Syndemics and Health

Merrill Singer is a medical anthropologist and emeritus professor of anthropology at the University of Connecticut. He specializes in environmental health and infectious diseases, and coined the term “syndemics” in 1992. He generously provided this backgrounder for Defining Moments Canada. 


Syndemic is a concept used among public health, health social science, and medical researchers to refer to the dangerous interaction of two or more diseases in a population and which leads to worse health outcomes. The term was formed by uniting “synergy” (the interaction or cooperation of two or more entities) and “emic” (a public health term that means `on the people’). 

An example of a syndemic is the 1918-1919 influenza pandemic, which involved interactions between diseases caused by two different kinds of microscopic pathogens — viruses and bacteria. Most deaths during that influenza pandemic were not caused by the influenza virus acting alone. Rather, victims generally succumbed to bacterial pneumonia following an initial influenza virus infection. The pneumonia was caused when various common bacteria that normally are limited to the nose and throat moved deep into an individual’s lungs along a bronchial tube pathway of cells that were killed by the influenza virus. 

Among the cells destroyed by the influenza virus were protective cells with hair-like projections, or “cilia,” that serve to move microbes and debris up and out of the airways, and then out of the body. The loss of these cells, with their protective function, made other kinds of cells throughout the entire respiratory tract — including those deep in the lungs — vulnerable to bacterial infection. 

These kind of changes in the body do not take place in a social vacuum. People are more vulnerable to infection if their immune systems have been weakened by stressful social conditions like poverty, discrimination, crowding, and stigmatization. Stress stimulates the body’s production of a hormone called cortisol, which helps the body cope with short-term experiences of stress. However, prolonged experience of stress, lasting from multiple days to years, can cause a build-up of certain hormones that compromise the effectiveness of the immune system. Also, because stress can harm sleep quality, people who do not get quality sleep or enough sleep are more likely to get sick after being exposed to a virus.

During a disease outbreak, morbidity and mortality rates are often also heightened by pre-existing differences and disparities in health and healthcare. Adverse social conditions are important in syndemics because they contribute to the formation, clustering, and spread of disease by increasing susceptibility, reducing the quality of the immune function, and limiting prevention and treatment. 

Syndemic interaction can involve multiple biological, psychological, and behavioral factors. Moreover, syndemics involve interaction between all types of diseases and health conditions, including infections, chronic non-communicable diseases, mental health problems, toxic environmental exposures, and malnutrition. 

There is growing recognition that many of the most damaging disease events in human history—from COVID-19 to HIV/AIDS, the Black Plague, and the European diseases that devastated North American Indigenous populations—are the probable consequence not of a single disease acting alone, but rather several diseases acting in tandem.


The term syndemic was first used by medical anthropologists during the height of the AIDS pandemic to characterize a tripartite health condition found among the inner-city poor. The researchers called this condition “SAVA.” SAVA involves the complex interactions among Substance Abuse, Violence, and AIDS. Researchers who coined the term syndemic were involved in studies of populations at very high risk of infection. These researchers realized it was necessary to go beyond seeing AIDS as a biological condition and rather looking at the full picture of the lives and other health problems of the people they were studying. 

From the syndemic perspective that developed from this research, the social contexts — substance abuse, violence, and AIDS in particular — are understood to be so entwined, and each condition is so significantly shaped by the presence of the other two, that it is incorrect to think of them as three distinct health problems. In SAVA, all three disease/health related components interact with one another. There are ways in which drug use interacts directly with AIDS, e.g., the spread of AIDS through the illicit injection of drugs like heroin and cocaine. Illicit drug injection has been found to promote the transmission of HIV, the virus responsible for AIDS. 

Similarly, violence and AIDS interact in mutually amplifying ways, such as when the risk of an HIV infection is heightened through domestic violence that prevents people from accessing health care, or, in the case of an AIDS patient, to adhere to prescribed treatment. Drugs and violence also propel each other, particularly through drug trade conflict. In addition to these interactions, SAVA syndemics are shaped by the local social context. Illicit drug users, for example, are commonly stigmatized by the wider society, are denied access to services, and tend not to have strong social support networks. 

