elements are shared with public health (e.g., epidemiology and biostatistics), and many are shared with other fields of medicine. Primary care practice uses a unique blend of these knowledge bases, skills, and communication style. This chapter, without attempting to be exhaustive, describes further the content and characteristics of primary care.
The committee's definition of primary care stresses that primary care clinicians address a large majority of the problems people bring to the health care system. The content of primary care has been described in multiple ways, and the committee examined data from national surveys conducted in the United States and other countries. Glimpses of primary care can be appreciated by considering reasons for visits and the range of problems addressed by various clinicians.
The National Ambulatory Medical Care Survey (NAMCS) samples office visits to physicians and provides information on type of physician, the patient's stated reason for visit, the diagnosis, interventions, and so forth. Rosenblatt et al. (1995) using NAMCS data from 1989 and 1990 has characterized the content of nonreferred ambulatory visits to office-based physicians in the United States as diagnostic clusters. These clusters incorporate the problems people choose to bring to the health care system. They have remained stable over time and approximate the content of primary care practice.
The 20 diagnostic clusters shown in Table 4-1 (in rank order by frequency) incorporate just over half of nonreferred visits to U.S. physicians. They cover a spectrum of conditions that are not confined to a particular organ system, gender, or age group. They include acute and chronic problems, diseases and syndromes, mental health concerns and trauma, and visits focused on prevention. All of the clusters reflect problems whose solutions could have a considerable impact on the health of individuals and for which people expect expert care. They are neither trivial in their importance nor simple in terms of their diagnosis and management.
Figure 4-1 shows the portion of care for these clusters that is provided by three types of physicians: family physicians, internists, and pediatricians. Other physicians provide the remaining 10 percent or so of visits associated with a given diagnostic cluster. These specialties include orthopedists for sprains, strains, low back pain, and degenerative joint disease, and obstetricians for general medical examinations and urinary tract infections.
Although the NAMCS data display the most common diagnostic clusters, the distribution of visits by cluster cannot convey the level of complexity or severity of problems seen in primary care. Some indication of this complexity has been provided by Barondess (1982), who reviewed consecutive visits to his practice of