The Cough Conundrum: is this Whooping Cough? A study of acute persistent cough in school age children and adults in primary care in Auckland

Abstract

Aims New Zealand has a high burden of whooping cough (pertussis) disease. Pertussis can be difficult to diagnose in school age children and adults in whom it is largely a vaccine-modified illness. New clinical information or diagnostic tools which help to differentiate pertussis from other cough illnesses in primary care would be of value to practitioners. The aims of this study were: (i) to estimate the proportion of people aged 5 to 49 years identified in primary care with an acute persistent cough that have evidence of recent Bordetella pertussis (B. pertussis) infection; and (ii) to describe the symptoms at enrolment of study participants who have recent infection with B. pertussis, and those who do not. Method Study participants aged 5-49 years were enrolled through active surveillance of acute persistent cough of two weeks duration or greater at recruited primary care practices in Auckland, New Zealand from May to October 2011. Data collected comprised a participant questionnaire, an oral fluid sample and self-completed cough checklists. Recent B. pertussis infection was determined by measurement of immunoglobulin G (IgG) antibodies to pertussis toxin (PT) in the oral fluid sample. An IgG antibody titre to PT of ≥70 arbitrary units defined recent infection. Analyses of cough duration (Cox proportional hazards survival analysis) and symptoms at enrolment (logistic regression and Search Partition Analysis) were performed. Results Fifteen referring general practices were recruited. Two hundred and twenty six participants were enrolled of whom 70 (31%) were children (5-16 years) and 156 (69%) were adults (17-49 years). Oral fluid samples were obtained from 225 participants. Ten percent (23/222) of participants had evidence of recent B. pertussis infection including a larger proportion of children than adults (17% vs. 7%, p=0.003). Neither cough duration, nor any individual symptoms at enrolment, discriminated between those with, and those without, recent B. pertussis infection. Conclusion Pertussis is a frequent cause of acute persistent cough identified in primary care. Clinical differentiation of pertussis from other causes of acute persistent cough is difficult. The oral fluid based assay is a non-invasive diagnostic test that would be of high utility in primary care.