Could that Persistent Cough Be Pertussis? Don't Rely on the Whoop
Abstract & Commentary
By Joseph E. Scherger, MD, MPH
Clinical Professor, University of California, San Diego. Dr. Scherger reports no financial relationship to this field of study.
Synopsis: A systematic review shows that the three classical symptoms of paroxysmal cough, post-tussive emesis, and inspiratory whoop are helpful for the diagnosis, but cannot be relied upon to rule in or rule out pertussis as the cause of a chronic cough.
Source: Cornia PB, et al. Does this coughing adolescent or adult patient have pertussis? JAMA 210;304:890-896.
Pertussis continues as a major cause of respiratory infection in the United States among children and adults. Pertussis should be considered in any patient with a persistent and prominent cough. The natural history of the infection has three phases. After a 7- to 10-day incubation period, the catarrhal phase is much like a common cold and lasts 1-2 weeks. The presence of mild cough early may make the clinician suspicious for pertussis. Two early symptoms that may be clinically useful are excessive lacrimation and conjunctival injection.
The paroxysmal phase begins during the second week of the illness and the hallmark symptom is coughing spells. A paroxysm is a series of coughs during a single expiration. The cough paroxysm causes low lung volumes, leading to a vigorous inspiration that may result in a whoop, particularly in infants and children who have a smaller trachea. Other classic symptoms that may be present are post-tussive emesis or syncope. The paroxysmal phase may last for 2-3 months.
The final phase of the illness is a persistent cough that becomes progressively milder. The Chinese name for pertussis is "the 100 day cough." Sputum production is not a hallmark of pertussis, so the presentation may be very similar to a viral bronchitis or pneumonia.
Bordetella pertussis is a gram-negative coccobacillus and is readily transmitted in respiratory secretions. Diagnosis is not easy and is most commonly made from a culture or direct staining of a properly obtained nasopharyngeal specimen. Specimens must be collected from the ciliated respiratory epithelium of the posterior nasopharynx and not the anterior nares or throat. Serum antibody testing is also done, but is not generally useful with the management of an acute infection.
Macrolide antibiotics such as erythromycin, azithromycin, and clarithromycin are the treatment of choice. Trimethoprim-sulfamethoxazole is an alternative for patients unable to tolerate a macrolide. Early treatment may reduce the severity and duration of the illness, but treatment after the first 1-2 weeks may not have a clinical impact. A principal benefit of treatment is to reduce the contagious period that can last 1 month or longer.
Besides giving an excellent clinical review of pertussis, the study group from the University of Washington and the University of California, San Francisco, did a systematic review of the literature to explore the utility of the classic symptoms. They identified five prospective studies as useful. They found that the presence of post-tussive emesis or inspiratory whoop increases the likelihood of pertussis by about two times. The absence of paroxysmal cough or post-tussive emesis decreased the likelihood of pertussis by about two times. Calculating the sensitivity and specificity of the classic symptoms shows that paroxysmal cough is present in close to 100% of patients with pertussis, but is only about 25%-30% specific. Inspiratory whoop is present in 26%-50% of patients with pertussis and is about 75% specific. Post-tussive emesis is present in 33%-70% of patients with pertussis and is about 70% specific.
The differential diagnosis of chronic cough is a major challenge in primary care. Besides a lower respiratory infection, conditions such as asthma and GERD must be considered. Careful history can usually help us sort out the patients with a respiratory infection. The next challenge is sorting out which infections are likely viral and which are bacterial in origin. Without colored sputum as a prominent symptom, "atypical" bacteria such as Chlamydia pneumoniae and Mycoplasma pneumoniae are also considered. We need to add pertussis to the list of common possibilities. Fortunately, all respond to macrolide antibiotics, and all three usually resolve eventually without treatment in generally healthy persons.
What do I use to guide whether I am going to use an antibiotic in the presence of a persistent and paroxysmal cough? The severity of the cough and the presence of physical findings will tip me to using an antibiotic. I tell every patient that the illness could be viral, and that the treatment may have no impact on the recovery from the illness, and that they will recover or I want to hear from them. I find on-line communication with patients to be useful to monitor the course and recovery from these common infections.
This article provides a wonderful clinical update on pertussis and useful clinical research information for diagnosis. Immunization remains the most important public health intervention and we must remember how lethal pertussis can be, especially to infants and young children.