching cardiovascular diseases in
Africa, we had several strong indicators that existing relevant
cohort studies, if any, would singly not be sufficient to address
major gaps in knowledge. Therefore our aim, as stated in
our article, was to identify existing cohort studies and assess
whether these could be combined to increase the statistical power
for answering major research questions, particularly through
individual participant data meta-analyses, as done in the Asia–
Pacific region over the last decade, for instance.
13
For such a purpose, targetingmajor cardiovascular diseases and
risk factors seems in our opinion to be an appropriate approach
and would ultimately capture the studies with relevance for the
investigation of other risk factors. In the absence of individual
participant data to quantify and compare the contribution of risk
factors to disease occurrence, we are unable to understand what
sort of classification of risk factors the authors are referring to,
which incidentally, was not an aim of our study.
The time has come for the establishment of a prospective
register of African cohort studies on cardiovascular and other
chronic diseases in order to ensure the dissemination of valuable
knowledge, the identification of research needs, and the
promotion of health in the African region.
Andre Pascal Kengne,
National Collaborative Research Programme on
Cardiovascular and Metabolic Diseases, South African
Medical Research Council, Cape Town and
Department of Medicine, Groote Schuur Hospital and
University of Cape Town, Cape Town, South Africa
Bongani M Mayosi
Department of Medicine, Groote Schuur Hospital and
University of Cape Town, Cape Town, South Africa
References
1.
Kengne AP, Ntyintyane LM, Mayosi BM. A systematic overview of
prospective cohort studies of cardiovascular disease in sub-Saharan