The same is true among some members of the LGBTQ+ community. Mental health problems like anxiety and depression have been found to be a fourth component of SAVA in LGBTQ+ community, as well as in other oppressed subgroups. There are, in fact, multiple SAVA syndemics around the world, each driven by its own distinct configuration of populations, social conditions, and disease interactions.


In December, 2019, an outbreak of an infectious novel coronavirus disease (COVID-19) was first reported in Wuhan, China. Over the subsequent months, the outbreak has developed into a widespread and potentially deadly global pandemic with significant health, economic, and political consequences. The pandemic quickly overwhelmed health and public health services in heavily impacted areas. 

While initially an infection of animal origin, the coronavirus (also known as SARS-CoV-2) developed into an infectious agent transmitted person-to-person or through contact with contaminated surfaces or objects. A special risk of COVID-19 is that the disease can be spread by infected individuals who are not experiencing any symptoms at the time they are transmitting the disease to others. 

The coronavirus, which attacks both respiratory and heart cells, and possibly the cells of other organs, is most severe when it interacts with pre-existing respiratory, cardiovascular, and other noncommunicable diseases like asthma, diabetes, high blood pressure, and immune system disorders. In Canada, the most commonly reported pre-existing health conditions that interact adversely with COVID-19 are cardiac disease, respiratory disease, and diabetes. 

study of confirmed hospitalized patients from across China found that patients with any of these comorbidities had poorer clinical outcomes than those without them, and that the greater the number of other health problems suffered by COVID-19 patients, the less likely they were to recover.

Social factors like poverty, population density, inequality of access to health care, incarceration, and homelessness are emerging as likely facilitators of both illness and death in the pandemic. COVID-19 has had an especially harsh impact on Black people in North America. A CDC study of over 500 hospitalized people indicated that white patients were under-represented relative to the demographics of the surrounding community, whereas Black patients were significantly over-represented (33% of cases compared with 18% of the community). The disproportionate rates of severe COVID-19 symptoms and mortality in this population have been tied to health and healthcare disparities, as well as burdensome social conditions like poverty and systematic racism.

Another social factor shaping the COVID-19 pandemic is living in a nursing home or other long-term living facility. These institutions, home to many people with compromised immune systems, heart and lung problems, diabetes and other serious disorders, emerged as hotspots of COVID-19 infection. While nursing homes have become a standard form of care for millions of aged and incapacitated persons, this is only a relatively recent 20th century development. The original nursing homes were established to separate poorer white patients from ethnic minority and immigrant patients. The latter often were sent to almshouses with minimal medical and nursing care, and low sanitation and safety standards. 

In second example, SARS (Severe Acute Respiratory Syndrome), a disease also triggered by a coronavirus, became a global pandemic in 2003. SARS was a pneumonia-like disease that killed about one in every ten people who became infected. Ultimately, over 8,000 people from 29 countries and territories were infected with SARS before the pandemic ended in 2004, according to the CDC. Most of the infections in Canada occurred in Toronto hospitals or could be traced to hospital contacts. The outbreak led to the quarantine of thousands, and killed 44 people. SARS was found to be spread from person to person through coughing and sneezing by infected individuals, but not by simply exhaling, as occurs with COVID-19. 

Once it entered a person’s body, the SARS virus infected the protective “epithelial” cells of the lower respiratory system, causing damage to parts of the lung involved in gas exchange with the blood. People with diabetes who contracted SARS were at greater risk of dying, being admitted to intensive care units of hospitals, or having to be treated with a mechanical ventilator. Individuals with cardiopulmonary disease also were at heightened risk if infected. A study of SARS patients in Taiwan found that individuals over 65 with preexisting diabetes mellitus were more likely to develop acute respiratory distress symptoms. 

