Commentary
How
can Epidemiology contribute to new aspirations and strategies for Public
Health? Epidemiology is a scientific discipline which has had a fundamental
role on public and global health as well as on clinical medicine. The global
aim of epidemiology is to study “The occurrence and distribution of
health-related events, states, and processes in specified populations,
including the study of the determinants influencing such processes, and the
application of this knowledge to control relevant health problems” [1]. This type of information is essential and basic
for the formulation of effective public health initiatives to improve
populations’ health, which is the target of epidemiology.
From
the late 19th century to first half
of 20th century, epidemiology had a
determinant role on the control of the infectious disease (“Infectious disease
era”), namely yellow fever, syphilis, cholera and tuberculosis. Since the
second half of the last century, epidemiology has also made important
contributions to the identification of the causes of chronic diseases, such as
cancer, cardiovascular and respiratory diseases, with focus on risk factors at
the individual level (“Risk factor era”) [2].
Although
it may seem self-evident, the identification of risk factors at the individual
level in population is not sufficient for epidemiologists to face the most
pressing public health challenges of our time, for instance the increased prevalence
of chronic diseases (e.g. obesity and diabetes), infectious diseases outbreaks
(e.g. Zika), healthy aging, HIV/AIDS
pandemic, changing environment, social inequalities, movements of and changes
in populations [2,3].
Extraordinary
advances in molecular genetics and developmental biology require to be considered
in epidemiological research, on the other hand societal contexts could not be
disregarded as well. “We need to be equally concerned with causal pathways at
the societal level and with pathogenesis and causality at the molecular level” [2]. In an era of globalization together with growing
level of diseases complexity, the reductionist approaches focusing only on
linear cause-and-effect relationships do not make sense. For this reason, it is
essential to take into account the dynamic interconnections between the
molecular, microbiologic, physiologic, anatomical, emotional, cognitive,
behavioural, social, cultural, economic and environmental
factors in understanding of both communicable and non-communicable diseases.
Epidemiologists should have a holistic vision for health and disease. But how
can epidemiology do it?
In my
opinion, and following the perspectives of some other authors, as Geoffrey Rose
(“The causes of the causes”- population perspective) [4]
and of Mervyn Susser and Ezra Susser (“Chinese Boxes”) [2],
a complex and comprehensive approach is required to be applied in
epidemiological research, combining all fields of possible interactions: from
micro-biological to macro-social aspects. This is called ecological
epidemiology.
Glass
and McAtee [5] suggested an analytic approach
with two interrelated axes: time, and levels of nested hierarchies of social
and biological organization. The time axis is based on the temporal influences
over time and could be conceptualized at the individual-level as the
life-course (from conception to death), or at the population-level in terms of
historical changes. The second axis embodied biological and social systems. The
biological hierarchy integrated genomic, molecular, cellular and multi-organ
levels. The social hierarchy nested in the following levels: micro (groups,
family, social networks, etc.); mezzo (work-sites, schools, communities,
healthcare, etc.); macro (national/state and large-area dynamics) and global
(geopolitical, economic and environmental dynamics) [5].
The multiple interactions between and within these different axes/levels induce
and constrain individual behaviours [5] and,
consequently, influence not only the determinants and outcomes of health and
disease, but also the strategies for disease prevention and health promotion.
Considering
this perspective, the role of epidemiology is to develop a sophisticated
multilevel framework on the way of thinking and doing epidemiological research,
incorporating dynamic system models, with multiple levels of causation and
taking into account the importance of gene-environment interactions and the
exposures over the life course (e.g. disease later in life could reflect early
exposures in uterus or in childhood). Thus, it is necessary to identify the causal
processes at each level and to analyse how a process at one level (e.g.
societal cohesion or cellular changes) can manifest at another level (e.g.
disease in an individual) [6]. In fact, complex
models could expedite novel hypothesis generation and early hypothesis testing, identifying key elements of complex systems to achieve
a better understanding for the disease process.
For
this reason, epidemiologic research requires a competent, well-trained and
multidisciplinary workforce, integrating epidemiologists, clinicians,
geneticists, molecular biologists, statisticians and social scientists.
Additionally, it needs to combine several types of methods: qualitative,
quantitative and mixed. Specifically, regarding the methodologies, it must be
stressed the importance of to have access to data and to invest in creation and
analysis of large databases (“Big data”), as well as of secondary data from
different populations, with demographic, genetic, medical and environmental
information (e.g. electronic health records, cohort studies, biobanks, etc.) [7]. The creation of crosscutting and
multidisciplinary research partnerships and networks, as well as the use of new
information systems, the increase of sophisticated computer software for
examining massive amounts of data and the implementation of new technologies
(e.g. biomedical technologies) will be a key role [7].
Although these could require more time, a larger team, more money and rigorous
ethical control, these may be a powerful tool for epidemiology on 21st century.
In
general, eco-epidemiology approach and its practice will allow to achieve a
more comprehensive strategy for understanding disease patterns (how diseases
are distributed in the population over time, between places and persons) and
factors that cause it [5], unravelling the
complex interplay between genetic and environmental factors and creating
effective preventive measures [7]. It does not
mean that risk-factor epidemiology should be discarded. Inversely, this
approach should be developed and applied preserving the contribution of past
eras. The key approach is to perform an appropriate use of epidemiological
research in both domains clinical and preventive medicine and public health,
considering “Levels of causation, life course trajectories, kinds of causes,
and types of diseases” [6] within a broader
framework.
In
conclusion, epidemiology is a very important tool in the detection and control
of health problems, what unquestionably have been contributed to improvement of
populations’ health over the last decades. Nowadays, epidemiology needs to be
dynamic, flexible, innovative and based on transdisciplinary
approaches. The main challenge is to do the epidemiology an “Art”. It means
that it should be applied appropriately and creatively, considering several
research designs, strategies of analysis, tools and different information
sources to answer the specific public health problems between and within
populations. With open minds, critical sense and intellectual rigor, the
epidemiologists could contribute and support the new aspirations and strategies
for Public Health, translating evidence into action, and, ultimately, reducing
inequalities in health between and within countries.
short commentary