Introduction to Syndemics: A Critical Systems Approach to Public and Community Health . Merrill Singer . San Francisco : Jossey-Bass , 2009 ; xxi + 274 pp .

In the early 1990s, Merrill Singer initiated and has since championed the use of the concept of “syndemic” to explain the cooccurrence of different infections or noncommunicable diseases, the interactions of the two (or more) diseases, and the association of poor health with social, cultural, economic, and physical environmental factors. The term is now widely used in public health and disease control settings. It provides a ready shorthand that acknowledges the interplay of the biological and the social, and that acknowledges too the interactions of diseases and pathogens at molecular, organic, and other systemic levels. Our understanding of these many interactions, and how they produce compounding illness, is poor. Singer's introductory book on syndemics is therefore timely.

Singer argues that social factors create the preconditions for syndemics and inhibit their resolution. Globalization and attendant urbanization; the exploitation of natural resources and changes in the physical environment; political and economic instability; and mass civil violence, interpersonal violence, racism, and social exclusion all contribute to create pathogenic environments. Infectious organisms and embodied responses are cultivated in such environments, and made virulent by the social structures that shape vulnerability and inhibit access to medical care and health services. To be blunt, poor people living in poorly resourced and unstable environments carry the burden of communicable and noncommunicable diseases and other health insults, which occur in individuals concurrently and that behave synergistically. These diseases interact biologically. In so doing, they produce greater morbidity and create greater risk of infection of yet more diseases. Their cooccurrence affects treatment also, although we know little of the pharmacological interactions in the treatments for many coinfections.

The interactive cooccurrence of HIV and tuberculosis is one of the best-known examples of these synergies, as Singer describes them. People infected with HIV are more likely than others to become infected with TB, for immunological and contextual reasons; people with TB are more likely to develop active disease if they become infected with HIV. TB is harder to diagnose in HIV-positive people, it progresses faster, and is more likely to be fatal. Early and effective treatment of TB infection is vital because of its infectivity, yet treatment can be complicated because of interactions between its medications and those for HIV. Treatment is complicated because of persistent stigma against the two diseases. Both conditions predominate among people who are poor, lack access to any health care, and often also have other infections and diseases (incl. many not diagnosed: e.g., undernutrition and parasitic infections resulting in anemia). Mental health problems—depression and anxiety especially—are endemic and underdiagnosed and untreated in these populations, further undermining the health of those affected and eroding their capacity to seek and adhere to treatment. Each social or medical condition compounds others. Syndemics are implosions in individual and social bodies.

Singer's book is a textbook. There are teaching and learning objectives at the beginning and key terms and discussion questions at the end of each chapter, with the general thread of argument in the chapters supported by examples (shaded) and case study notes. Yet as a text book, it falls short. It would have been stronger, for example, with recommended key readings at the end of chapters, and with the references bundled by topic rather than as a single combined list. It would have gained, too, from more tables, figures, and plates—there are a few tables only, not listed in the contents—and faculty would have gained from clearer directions of how to use this book for teaching. The writing could have been tighter, and the occasional typographic and other errors caught.

One error is worth comment. Singer refers to elephantiasis as a disease (pp. 94, 159, 211). Although still used popularly to refer to the disease, the term is descriptive of the frank symptoms of heavy parasitic filarial infection; the correct term is lymphatic filariasis (LF). LF is an excellent example of a disease that is endemic for social and structural reasons. Rapid city growth in many emerging economies has outpaced infrastructure, government capacity, and services. Although Singer does not elaborate, such cities create the ideal conditions for the vector, Culex mosquitoes, to continue to breed in drainage canals, septic pits, and other sources of stagnant water, and they provide the dense human population needed to maintain the lifecycle of the parasite. The example is valuable, too, because the environmental conditions that support Culex also support Aedes mosquitoes, which transmit dengue fever, and they support various water- and food-borne pathogens, resulting in the cooccurrence of dengue and these other related conditions often in the same populations that have high levels of HIV. I labor this point because the book is directed to public health and community health students, for whom such details of nomenclature, as well as the specific links of environment, governance, social organization, host, and vector, all matter.

As we have seen in the increasing use of the term epidemic to refer to noncommunicable conditions (e.g., obesity), so Singer has included in the term syndemic various conditions and behaviors often ignored by epidemiologists. His description of “SAVA”—substance abuse, violence, and AIDS (ch. 2)—is one example. But a couple of other examples come to mind, surprising in their omission. Anemia is one omitted condition indexical of syndemics: parasitic infection, food insecurity, poor nutrition, gender inequality, early age at first pregnancy, pregnancy and birth outcomes, and the future long-term health of surviving infants. Metabolic syndrome is another omitted condition: it offers an intriguing connective thread between overweight and obesity, stress, sedentary lifestyle, changes in production, food insecurity and diet, diabetes mellitus, cardiovascular health and chronic kidney disease, and social marginality and poverty. By arguing the interconnections of the epidemiology of disease, social structure, and political economy, Singer inspires us to find our own examples.

As noted, this book was written particularly for people teaching and training to work in public and community health, developing policy and designing, implementing and evaluating prevention and control programs. The elucidation of the interplay of biology and pathophysiology, in areas where we have data, are rich; but the book would have been stronger with more case study material of how specific aspects of social life, community, and political economy shape the development and evolution of various syndemics, and of ways to address health services and community challenges to syndemic prevention and control. Of course, intervention is problematic and complicated—this is the point of a syndemic approach. The copresence of different diseases are compounded by poverty and inequality, yet programs for prevention, intervention, control, and treatment access all tend to be targeted, not global. A syndemic approach could change this. Certainly this book is rich in examples, will prove provocative and stimulating discussion as it is used, and will be highly influential in the approaches that will be taken by public health professionals in the future.