Infections of the upper respiratory tract (URIs) have a tremendous impact on public health. They are among the most common reasons for visits to primary care providers, and although the illnesses are typically mild, their high incidence and transmission rates place them among the leading causes of time lost from work or school. Even though a minority (~25%) of cases are caused by bacteria, URIs are the leading diagnoses for which antibiotics are prescribed on an outpatient basis in the United States, often inappropriately. Antibiotics are more often misprescribed in adults than in pediatric populations. The enormous consumption of antibiotics for these illnesses has contributed to the rise in antibiotic resistance among common community-acquired pathogens such as Streptococcus pneumoniae—a trend that in itself has an enormous influence on public health and on the individual patient.
Although most URIs are caused by viruses, distinguishing patients with primary viral infection from those with primary bacterial infection is difficult. Signs and symptoms of bacterial and viral URIs are typically indistinguishable. Until consistent, inexpensive, and rapid testing becomes available and is used widely, acute infections will be diagnosed largely on clinical grounds. The judicious use and potential for misuse of antibiotics in this setting pose ongoing challenges.
NONSPECIFIC INFECTIONS OF THE UPPER RESPIRATORY TRACT
Nonspecific URIs are a broadly defined group of disorders that collectively constitute the leading cause of ambulatory care visits in the United States. By definition, nonspecific URIs have no prominent localizing features. They are identified by a variety of descriptive names, including acute infective rhinitis, acute rhinopharyngitis/nasopharyngitis, acute coryza, and acute nasal catarrh, as well as by the inclusive label common cold.
The large assortment of URI classifications reflects the wide variety of causative infectious agents and the varied manifestations of common pathogens. Nearly all nonspecific URIs are caused by viruses spanning multiple virus families and many antigenic types. For instance, there are at least 100 immunotypes of rhinovirus (Chap. 194), the most common cause of URI (~30–40% of cases); other causes include influenza virus (three immunotypes; Chap. 195) as well as parainfluenza virus (four immunotypes), coronavirus (at least three immunotypes), and adenovirus (47 immunotypes) (Chap. 194). Respiratory syncytial virus (RSV), a well-established pathogen in pediatric populations, is also a recognized cause of significant disease in elderly and immunocompromised individuals. A host of additional viruses, including some viruses not typically associated with URIs (e.g., enteroviruses, rubella virus, and varicella-zoster virus), account for a small percentage of cases in adults each year. Although new diagnostic modalities (e.g., nasopharyngeal swab for polymerase chain reaction) can assign a viral etiology, there are few specific treatment options, and no pathogen is identified in a substantial proportion of cases. A specific diagnostic workup beyond a clinical diagnosis is generally unnecessary in an otherwise healthy adult.