Once it has been established that the cough is indeed persistent for more than 3 weeks, characteristics of the cough may be noted. A cough productive of purulent sputum usually indicates an infectious cause from a bacterial or viral source. A productive cough usually occurs in children only after the age of 4 or 5 years old. A productive cough at a younger age should raise the examiner's index of suspicion for cystic fibrosis in the toddler age group of tracheoesophageal fistula or gastroesophageal reflux in infants. Viral infections tend to be recurrent. Bacteria that cause chronic cough include Chlamydia, Mycoplasma, Bordatella pertussis, and Mycobacterium tuberculosis. A cough producing thick, tenacious sputum may be associated with cystic fibrosis. A dry, brassy, or stridorous cough may be associated with upper airway disease caused by foreign body aspiration, laryngitis, or laryngotracheobronchitis (croup). Paroxysms of cough are found in pertussis, cystic fibrosis, and foreign body aspiration. A paroxysm of cough followed by a whoop is the classic presentation of whooping cough caused by B. pertussis. The whoop rarely is seen in infants. A productive throat clearing indicates a postnasal drip associated with sinusitis. The staccato cough is associated with chlamydia pneumonia. A psychogenic cough that usually presents as dry and brassy may be bizarre, with a honking or barking quality. A cough associated with a wheeze is likely caused by asthma (Table 1) 
Timing of the cough also carries certain implications. Cough that occurs with feeding implies aspiration and possibly a congenital abnormality. Reflux and overfeeding would be the more common cause in the infant, whereas tracheoesophageal fistula or laryngeal cleft are uncommon. A child who just enters daycare likely will experience an increased frequency of URIs, whereas seasonal variations may indicate an allergic cause. A temporal relationship to an irritant such as smoke or an allergen such as a pet may be established. Nighttime cough may signal reactive airway disease or sinusitis with recumbent postnasal drip. Cough that disappears with sleep should raise concern of a psychogenic cause. Cough that is worse on awakening may imply cystic fibrosis or bronchiectasis. Cough associated with exercise may be caused by exercise-induced asthma, cystic fibrosis, and bronchiectasis and rarely may suggest heart disease or extrinsic airway compression.
An associated symptom such as hemoptysis raises the concern about such diseases as pulmonary tuberculosis, cystic fibrosis, bronchiectasis, or possibly foreign body aspiration. Headache, malodorous breath, and nasal discharge may signify a chronic sinusitis. Prolonged fever associated with weight loss indicates a more serious cause such as HIV infection.
Persistent fever
Failure to grow or gain weight
Clubbing
Purulent sputum
Hypoxemia
Refractory chest radiographic infiltrates
Hemoptysis
The critical element of the physical examination is the general clinical impression. Does this child appear healthy, ill, or toxic? The signs and symptoms of serious disease should be considered early in the evaluation:  
With a URI, the child will appear mildly ill and have no significant fever. Rhinorrhea and pharyngeal erythema may be present, but the examination otherwise should be benign. In a child with reactive airway disease, URI symptoms may be present in addition to audibly harsh respirations, a prolonged expiratory phase, and wheeze. Musical rales may be present. A barrel chest suggests a chronic problem. The liver and spleen may be palpable because of hyperinflation of the lungs. Nasal polyps are suggestive of atopy.
Sinusitis in children is estimated to be a complicating factor in 5% to 10% of all URIs. Because children average six to eight colds per year, sinusitis is a common condition in primary care. Sinusitis typically presents with a nasal discharge of any quality (thin to thick and clear to purulent). The cough usually is present by day but is usually worse at night. Halitosis (bad breath) may be present. Facial pain and headache are useful indicators only after the age of about 10 to 12. Painless morning eye swelling may be noted by the parent in the school-aged population. Fever, if present, is usually low grade. 
The infant with tracheoesophageal fistula often will have early respiratory distress, cyanosis, excessive secretions in the oropharynx, and cough with feeding. Splinting may be seen as well. Tracheobronchial compression by anomalous or enlarged vessels causes an infant to have noisy breathing and a cough. The infant may attempt to optimize the airway by assuming an opisthotonos position.
Children between the ages of 6 months to 4 years are at particular risk of aspiration of foreign bodies. The initial response is usually gagging, coughing, and wheezing. If the foreign body has been allowed to remain, however, distal obstruction, mucous production, and inflammation may obstruct the airway, causingatelectasis or an infiltrate. Decreased breath sounds over the affected lung with inspiratory rhonchi and expiratory wheezing are found.
Inspection for stigmata of allergic disease will reveal a pale, boggy nasal mucosa, clear rhinorrhea, allergic shiners, and the nasal crease.
Chronic illness presents with generalized signs such as poor weight gain. Scattered diminished breath sounds, cyanosis, and digital clubbing are late signs of cystic fibrosis.
Tobacco abuse may be identified by the smell of tobacco or by nicotine stains, whereas sniffing glue and other substances may produce a clouded sensorium.