New or unexplained symptoms account for about half of all office visits; the remainder of visits are for ongoing care of established medical conditions. Evidence-based symptom evaluation combines knowledge of a symptom's clinical epidemiology with disease candidates according to Bayesian principles, such that the likelihood of a specific disease is a function of patient demographics, comorbidities, and clinical features. This knowledge can help support decisions about further testing or treatment or whether to perform additional testing before treatment, or to treat without further testing.
In addition to epidemiologic factors, biological, psychological, social, and cultural factors affect how patients experience, interpret, and describe symptoms. Patients differ in deciding when symptoms are sufficiently bothersome or worrisome to cause them to seek medical attention, and in what they expect from the office visit.
The shift toward evidence-based principles of medicine, which encourages narrow study questions in homogeneous study populations, inadvertently ignores syndromes that are not readily explained by current biomedical models of disease. Conversely, even when the cause of a disease is known, host and environmental factors can influence the symptoms that are manifested. For example, in 1967, Evans proposed five "realities" that reflect the conundrum clinicians face when associating an acute respiratory syndrome with an etiologic pathogen: (1) The same clinical syndrome may be produced by a variety of infectious pathogens; (2) the same pathogen may produce a variety of syndromes; (3) the most likely cause of a syndrome may vary by patient age, year, geography, and setting; (4) diagnosis of the pathogen is frequently impossible on the basis of clinical findings alone; and (5) the causes of a large proportion of infectious disease syndromes are still unknown.
Age, tobacco use history, and duration of cough.
Dyspnea (at rest or with exertion).
Vital signs (heart rate, respiratory rate, body temperature).
Chest radiography when unexplained cough lasts more than 3–6 weeks.
Cough adversely affects personal and work-related interactions, disrupts sleep, and often causes discomfort of the throat and chest wall. Most people seeking medical attention for acute cough desire symptom relief; few are worried about serious illness. Cough results from stimulation of mechanical or chemical afferent nerve receptors in the bronchial tree. Effective cough depends on an intact afferent–efferent reflex arc, adequate expiratory and chest wall muscle strength, and normal mucociliary production and clearance.
Distinguishing acute (less than 3 weeks), persistent (3–8 weeks), and chronic (more than 8 weeks) cough illness syndromes is a useful first step in evaluation. Postinfectious cough lasting 3–8 weeks has also been referred to as subacute cough to distinguish this common, distinct clinical entity from acute and chronic cough.
In healthy adults, most acute cough syndromes are due to viral respiratory ...