Persons with multiple chronic conditions are a large and growing segment of the US population. However, little is known about how chronic conditions cluster, and the ramifications of having specific combinations of chronic conditions. Clinical guidelines and disease management programs focus on single conditions, and clinical research often excludes persons with multiple chronic conditions. Understanding how conditions in combination impact the burden of disease and the costs and quality of care received is critical to improving care for the 1 in 5 Americans with multiple chronic conditions. This Medline review of publications examining somatic chronic conditions co-occurring with 1 or more additional specific chronic illness between January 2000 and March 2007 summarizes the state of our understanding of the prevalence and health challenges of multiple chronic conditions and the implications for quality, care management, and costs.KEY WORDS: chronic disease; comorbidity; prevalence; quality of health care.

Background Among patients with multiple chronic conditions, there is increasing appreciation of the complex interrelatedness of diseases. Previous studies have focused on the prevalence and economic burden associated with multiple chronic conditions, much less is known about the mortality rate associated with specific combinations of multiple diseases. Objective Measure the mortality rate in combinations of 11 chronic conditions. Design Cohort study of veteran health care users. Participants Veterans between 55 and 64 years that used Veterans Health Administration health care services between October 1999 and September 2000. Measurements Patients were identified as having one or more of the following: COPD, diabetes, hypertension, rheumatoid arthritis, osteoarthritis, asthma, depression, ischemic heart disease, dementia, stroke, and cancer. Mutually exclusive combinations of disease based on these conditions were created, and 5-year mortality rates were determined. Results There were 741,847 persons included. The number in each group by a count of conditions was: none = 217,944 (29.34%); 1 = 221,111 (29.8%); 2 = 175,228 (23.6%); 3 = 86,447 (11.7%); and 4+ = 41,117 (5.5%). The 5-year mortality rate by the number of conditions was: none = 4.1%; 1 = 6.0%; 2 = 7.8%; 3 = 11.2%; 4+ = 16.7%. Among combinations with the same number of conditions, there was significant variability in mortality rates. Conclusions Patients with multiple chronic conditions have higher mortality rates. Because there was significant variation in mortality across clusters with the same number of conditions, when studying patients with multiple coexisting illnesses, it is important to understand not only that several conditions may be present but that specific conditions can differentially impact the risk of mortality.

Trends in primary care practice reflect changes in society and in the US health care system, including demographic changes, an emphasis on prevention, and the growth of managed care. The increasing role of managed care, with its emphasis on increased productivity, appears at odds with primary care physicians' increasing responsibility for prevention and the associated increase in the duration of primary care visits.

This study analyzes how the growing proportion of women in the United States physician population will affect the amount and type of physician services available to the US population. Female physicians work fewer hours per week, are slightly less likely to be in patient care, and tend to enter different specialties than male physicians. Female physicians also have higher retirement rates than male physicians, but due to their lower mortality rates, have work lives nearly as long as male physicians. We examined how the changing composition of the physician population will affect the availability of physician services by comparing historical and pro-

Increasing prevalence of health systems and hospital managed care ownership may lead to higher quality but are unlikely to reduce hospital discharge costs. Encouraging participation in innovative payment and delivery reform models, such as accountable care organizations, may be more powerful options.