Since the advent of Covid-19 into human society, the terms epidemiology and public health have resonated widely across media and become familiar but not uniformly well understood. I was recently asked, at a webinar for science students, if these are distinct or interconnected disciplines. This question calls for clarity on definitions and applications.
Epidemiology is an academic discipline linked to knowledge-generating research on the dimensions, distribution and determinants of disease in a population. It derives from the Greek words ‘epi’ (upon) and ‘deimos’ (people). The definition was later extended to include disease prevention through actions at the population level. It is restrictive to consider only disease as the subject of epidemiological research. What about health, the converse of disease? It has positive determinants worthy of study. Why are some populations healthier than others? So, in modern epidemiology, one studies the dimensions, distribution and determinants of both health and disease, coupled with a search for evidence on what works well for disease prevention and health promotion.
Epidemiology uses several research designs to answer questions. Cross-sectional surveys usually measure the variable of interest in a random sample of the population. Antibody surveys of Covid-19, recently conducted in different parts of India, are an example. As are surveys for prevalence of diabetes or hypertension. Case-control studies compare people who developed a disease or health outcome with those who didn’t, to ascertain differential exposure to any suspected cause. What proportion of persons who developed mouth cancer were tobacco chewers compared to those who were cancer-free? A cohort study follows people over a long period to see if a particular baseline exposure leads to an adverse outcome in the future.
This is useful to study the association of dietary elements or patterns with outcomes such as heart disease or cancer. Randomised clinical trials compare people, differentially assigned to intervention and control groups, to assess impact. Vaccine or dietary intervention trials are examples. While randomised trials are considered to be least burdened by methodological weakness, all research designs have some advantages and are used as appropriate. Qualitative research methods are useful in elucidating behavioural components and aid both in framing the right research questions and explaining the observations.
Public health extends the knowledge gleaned from epidemiology and other forms of health research into various measures to improve health. It does so through transformational policies, systems, programmes and community engagement. Whether it is pollution control and sanitation or tobacco taxation and legislation to mandate seat belts and helmets, policy instruments have a great impact on population health. System efficiencies in provision of health services, from child immunisation to emergency medical transport, are addressed by public health.
Workforce planning and optimisation of expenditures are also health system issues. Access to services, drugs and technologies as well as affordability of care are integral to public health. It also conducts health impact assessment of policies and programmes in other sectors that impact on health, to make them more sensitive and responsive to public health goals. Programme design, implementation, monitoring and evaluation are also important functions of public health. Energetic community engagement and effective behaviour change communication are critical for public health success. Wearing masks and physical distancing in these times or avoiding smoking and spitting in public places are examples.
Removing stigma through active community leadership is a proactive endeavour. In engaging with communities, public health also interfaces with health rights and other human rights. Epidemiology informs public health, through rigorous research, supported by the strength of statistics. It helps set priorities for public health actions and assess their impact. While epidemiology is central to prioritisation and planning in public health, the multi-sectoral nature of public health interventions calls for multi-disciplinary learning that extends beyond epidemiology.
The knowledge platform of public health invites a confluence of life sciences (inclusive of human and animal biology, environmental sciences and ecology), social and behavioural sciences, anthropology, epidemiology, biostatistics, demography, health economics, political science and public policy, communication sciences, public health engineering and health technologies, public health law and human rights. The pathway of public health connects knowledge to action and further to impact and equity.
Ideally, such broad interdisciplinary learning platforms should exist in universities. Indian universities are only recently beginning to recognise this role. Medical colleges too have long ignored the need for multi-disciplinary public health education. Such education, wherever provided, must not only be broad-based but also strongly health-policy oriented. While it must be academically strong, it is also a field of practice. At both national and state levels, public health cadre must be created to bring the vigour of public health expertise into the system and to conduct health impact assessments of policies in other sectors. Since it is multi-disciplinary in learning and multi-sectoral in implementation, every Indian can contribute to advancing public health through actions in any field that impacts health. Public health is indeed the broadest bridge between science and society.
Dr K Srinath Reddy
President, Public Health Foundation of India. Views are personal