Epidemiology

Cough is the single most common symptom for which patients worldwide seek medical attention. Cough is an important respiratory symptom because it can not only sometimes suggest serious underlying medical conditions but also cause serious complications and significantly affect a patient’s lifestyle and sense of well-being.

Questionnaire surveys have estimated the prevalence of cough to be as high as 9% to 33% of the population. With prevalence this high and the seriousness with which it is regarded by patients, it is not surprising that cough was the most frequent symptom for ambulatory care visits in 2001 to 2002 in the United States, accounting for 3.1% of visits. In the United States alone, 2006 sales for over-the-counter cough and cold remedies exceeded $3.6 billion. Guidelines to help health care providers diagnose and manage cough have been published in North America, Europe, South America, and Asia. reflecting its magnitude and importance to medical care around the world. To help even more patients with this common symptom, efforts have been made to develop an online service for diagnosing and advising patients experiencing cough.

Complications of cough

Cough is a respiratory reflex mediated by sensory afferents of the vagus nerve. It is an important respiratory clearance mechanism that is stimulated by inflammatory and mechanical irritation of the airways and is especially important when normal mucociliary transport mechanisms are overwhelmed or inadequate. Atelectasis, pneumonia, lung abscess, bronchiectasis, and pulmonary fibrosis may occur when cough is ineffective in its protective role.

An individual cough typically has three main phases: a brief inspiratory phase; a compressive phase, in which the glottis closes and intrathoracic pressure builds as a result of expiratory muscle contraction; and, finally, an expiratory phase, which involves opening of the glottis and a sudden release of air at high velocity. Cough effectiveness depends primarily on achieving a high expiratory air flow and a high linear velocity of the air column. The high intrathoracic pressures (up to 300 mm Hg) achieved during the expiration phase and high velocities of airflow (up to 500 miles per hour) during vigorous coughing can cause various cardiovascular, central nervous system, gastrointestinal, musculoskeletal, respiratory, and miscellaneous complications, many of which can be serious, including syncope, rib fractures, and pneumothoraces ( Box 1 ).

One important and common complication of chronic cough is a significant decrease in quality of life stemming from both psychological and physical adverse occurrences such as fear of serious illness, self-consciousness in social situations, urinary incontinence, and other functional impairments. The marked decrease in health-related quality of life is likely responsible for cough being the most common symptom bringing patients to medical attention.

Complications of cough

Cough is a respiratory reflex mediated by sensory afferents of the vagus nerve. It is an important respiratory clearance mechanism that is stimulated by inflammatory and mechanical irritation of the airways and is especially important when normal mucociliary transport mechanisms are overwhelmed or inadequate. Atelectasis, pneumonia, lung abscess, bronchiectasis, and pulmonary fibrosis may occur when cough is ineffective in its protective role.

An individual cough typically has three main phases: a brief inspiratory phase; a compressive phase, in which the glottis closes and intrathoracic pressure builds as a result of expiratory muscle contraction; and, finally, an expiratory phase, which involves opening of the glottis and a sudden release of air at high velocity. Cough effectiveness depends primarily on achieving a high expiratory air flow and a high linear velocity of the air column. The high intrathoracic pressures (up to 300 mm Hg) achieved during the expiration phase and high velocities of airflow (up to 500 miles per hour) during vigorous coughing can cause various cardiovascular, central nervous system, gastrointestinal, musculoskeletal, respiratory, and miscellaneous complications, many of which can be serious, including syncope, rib fractures, and pneumothoraces ( Box 1 ).

One important and common complication of chronic cough is a significant decrease in quality of life stemming from both psychological and physical adverse occurrences such as fear of serious illness, self-consciousness in social situations, urinary incontinence, and other functional impairments. The marked decrease in health-related quality of life is likely responsible for cough being the most common symptom bringing patients to medical attention.

Classifying cough according to duration

Classifying cough based on its duration helps narrow diagnostic possibilities, is a widely accepted approach to differential diagnosis, and is the foundation of strategies described in consensus guidelines around the world. Cough is categorized as either acute (ie, lasting <3 weeks); subacute (ie, lasting 3–8 weeks); or chronic (ie, lasting >8 weeks). Acute cough is usually transient, of minor consequence, and most commonly caused by the common cold, although it can occasionally be associated with life-threatening conditions, such as pulmonary thromboembolism, congestive heart failure, and pneumonia.