The SARS pandemic taught us a number of important lessons:

A third example is a disabling syndemic involving Type 2 diabetes and depression, and other health conditions as well. The term VIDDA syndemic was first used to label the complex interactions of Violence, Immigration, Depression, Diabetes and Abuse among first‐ and second‐generation Mexican immigrant women in Chicago. VIDDA refers to the ways in which political, economic, and social processes shape the clustering of depression and diabetes in this population. The term VIDDA highlights the fact that diabetes should not be seen in isolation from other non-medical factors, and further, that this syndemic is not limited to the interaction between diabetes and depression. Rather, these two diseases comprise a bio-social feedback loop in which they function as both contributors to, and consequences of, a stressful life. In this feedback loop, the burdens of limited income and diabetes cause prolonged stress, which, in turn, increases the risk of depression. One effect of depression among diabetes patients is poor self-management of the disease, which accelerates damage to the body. Experiences of this downward cycle are known as “syndemic suffering.” 

There are three ways in which diabetes and depression might come to be clustered together in a population: 

There is research to support each of these possibilities, although only the second and third cases constitute a syndemic as they involve disease interaction.


While the concept of syndemics was first used by medical anthropologists in the early 1990s, the scientific articles published in scholarly journals by these researchers attracted the attention of other social scientists concerned with diverse problems in various populations. Over the years, a burgeoning multidisciplinary public health and medical literature on syndemics has appeared. Enthusiasm about the usefulness of the syndemic framework contributed to a rapid increase in number of articles, chapters, PhD dissertations, and commentaries on syndemics in the scholarly literature. 

The health issues of populations studied from a syndemics perspective include illicit drug use; HIV-related problems among gay, lesbian, bisexual and transgender persons; asthma among farmworkers; childhood sexual abuse and other traumas; health conditions afflicting sex workers; and various health problems associated with poverty among marginalized groups, such as Indigenous peoples or incarcerated individuals; diabetes, malaria, and tuberculosis sufferers; tick-transmitted diseases, and mosquito-transmitted diseases, like Zika. 

Syndemic research has been carried out around the world, although most has been done in North America and Asia. In Canada in 2018, the Public Health Agency of Canada developed a national approach for dealing with Sexually Transmitted and Blood-Borne Infections. Known as the Pan-Canadian STBBI framework for action,” this syndemic strategy promotes an integrated, multiple disease approach, with a focus on the key populations that are affected by specific syndemics.


Considering health issues from a syndemic perspective creates the potential for governments and health institutions to shape both public health policy and medical practice. Syndemic thinking draws attention to the fact that health is not just a product of biology, genetics, or individual behaviors. Rather, health is shaped by the interaction of social, economic, and environmental factors. Further, the syndemic approach focuses attention on the distribution of diseases across a population, and acknowledges the stark differences between rich and poor sub-populations, as well as dominant and marginalized communities. 

An understanding of the patterns of disease that cluster in segments of a population, and the vulnerability of subgroups within the population, can guide efforts to minimize human suffering and prevent the spread of disease. This outlook becomes increasingly important as populations face growing health risks due to profound and widespread environmental changes, many of which are caused by human behavior. These changes are intensifying health and social disparities and promote syndemics. For example, climate change promotes the spread of disease vectors like mosquitos, ticks, and rodents. This ecological response to global warming results in new syndemic interactions among diseases that previously were geographically isolated from each other. Similarly, the quality of the air we breathe has significantly diminished over the last several decades as a result of the interaction of global warming with other forms of environmental degradation, such as air pollution. Consequently, there have been notable increases in the global frequency of a range of respiratory diseases, especially among poorer and disadvantaged populations in both developed and developing nations. As seen in the cases of SARS and COVID-19, the respiratory system is a primary body site for environmental disease threats to cluster, interact, and multiply their adverse impacts (e.g., diesel fuel droplets interact with allergens and air-borne pathogens). These growing threats to respiratory health are being amplified by global warming and are known as “ecosyndemics.”

Awareness of syndemics allows people to think about health in a new way and to better understand new pandemics like COVID-19 or the global influenza outbreak of 1918-1919.