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In the 1930s, when cystic fibrosis (CF) was first described, most affected children died in the first few years of life. Over the past decades survival of CF patients has increased, mainly as a result of aggressive antibiotic policies and improved nutrition. Chronic colonisation of the respiratory tract with bacterial pathogens such as Pseudomonas aeruginosa is strongly associated with progression of pulmonary disease. 1, 2 Thus accurate identification of lower respiratory tract pathogens is of utmost importance in the clinical management of CF. 2a
Expectorated sputum specimens are a reliable source for identification of lower airway bacteria, but very few children aged less than 10 years can expectorate effectively. Bronchoalveolar lavage (BAL) may be superior, 1, 3 but the risk and cost of repeated bronchoscopy and BAL procedures in infants must be taken into consideration when recommending these procedures for routine screening purposes. Cough swabs have been used in these patients as a substitute source for isolating bacterial pathogens. However, studies have shown that although cough swabs have a high positive predictive value, a negative cough swab does not rule out the presence of pathogenic microorganisms in the lower airways of patients with CF. 4
The aim of this study was to look at the cough plate as an alternative method of obtaining samples in CF patients. Historically cough plates were used in diagnosis of whooping cough but have been superseded by the use of per nasal swab. 5, 6 In order to determine the diagnostic accuracy of the cough plate we compared cough plates with dry cough swabs, moistened cough swabs, and spontaneously expectorated sputum samples in CF patients attending the outpatient clinic, using sputum as the "gold standard".
METHODS
A randomised, prospective study of respiratory sample collection was conducted between April and December 2001 in CF patients aged between 8 and 16 years, expectorating sputum and attending the tertiary CF clinic at Birmingham Children's Hospital.
Four different specimens (sputum, cough plate (CP; 5% horse blood agar), dry swab (DS), and moistened cough swab (MS)) were collected from each patient. It was felt that moistening swabs with sterile saline might enhance microbial adherence to or survival on swabs. Thirty one patients in all who could produce sputum were included in the study. Patients were...