Whooping cough in school age children with persistent cough: prospective cohort study in primary care.

OBJECTIVE: To estimate the proportion of school age children with a persistent cough who have evidence of a recent Bordetella pertussis infection. DESIGN: Prospective cohort study (October 2001 to March 2005). SETTING: General practices in Oxfordshire, England. PARTICIPANTS: 172 children aged 5-16 years who presented to their general practitioner with a cough lasting 14 days or more who consented to have a blood test. MAIN OUTCOME MEASURES: Serological evidence of a recent Bordetella pertussis infection; symptoms at presentation; duration and severity of cough; sleep disturbance (parents and child). RESULTS: 64 (37.2%, 95% confidence interval 30.0% to 44.4%) children had serological evidence of a recent Bordetella pertussis infection; 55 (85.9%) of these children had been fully immunised. At presentation, children with whooping cough were more likely than others to have whooping (odds ratio 2.85, 95% confidence interval 1.39 to 5.82), vomiting (4.35, 2.04 to 9.25), and sputum production (2.39, 1.14 to 5.02). Children with whooping cough were also more likely to still be coughing two months after the start of their illness (85% v 48%; P = 0.001), continue to have more than five coughing episodes a day (P = 0.049), and cause sleep disturbance for their parents (P = 0.003). CONCLUSIONS: For school age children presenting to primary care with a cough lasting two weeks or more, a diagnosis of whooping cough should be considered even if the child has been immunised. Making a secure diagnosis of whooping cough may prevent inappropriate investigations and treatment.