Syndemic

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Syndemics combine the synergies of epidemics to evaluate how social and health conditions travel together, in what ways they interact, and what upstream drivers may produce their interactions.[1] The idea of syndemics is that no disease exists in isolation and that often population health can be understood through a confluence of factors (such as climate change or social inequality) that produces multiple health conditions that afflict some populations and not others.[2] Syndemics are not like pandemics (where the same social forces produce clustered conditions equally around the world); instead, syndemics reflect population-level trends within certain states, regions, cities, or towns.[3][4]

A syndemic or

health disparity, caused by poverty, stress, climate, or structural violence and are studied by epidemiologists and medical anthropologists concerned with public health, community health and the effects of social conditions on health. The concept was translated from anthropology to a larger audience in 2017, with the publication of a Series on Syndemics in The Lancet, led by Emily Mendenhall.[6]

The syndemic approach departs from the biomedical approach to diseases to diagnostically isolate, study, and treat diseases as distinct entities separate from other diseases and independent of social contexts.

Definition

A syndemic is a

synergistic epidemic. The term was developed by Merrill Singer in the mid-1990s, culminating in a 2009 textbook.[7] Disease concentration, disease interaction, and their underlying social forces are the core concepts.[8]
Disease co-occurrence, with or without interactions, is known as comorbidity and coinfection. The difference between "comorbid" and "syndemic" is per Mustanski et al.[9][10] "comorbidity research tends to focus on the nosological issues of boundaries and overlap of diagnoses, while syndemic research focuses on communities experiencing co-occurring epidemics that additively increase negative health consequences." It is possible for two afflictions to be comorbid, but not syndemic i.e., the disorders are not epidemic in the studied population, or their co-occurrence does not cause an interaction that then contributes to worsened health. Two or more diseases can be comorbid without interactions, or interaction occurs but it is beneficial, not deleterious. Syndemic theory seeks to draw attention to and provide a framework for the analysis of adverse disease interactions, including their causes and consequences for human life and well-being.[11] Although the majority of this research has focused on HIV,[12] an emerging body of work on syndemics has expanded to other co-occurring conditions.[13][14]

Syndemic Methods: from historical archives to mathematical models

Methods for evaluating syndemics have been a focus on scholarship for deepening the application of what has largely served as theory to understand why and how social and health conditions cluster together, interact, and are driven by shared forces, from climate (such as escalation of heat, rain, drought, and events) to poverty (such as food insecurity, poor housing, lack of safety, and limited work opportunities).[15] In 2022, Alexander Tsai (an epidemiologist), Emily Mendenhall (a medical anthropologist), and Timothy Newfield (a historian) teamed up on a Special Issue in Social Science and Medicine to explore the various methodological ways in which syndemics can be understood, interpreted, and evaluated through history.[16] For instance, historical syndemics may be evaluated using archival data that is incomplete but provides a novel way of thinking about disease biography.[17] This is exemplified by Dylann Atcher Proctor's historical work on gastrointestinal distress in Gabon using historical archives that had never yet been evaluated on their own or synergistically.[18]

Ethnographic data provides a deeper understanding of how and why larger social forces produce disease clusters and interactions and are crucial for understanding "why" syndemics occurr. Ethnographic insights have served as the bedrock of syndemic thinking since Merrill Singer's pioneering intellectual and practical work with the concept beginning in the 1990s. His first article based on ethnographic thinking about the SAVA Syndemic came from real time observations as the AIDS epidemic that unfolded in tandem with substance use amidst structural violence in urban America throughout the 1990s and early 2000s.[19] Singer demonstrated how it was impossible to think about one condition without contextualizing the broader social, structural, and health contexts in which people lived. Discussion of ethnographic methods were detailed in Emily Mendenhall's books Syndemic Suffering[20] and Rethinking Diabetes[21] and is also exemplified in Mac Marshall's book Drinking Smoke.[22]

