Cough is one of the most common symptoms prompting patients to see a doctor in the United States with an estimated 30 million trips to the doctor for this problem each year. More than 40% of the patients seen in our allergy and pulmonary practice between November and February complain of cough.
Cough is classified as acute, sub acute or chronic depending on how long the symptom has been present. Acute cough lasts for less than three weeks and is most commonly the result of an acute respiratory tract infection. Other more serious causes of acute cough include pneumonia and in our clinic in Arizona, coccidiomycosis infection or valley fever.
A cough associated with typical cold symptoms may be called bronchitis, particularly when symptoms last for more than a week. Acute bronchitis is most often caused by a viral infection although other respiratory infections besides viruses, including Mycoplasma pneumoniae, Chlamydophila pneumoniae, and Bordetella pertussis may be involved. Although most viral infections cause symptoms lasting less than 2-3 weeks, some patients with viral or other upper respiratory tract infections will continue to cough for more than eight weeks after the acute infection. This persistent cough may be the result of a type of airway injury. Although the source of the infection is gone, the injury remains and takes time to heal.
Another important cause of acute cough in children in adults is pertussis (whooping cough). Pertussis is a very contagious disease caused by the bacteria Bordetella pertussis. Before the advent of vaccinations in the 1940s, pertussis was a major cause of severe illness and death among infants and children. Although cases of pertussis decreased by more than 99% after the introduction of pertussis vaccine, it remains a cause for concern, in part because of the incomplete protection provided by the vaccine and the increasing numbers of children that are never vaccinated. In fact, pertussis is the only vaccine-preventable disease that is associated with increasing deaths in the United States. In 2010, more than nine thousand cases of whooping cough were reported in California. At least ten infants died from the infection prompting the health authorities to declare a pertusis epidemic.
Pertusis infection usually begins with symptoms similar to the common cold although after several weeks, frequent and often violent coughing begins. The illness is most severe in infants and young children, particularly in those that have not been immunized. In adults, the only symptoms may be a persistent cough.
In a recent study published in The Journal of Allergy and Clinical Immunology (JACI), the risk of adults and children with asthma developing whooping cough was 1.7 times higher than those without asthma, suggesting that asthma significantly increased risk for whooping cough.
A cough lasting more than 4-6 weeks without a clear history of acute respiratory infection is considered chronic and is most likely the result of one of three conditions: asthma, rhinitis/sinusitis and gastroesophageal reflux disease.
Asthma and rhinitis/sinusitis are frequently the result of allergies and so a history of allergies or a positive allergy evaluation strengthens the likelihood that one of these conditions is behind the cough.
Gastroesophageal reflux disease (GERD) and laryngopharyngeal reflux disease (LPR) are conditions associated with the leakage of stomach contents into the esophagus. In GERD, stomach acid refluxes into the lower esophagus causing irritation and damage. Exposed nerves in the esophagus can cause cough as well as pain (heartburn). In LPR, stomach contents may reach to the top of the esophagus causing direct irritation of the throat and possible sinuses. The throat and upper airway are lined with cells that produce mucous as well as cells that have hair-like projections or cilia that sweeps the mucous to the back of the throat where it is swallowed. Acid and protein-destroying enzymes in the refluxed stomach contents inflame and damage the hair cells, hindering the ability to clear mucous. The result is pooling of mucous in the back of the throat and recurrent cough to clear it. It is estimated that 50% of patients with LPR have no other symptom of their condition other than cough and is therefore frequently missed. GERD and LPR should be suspected if an evaluation for allergies, asthma, and sinus disease is negative and the cough fails to respond to conventional treatment.