How common is whopping cough?

We organized a nationwide cohort study to measure age-specific pertussis incidence. We followed a representative population served by 78 randomly selected general practitioners. The overall follow-up time was almost 200,000 person-years. We recruited persons who attended participating GPs with symptoms of prolonged cough, interviewed using standardized forms and took nasopharyngeal samples. During the follow up time, GPs consulted 3,864 patients with cough, of which 1,232 were recruited and tested for pertussis and parapertussis. We confirmed 288 pertussis cases (adjusted incidence rate 201 cases per 100,000 person-years) and 78 parapertussis cases (unadjusted incidence rate 39/100,000 person-years). This was one of the largest observational studies carried out by the National Institute of Public Health in Poland, with a considerable budget, excellent coordination team and well performing study sites.