The category of subacute cough is most commonly a postinfectious phenomenon in which cough develops during a respiratory infection that is more severe than an uncomplicated common cold (eg, pertussis) and then resolves spontaneously within 8 weeks. When cough persists beyond 3 weeks without any obvious respiratory infection, guidelines recommend beginning the workup for chronic cough even before 8 weeks, because it probably will not resolve on its own.

Differential diagnosis for acute cough

Upper respiratory tract infections, especially the common cold, are the most common causes of acute cough ( Table 1 ). The prevalence of cough in patients who have untreated common colds ranges from 83% during the first 48 hours to 26% at day 14. During that 14-day period, the prevalence of cough as a symptom progressively decreases, similar to that of other symptoms associated with the common cold, such as sensation of postnasal drip, throat clearing, nasal obstruction, and nasal discharge.

The diagnosis of the common cold is usually straightforward when immunocompetent patients present with an acute upper respiratory illness characterized by symptoms and signs referable predominantly to the nasal passages (eg, rhinorrhea, sneezing, nasal obstruction, postnasal drip). Patients may or may not have fever, lacrimation, and throat irritation, and physical examination of the chest is normal. In this setting, diagnostic testing has a low yield, with chest roentgenograms being normal in greater than 97% of cases. However, with acute cough in immunocompromised patients, especially those who have AIDS or are at risk for developing AIDS, the clinician should address pneumonia secondary to Pneumocystis jiroveci and Mycobacterium tuberculosis early in the evaluation, even if the physical examination and chest roentgenogram are normal.

Acute cough is also commonly caused by allergic rhinitis, acute bacterial sinusitis, acute exacerbation of asthma or chronic obstructive pulmonary disease, and the initial catarrhal stage of Bordetella pertussis infection. Acute cough also can be the presenting manifestation of pneumonia, congestive heart failure, pulmonary thromboembolism, or conditions that predispose to aspiration. Approximately 50% of patients who have documented pulmonary thromboembolism complain of cough, and cough is occasionally the predominant complaint. In evaluating patients who have acute cough, clinicians must decide whether the patient has a life-threatening condition (eg, pneumonia or pulmonary thromboembolism) or not (eg, common cold) and conduct further evaluation and management accordingly.

Differential diagnosis for subacute cough

The main diagnostic distinction to make when evaluating subacute cough is whether the cough is postinfectious (see Table 1 ). Postinfectious cough begins during an acute respiratory tract infection that is not complicated by pneumonia and that ultimately resolves without treatment. The most common causes are viral infections, B pertussis infection, bacterial sinusitis, and exacerbations of preexisting diseases, such as asthma, chronic bronchitis, or bronchiectasis. For a cough that has persisted for 3 to 8 weeks but did not begin during an obvious upper respiratory tract infection, the most common causes are the same as for chronic cough (see below).

Infection with B pertussis is one cause of postinfectious cough and is a diagnosis suggested by recent B pertussis infections in the community, a patient’s history of contact with a known case, a cough with a biphasic course (ie, worsening after initial improvement), or a characteristic “whoop” or cough–vomit syndrome. Of course, a biphasic course for cough should lead physicians to consider other causes of cough, such as flares in asthma, chronic bronchitis, and bronchiectasis, but classically B pertussis infection should always be considered when cough follows a biphasic course.

After a 1- to 3-week incubation period, a catarrhal phase occurs consisting of conjunctivitis, rhinorrhea, fever, malaise, and cough, followed by a paroxysmal phase featuring worsening of the cough. Cough from pertussis usually lasts 4 to 6 weeks, but may persist for months. Laboratory confirmation of B pertussis in a clinical setting can be difficult to establish because a delay usually occurs between onset of cough and suspicion of the disease. No reliable serologic test for B pertussis is readily available. Cultures of nasopharyngeal secretions are usually negative beyond 2 weeks of infection, and confirmatory serologic testing requires paired acute and convalescent sera samples. Polymerase chain reaction tests for B pertussis have not yet been standardized. The U.S. Advisory Committee on Immunization Practices has recommended dTap vaccine for adolescents and adults up to 65 years of age, reflecting the frequency and importance of this highly transmittable disease.

Acute bronchitis can result in subacute cough, but the diagnosis should only be made when the clinician has excluded pneumonia, the common cold, acute asthma, and, in smokers, an exacerbation of chronic bronchitis. Viral cultures, serologic assays, and sputum analysis should not be performed routinely for acute bronchitis.