The largest body of methodological scholarship has emerged around the utility of epidemiological data.[23] Epidemiological data provides opportunities to investigate the synergistic ways in which diseases emerge and interact with social and health conditions.[24] This latter method has been the focus of contention, particularly in dialogue between Alexander Tsai and Ronald Stall.[25][26] Early epidemiological studies, for example, evaluated the ways in which social and health conditions co-occurred. Tsai argued that instead, there is a deeper need to interrogate how conditions syngistically interact to cause more adverse health conditions that the conditions would produce on their own. This has led to a slough of emergent research interrogating mathematical models that can take seriously how health conditions may cluster together and interact to affect the health and well being of populations residing in a specific nation, region, city, or town. A particularly useful model based on the Soweto Syndemics study was published in Nature Human Behavior.[27] In particular, spatial models for thinking through syndemic clusters, such as using GIS, are an emerging area of interest in syndemics research.[28][29]

Types of disease interaction

Diseases regularly interact and this interaction influences disease course, expression, severity, transmission, and diffusion. Interaction among diseases may be both indirect (changes caused by one disease that facilitate another through an intermediary) and direct (diseases act in direct tandem).[citation needed]

  • One disease can assist the
    physical transmission of the microbe causing another disease, for example, genital-tract ulceration caused by syphilis allowing sexual transmission of HIV.[citation needed
    ]
  • One disease may enhance the virulence of another, as for example, herpes simplex virus co-infection exacerbates HIV infection with progression to AIDS,[citation needed] periodontal bacteria may enhance the virulence of herpesvirus,[citation needed] HIV-infected individuals are more susceptible to tuberculosis; As of 2011, the cause was not fully understood.[30][31][32]
  • Changes in biochemistry or damage to organ systems, as for example diabetes weakening the immune system, promotes the progression of another disease, SARS.[citation needed]
  • A
    pneumococcus, causes excess mortality from secondary bacterial pneumonia during influenza epidemics. Influenza virus alters the lungs in ways that increase the adherence, invasion and induction of disease by pneumococcus, alters the immune response with weakened ability to clear pneumococcus or, alternately amplifying the inflammatory cascade.[33]
  • Direct interaction of diseases occurs in the case of genetic recombination among different pathogens, for instance between Avian sarcoma leukosis virus and Marek's disease virus (MDV) in domestic fowl.[citation needed] Both cancer-causing viruses are known to infect the same poultry flock, the same chicken, and, even the same anatomic cell. In coinfected cells, the retroviral DNA of the avian leukosis virus can integrate into the MDV genome, producing altered biological properties compared to those of the parental MDV. The frequency of gene reassortment among human pathogens is less clear than it is the among plant or animal species but of concern as animal diseases adapt to human hosts and as man new diseases comes into contact.[citation needed]
  • When one disease diminishes or eradicates another it is a counter-syndemic disease interaction.[citation needed]
  • The linkage also may not be clear, despite apparent syndemic interactions among diseases, as for example in type 2 diabetes mellitus and hepatitis C virus infection.[citation needed]

Iatrogenic

The term

adenovirus type 5 had a higher risk of HIV infection. The vaccine was created using a replication-defective version of Ad5 as a carrier, or delivery vector, for three synthetically produced HIV genes. On November 6, 2007, Merck & Co. announced that research had been stopped suspecting the higher rate of HIV infection among individuals in the vaccinated was because the vaccine lowered defenses against HIV.[citation needed
]

Examples

Various syndemics though not always labeled as such have been described in the literature, including:

19th century Native American

Contact between Native Americans and Europeans during the

Columbian Exchange led to lethal syndemics within the Native American population due to diseases introduced which the Native Americans had not encountered before and had not built-up immunity to.[citation needed
]

An example of a syndemic from the 19th century can be found on the reservations on which Native Americans were confined with the closing of the U.S. frontier. It is estimated that in 1860 there were well over 10 million

Pertussis, in rapid succession and with terrible fatal results..." Similarly, the Handbook of American Indians notes, "The least hopeful conditions in this respect prevail among the Dakota [Sioux] and other tribes of the colder northern regions, where pulmonary tuberculosis and scrofula are very common... Other more common diseases, are various forms of, bronchitis ...pneumonia, pleurisy, and measles in the young. Whooping cough is also met with." Indian children were removed to white boarding schools and diagnosed with a wide range of diseases, including tuberculosis, trachoma, measles, smallpox, whooping cough, influenza, and pneumonia.[citation needed
]

