Chronic cough defined as daily cough for 3 to 4 weeks likely has been experienced by more than 50% of the pediatric population at some time during the first 18 years of life. This can be explained by the variable prevalence of disorders associated with chronic cough. For example, in the United States, as many as 8.9 million children younger than 17 years of age were purported to have had a diagnosis of asthma in 2001 (NCHS data, Centers for Disease Control and Prevention). Asthma varies in prevalence by age, race, and exposure (infectious, environmental) in the United States. In children, using physician diagnosed asthma alone as an indicator of cough largely under-predicts its prevalence. In a study of Alaskan Native children, physician diagnosis of asthma missed more than 30% of children with self-reported symptoms of chronic cough.

The U.S. National Health Interview Survey of 1996 estimated that 16 of every 100 children younger than 18 years of age experienced an episode of acute bronchitis. Of these episodes, more than 90% were medically attended and their illness was accompanied by restricted activity days (average of 13 to 29 days dependent upon age at presentation). Most clinicians describe acute bronchitis as a febrile illness with cough, rhonchi, and referred breath sounds. Hence, simple lower respiratory tract infections (LRTIs) are common findings and likely to be associated with chronic cough as defined previously.

In a study of children with recurrent LRTIs, as many as 42% of those younger than 18 months of age had silent GERD by scintigraphy. Evaluation of children older than 18 months of age, when physiologic reflux can be excluded, still reported silent GERD in 27%. Hence, the risk for GERD being associated with chronic cough symptoms is a common occurrence in older toddlers and children.

Parental smoking has been reported to cause chronic cough in children; children with two parents who smoke are reported to have a chronic cough prevalence of over 50%. Since lung function does not fully mature until school age, the impact of acute and long-term pollution exposure has been carefully studied in children. U.S. investigators identified higher death rates in infants from 1 to 12 months of age when inhaled particulate matter of less than 10 mm was sustained at high levels. Studies have documented diminished lung function and bronchitic symptoms including chronic cough following long-term exposure in Polish, Austrian, and U.S. children.

Some of the chronic disorders associated with chronic cough have a defined genetic link and fewer individuals are impacted than as with LRTIs or asthma. Examples include cystic fibrosis estimated to occur in 1 in 2,500 North Americans of European ancestry. Primary immune deficiency disorders may vary from 1 in 300 with selective IgA deficiency to 1 in 200,000 with severe combined immune deficiency. Disorders with lesser prevalence, such as foreign body aspiration, may have significant morbidity that can be prevented with early detection and sensitive diagnostic tools. The use of such epidemiologic data is important as it can allow the clinician to develop a logical pattern for evaluation of chronic cough based on family history, individual clinical symptoms/examination, and disease likelihood.

Cough is intended to clear the airway of mucus and external debris and is a normal host response. The cough reflex involves forceful exhalation caused by the contraction of expiratory muscles against a closed glottis. Gas is expelled at high velocity, and matter is moved toward the oral cavity. Neural pathways, the cortex, and the brainstem control the cough reflex. This reflex may become exaggerated in cough-associated disorders as a result of increased particulate matter in the airway.

Chronic cough is usually more worrisome to caregivers than to health care providers. Data suggest that parental and teacher reports of childhood cough may not always correlate with severity or even frequency of disease. Clinical presentation varies according to the associated disorder. For infectious agents, timing of cough, history of affected family members, and concurrent systemic symptoms may serve as important differentiators in the evaluation. In acute bronchitis, fever and cough almost invariably occur in connection with upper respiratory congestion (predominantly nasal). The patients’ temperatures can range from 37° to 39°C (100° to 103°F). Usually, cough is dry, harsh, and without sputum production in young infants. Coughing can be accompanied by gagging and vomiting, leading to poor oral intake and dehydration. Occasionally, older children with persistent cough will produce sputum and may complain of chest-wall pain. Usually, the clinical illness is preceded by 24 to 48 hours of lassitude or malaise. Subsequently, fever and cough develop; these symptoms may persist for as long as 1 week. A relatively slow recovery phase, spanning 1 to 2 weeks, with persistent cough is characteristic. Secondary bacterial infection can complicate the recovery period, causing exacerbation of fever and other clinical findings.

Chronic bronchitis is an uncommon occurrence in children but when present is characterized by excessive production of mucus and by cough that is present on most days for a minimum of 3 months per year. Fever can accompany the cough, and the temperature can range from 37°C to 39°C (100F° to 103°F). Establishing a distinction between this typically infectious disorder and asthma may be difficult. Asthma, or reversible obstructive airway disease, can be distinguished by the patients’ clinical response to the administration of traditional bronchodilators. Clinical symptoms of asthma may include persistent cough or audible spontaneous wheezing, which may be precipitated by upper respiratory infection/occult or symptomatic sinusitis, environmental exposures including airborne pollens, indoor allergens (animal dander, mites), weather changes, or irritants (strong odors, smoking). Exercise, stress, and undetected/untreated reflux are also well known to exacerbate childhood asthma. Night-time cough may be a common clinical presentation for the child with asthma and associated reflux.

Persistent LRTIs (e.g., pertussis) and Chlamydia and Mycobacterium infections can present with a complex of symptoms similar to chronic bronchitis or asthma. Their clinical presentation may not differ from an acute bronchitis syndrome. Pertussis has a unique clinical presentation with a typical catarrhal phase followed by a whoop/paroxysmal and then convalescent phase, which in total may span over 6 to 8 weeks.

Cystic fibrosis is typically accompanied by steatorrhea, nasal polyps, failure to thrive, and recurrent lower respiratory tract symptoms in association with cough. Primary ciliary dyskinesia encompasses the immotile cilia disorders and Kartagener syndrome (rhinosinusitis, bronchitis, or bronchiectasis and situs inversus). Patients affected with these disorders exhibit a defect in mucociliary transport and present with chronic cough and recurrent lower respiratory disease.