Factors Influencing Disease Patterns: Communicable vs. Non-Communicable

Why does one neighbourhood battle dengue every monsoon while another struggles with rising rates of diabetes and heart disease? The answer lies in a complex web of factors that shape who gets sick, when, and why. Diseases rarely appear out of nowhere. They emerge from the interplay of biology, environment, behaviour, and the social conditions we live in. Understanding these determinants is the first step toward predicting outbreaks, designing interventions, and explaining the dramatic shift India is currently witnessing from communicable to non-communicable diseases (NCDs).

What do we mean by “determinants” of disease? 🔗

A determinant is any factor, biological, behavioural, social, economic, or environmental, that influences the occurrence, severity, or distribution of a disease. Epidemiologists often classify these into proximate (or proximal) determinants, which act directly on the body, and distal determinants, which work indirectly through social and structural channels. The Centers for Disease Control and Prevention defines a risk factor as an aspect of personal behaviour, environmental exposure, or hereditary characteristic associated with an increased likelihood of disease or injury. Both communicable diseases (CDs) like tuberculosis, malaria, and diarrhoeal infections, and non-communicable diseases (NCDs) like diabetes, hypertension, and cancer, are shaped by these layers, just in different proportions.

Proximate determinants: the direct drivers 🔗

Proximate determinants are the most immediate causes of disease. They are the factors that biologically or behaviourally translate into illness. For population health scientists, three categories stand out: maternal factors, environmental contamination, and personal health practices.

Maternal factors 🔗

A person’s risk of disease often begins before birth. Maternal age, nutritional status during pregnancy, anaemia, gestational diabetes, and exposure to infections all shape the long-term health of the child. Low birth weight, for instance, is linked not only to higher infant mortality but also to a greater risk of developing hypertension and type 2 diabetes in adulthood, a phenomenon known as the Developmental Origins of Health and Disease (DOHaD) hypothesis. A Lancet Global Health analysis highlighted that individual-level factors specific to each pregnant woman, such as age, genetics, pre-existing health conditions, and exposure to physical, chemical, and biological hazards, drive much of the maternal health risk profile. In India, where roughly half of pregnant women are anaemic, the cascading impact on both communicable infections in infancy and NCDs in adulthood is substantial.

Environmental contamination 🔗

The physical environment is one of the most powerful proximate determinants. Contaminated drinking water, poor sanitation, indoor air pollution from biomass cooking fuels, and outdoor air pollution from vehicles and industry create the conditions for both infectious and chronic diseases. A research analysis of National Sample Survey Office data found that income, sex, and the availability of safe drinking water are key determinants of the presence of diseases in India. Waterborne pathogens cause cholera, typhoid, and diarrhoeal illness, while fine particulate matter (PM2.5) is now firmly linked to cardiovascular disease, stroke, and chronic respiratory illness. Environmental scientists categorise pathogens by their transmission system, noting that the impact of proximal environmental characteristics on disease burden is mediated through transmission cycle dynamics, person-to-person spread, vector-borne routes, or water-and-food contamination.

Personal health practices 🔗

Behaviour matters enormously. Hand-washing, breastfeeding, vaccination uptake, food safety, mosquito-net use, sexual practices, tobacco and alcohol consumption, diet, and physical activity together form the personal health practice category. For communicable diseases, hygiene and immunisation are decisive. For NCDs, the picture shifts to tobacco, alcohol, diet, and inactivity, the so-called “big four” lifestyle risks. According to public health reviews, unhealthy diet, tobacco, alcohol, and a sedentary lifestyle are well-established determinants of NCDs, and social isolation has emerged as a risk factor for coronary heart disease and stroke. The WHO estimates that sedentary lifestyles now affect over 31% of Indian adults and 80% of adolescents, with food shifting toward processed, calorie-rich items high in fats, sugars, and salt.

Socio-economic factors: the underlying scaffolding 🔗

Beneath the proximate causes lies a deeper layer, the social and economic conditions in which people are born, live, and work. The World Health Organization’s Commission on Social Determinants of Health argued that this scaffolding ultimately decides who is exposed to which proximate risks and who can avoid them. Socio-economic determinants operate at three nested levels: individual, household, and community.

Individual-level factors 🔗

At the individual level, education, occupation, income, gender, and caste shape both exposure and access to care. Better-educated individuals are more likely to seek timely treatment, adopt preventive behaviours, and understand health information. A study using the Longitudinal Ageing Study in India (LASI) found that the prevalence of communicable diseases was significantly higher among uneducated elderly compared to those with higher education. Gender intersects with this strongly: women in India often face delayed diagnosis for both infectious and non-communicable conditions because of unequal decision-making power within households and lower autonomy in seeking healthcare.