The Sioux were victims of a syndemic of interacting infectious diseases including the

1889–1890 flu pandemic, inadequate diet, and stressful and extremely disheartening life conditions, including outright brutalization with events like the massacre at Wounded Knee in 1890 and the murder of their leader Sitting Bull. While the official mortality rate on the reservation was between one and two percent, the death rate was probably closer to 10 percent.[citation needed
]

Influenza

There were three influenza

pandemics during the 20th century that caused widespread illness, mortality, social disruption, and significant economic losses. These occurred in 1918, 1957, and 1968. In each case, mortality rates were determined primarily by five factors: the number of people who became infected, the virulence of the virus causing the pandemic, the speed of global spread, the underlying features and vulnerabilities of the most affected populations, and the effectiveness and timeliness of the prevention and treatment measures that were implemented.[citation needed
]

The

1957 pandemic
was caused by the Asian influenza virus (known as the H2N2 strain), a novel influenza variety to which humans had not yet developed immunities. The death toll of the 1957 pandemic is estimated to have been around two million globally, with approximately 70,000 deaths in the United States. A little over a decade later, the comparatively mild Hong Kong influenza pandemic erupted due to the spread of a virus strain (H3N2) that genetically was related to the more deadly form seen in 1957. The pandemic was responsible for about one million deaths around the world, almost 34,000 of which were in the United States. In both of these pandemics, death may not have been due only to the primary viral infection, but also to secondary bacterial infections among influenza patients; in short, they were caused by a viral/bacterial syndemic (but see Chatterjee 2007).

The worst of the 20th-century influenza pandemics was the

H1N1 viral strain) pandemic in the single year of 1918 than during all four-years of the Black Death. The pandemic had devastating effects as disease spread along trade and shipping routes and other corridors of human movement until it had circled the globe. In India, the mortality rate reached 50 per 1,000 population. Arriving during the closing phase of World War I, the pandemic impacted mobilized national armies. Half of U.S. soldiers who died in the "Great War," for example, were victims of influenza. It is estimated that almost 3⁄4 of a million Americans died during the pandemic. In part, the death toll during the pandemic was caused by viral pneumonia characterized by extensive bleeding in the lungs resulting in suffocation. Many victims died within 48 hours of the appearance of the first symptom. It was not uncommon for people who appeared to be quite healthy in the morning to have died by sunset. Among those who survived the first several days, however, many died of secondary bacterial pneumonia. It has been argued that countless numbers of those who expired quickly from the disease were co-infected with tuberculosis, which would explain the notable plummet in TB cases after 1918.[citation needed
]

Climate change

As a result of the floral changes produced by global warming, an escalation is occurring in global rates of allergies and asthma. Allergic diseases constitute the sixth leading cause of chronic illness in the United States, impacting 17 percent of the population. Asthma affects about 8 percent of the U.S. population, with rising tendency, especially in low income, ethnic minority neighborhoods in cities. In 1980 asthma affected only about three percent of the U.S. population according to the U.S. CDC. Asthma among children has been increasing at an even faster pace than among adults, with the percentage of children with asthma going up from 3.6 percent in 1980 to 9 percent in 2005. Among ethnic minority populations, like Puerto Ricans the rate of asthma is 125 percent higher than non-Hispanic white people and 80 percent higher than non-Hispanic black people. The asthma prevalence among American Indians, Alaska Natives and black people is 25 percent higher than in white people.[citation needed]

Air pollution

Increases in asthma rates have occurred despite improvements in air quality produced by the passage and enforcement of clean air legislation, such as the U.S. Clean Air Act of 1963 and the Clean Air Act of 1990. Existing legislation and regulation have not kept pace with changing climatic conditions and their health consequences. Compounding the problem of air quality is the fact that air-borne pollens have been found to attach themselves to diesel particles from truck or other vehicular exhaust floating in the air, resulting in heightened rates of asthma in areas where busy roads bisect densely populated areas, most notably in poorer inner-city areas.

