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1 March 2009

Dear Editor,

PROTRACTED COUGH: PROBLEMS AND OPPORTUNITIES

Chronic cough in children has long troubled parents and doctors. In their paper, Dr Petsky and her co-workers1 have isolated a specific group within the overall syndrome, labelled it ‘protracted cough’, and have shown that when these children have an acute respiratory illness, the cough lasts longer than in normal children or children with proven asthma. This paper advances our knowledge, but does not answer many of the problems of diagnosis, epidemiology, management and prognosis that we face in routine clinical practice.

The authors define the condition by its clinical features plus the findings on bronchial lavage. This procedure can be carried out only in respiratory units in tertiary level hospitals, so those working ‘in the field’ cannot diagnose the condition. We therefore cannot know the overall prevalence of ‘protracted cough’ nor factor it into our clinical diagnoses. There are two ways around this problem. The authors might devise an algorithm for making a reasonably certain diagnosis of ‘protracted cough’ based on clinical evidence plus or minus routine laboratory tests. The second possibility is to use the nasal mucosa as a surrogate for the bronchial mucosa. They are both part of the respiratory epithelium, and they often show similar changes in disease.2 It is easy to take a swab from the nose, plate it on to a microscope slide and/or make a culture. The cell types, for example, the eosinophil/neutrophil ratio, and a bacterial culture probably reflect events in the bronchi. These or other simple tests could make the diagnosis widely available.

The authors report that children with ‘protracted cough’ have a longer illness than other children, but make no suggestions for management, or indicate whether appropriate treatment can alter the duration of the illness. Studies over many years have shown that antibiotics do not shorten the course of acute respiratory infections,3 but these overall results may hide outcomes for specific subgroups. If the main underlying problem in these children is inefficient response to infection, then starting antibiotics early might shorten the illness. I can find no published evidence for or against this line of action. Would long-term antibiotics compensate for the inefficient immune response?

The third concern is the long-term prognosis for ‘protracted cough’. Does it lead to adult lung disease? Is the poor response to infections localised to the bronchi or is the response to infection elsewhere also compromised? Does the child's immune response improve with age? And finally, can we modify the long-term outcome with suitable management?

Chronic cough in children is not life threatening, but it is widespread and troublesome. By identifying a subgroup within the overall syndrome, the authors have made us think again about diagnosis and management, and may have made a major breakthrough. However, for this to be useful, the diagnosis must be taken out of the specialised laboratory and made available to routine clinical practice. Only then can we establish the epidemiology, best methods of management and the prognosis.

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