Household-level factors 🔗

The household is the primary unit where health risks accumulate. Crowded living, poor ventilation, lack of toilets, food insecurity, and use of solid fuels for cooking dramatically increase the risk of tuberculosis, respiratory infections, and diarrhoeal disease. At the same time, household consumption patterns, the type of cooking oil, the proportion of processed snacks, the availability of fruits and vegetables, drive the family’s collective NCD risk profile. Household wealth also determines whether out-of-pocket expenditure on a sudden illness pushes the family into poverty, a phenomenon that affects millions of Indians each year.

Community-level factors 🔗

Beyond the household, the community sets the stage. The presence of functional health centres, immunisation outreach, water and sanitation infrastructure, road quality, recreational spaces, and even social cohesion all matter. State-level variations in India illustrate this powerfully. Research shows that India faces a sharply increasing prevalence of type II diabetes among municipal populations (5-15%), among semi-municipal populations (4-6%), and among countryside populations (2-5%), along with the highest tuberculosis incidence in the world at around 2.0 million cases each year. The same studies note that the burden of communicable diseases is concentrated in less-developed states like Bihar, Odisha, Assam, and Uttar Pradesh, while NCDs dominate in Kerala, Maharashtra, and Tamil Nadu, a textbook example of how community-level development reshapes disease patterns.

Technological and medical advancements: a double-edged sword 🔗

Few forces have reshaped disease patterns as dramatically as technology and medicine. Vaccines, antibiotics, oral rehydration therapy, improved diagnostics, and modern surgery have collectively saved hundreds of millions of lives. Smallpox has been eradicated; polio is nearly gone; child mortality from diarrhoea and pneumonia has plummeted. India’s national disease burden study confirms that the contribution of NCDs to total disease burden in Disability-Adjusted Life Years rose from 30% in 1990 to 55% in 2016, with deaths from NCDs rising from 37% to 61% in the same period, a clear sign that medical progress has pushed back communicable diseases.

But the same technological revolution that conquered infections has also reshaped the way we live, and not always for the better. Mechanised work, motorised transport, screens, processed foods, urban concrete jungles with little space to walk, and longer life expectancy have all combined to fuel an epidemic of chronic disease. As one analysis describes it, the epidemiological transition is driven by the availability of new treatments, economic development, and demographic changes, but social determinants of health such as income, housing, and education ultimately shape who dies of what.

The Indian transition in numbers 🔗

India is now firmly in the middle of this epidemiological shift. A government and academic review notes that NCDs such as cardiovascular diseases, diabetes, cancer, and chronic respiratory ailments now account for nearly 63-65% of all deaths in India, up from about 37.9% in 1990. Roughly one in four Indians is at risk of dying from an NCD before the age of 70. The financial burden is equally striking: NCDs are projected to cost the Indian economy several lakh crore rupees annually by 2030. Tobacco use affects nearly 28% of adults, and air pollution, both household and ambient, has become a top-tier risk factor, prompting India to set an unprecedented tenth NCD target focused specifically on household air pollution.

The double burden 🔗

India is not simply replacing one disease type with another, it is shouldering both at once. Tuberculosis, malaria, dengue, and diarrhoeal disease have not disappeared; they coexist with diabetes, hypertension, and heart disease, often within the same household or even the same patient. Researchers describe this as the double burden of disease, and it makes health planning especially challenging. The same hospital ward may treat a malnourished child with severe pneumonia and an elderly patient with stroke complications, requiring vastly different resources, training, and policy responses.

Bringing the determinants together 🔗

The most useful way to think about disease determinants is as a layered system. At the innermost layer sit the proximate causes, the microbes, the behaviours, the maternal and environmental exposures that act directly on the body. Surrounding them are socio-economic factors at individual, household, and community levels that decide who is exposed and who can protect themselves. Wrapped around all of this is the broader force of technological and medical change, which can both protect against disease and inadvertently create new risks. Tackling India’s dual disease burden therefore requires action on all three layers at once: cleaner water and air, stronger primary care, healthier diets, education for women, urban design that encourages walking, and policies that regulate tobacco, alcohol, and ultra-processed food.

What do you think? If you had to design a single public health intervention for your home state, would you target a proximate determinant like sanitation or tobacco use, or a distal one like education or urban planning, and why? And as India continues its epidemiological transition, do you believe the rise of NCDs is an unavoidable cost of development, or a preventable consequence of choices we are making today?

References

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC5648412/
2. https://www.thelancet.com/journals/langlo/article/PIIS2214-109X(23)00468-0/fulltext
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4. https://pmc.ncbi.nlm.nih.gov/articles/PMC1940110/
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC6380124/
6. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9552506/
7. https://www.frontiersin.org/journals/public-health/articles/10.3389/fpubh.2022.1079827/full
8. https://www.wbhealth.gov.in/NCD/
9. https://www.thinkglobalhealth.org/article/indias-call-action-noncommunicable-diseases
10. https://www.drishtiias.com/daily-updates/daily-news-editorials/the-burden-of-non-communicable-diseases-ncds-in-india