For every elevation of 10 μg/m3 in

particulate matter concentration in the air a six percent increase in cardiopulmonary deaths occurs according to research by the American Cancer Society. Exhaust from the burning of diesel fuel is a complex mixture of vapors, gases, and fine particles, including over 40 known pollutants like nitrogen oxide and known or suspected carcinogenic substances such as benzene, arsenic, and formaldehyde. Exposure to diesel exhaust irritates the eyes, nose, throat and lungs, causing coughs, headaches, light-headedness and nausea, while causing people with allergies to be more susceptible allergy triggers like dust or pollen. Many particles in disease fuel are so tiny they are able to penetrate deep into the lungs when inhaled. Importantly, diesel fuel particles appear to have even greater immunologic effects in the presence of environmental allergens than they do alone. "This immunologic evidence may help explain the epidemiologic studies indicating that children living along major trucking thoroughfares are at increased risk for asthmatic and allergic symptoms and are more likely to have respiratory dysfunction." according to Robert Pandya and co-workers.[citation needed
]

The damaging effects of diesel fuel pollution go beyond a synergistic role in asthma development. Exposure to a combination of microscopic diesel fuel particles among people with high blood cholesterol (i.e.,

strokes as well.[citation needed
]


A Note on Mathematical Models

A

Mathematical modelling in epidemiology is now being applied to syndemics.[citation needed
]

For example, modelling to quantify the syndemic effects of malaria and HIV in sub-Saharan Africa based on research in Kisumu, Kenya researchers found that 5% of HIV infections (or 8,500 cases of HIV since 1980) in Kisumu are the result of the higher HIV infectiousness of malaria-infected HIV patients. Additionally, their model attributed 10% of adult malaria episodes (or almost one million excess malaria infections since 1980) to the greater susceptibility of HIV infected individuals to malaria. Their model also suggests that HIV has contributed to the wider geographic spread of malaria in Africa, a process previously thought to be the consequence primarily of global warming.[49] Modelling offers an enormously useful tool for anticipating future syndemics, including eco-syndemic, based on information about the spread of various diseases across the planet and the consequent co-infections and disease interactions that will result.[50]

PopMod is a longitudinal population tool developed in 2003 that models distinct and possibly interacting diseases. Unlike other life-table population models, PopMod is designed to not assume the statistical independence of the diseases of interest. The PopMod has several intended purposes, including describing the time evolution of population health for standard demographic purposes (such as estimating healthy life expectancy in a population), and providing a standard measure of effectiveness for health interventions and cost-effectiveness analysis. PopMod is used as one of the standard tools of the World Health Organization's (

WHO) CHOICE (Choosing Interventions that are Cost-Effective) program, an initiative designed to provide national health policymakers in the WHO's 14 epidemiological sub-regions around the world with findings on a range of health intervention costs and effects.[51]

Future research

First, there is a need for studies that examine the processes by which syndemics emerge, the specific sets of health and social conditions that foster multiple epidemics in a population and how syndemics function to produce specific kinds of health outcomes in populations.[

global warming
contributes to the spread of diseases and new disease interactions. There is a need for a better understanding of how public health systems and communities can best respond to and limit the health consequences of syndemics. Systems are needed to monitor the emergence of syndemics and to allow early medical and public health responses to lessen their impact. Systematic ethno-epidemiological surveillance with populations subject to multiple social stressors must be one component of such a monitoring system.

See also

  • Endemic
  • List of epidemics
  • List of human diseases associated with infectious pathogens

References

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Further reading

Books

  • Marshall, Mac 2013 Drinking Smoke: The Tobacco Syndemic in Oceania. Honolulu, HI: University of Hawaiʻi Press.
  • Mendenhall, Emily 2012 Syndemic Suffering: Social Distress, Depression, and Diabetes among Mexican Immigrant Women. Left Coast Press, Inc.
  • Singer, Merrill 2009 Introduction to Syndemics: A Critical Systems Approach to Public and Community Health. San Francisco, CA: Jossey-Bass.

Articles, chapters

External links
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