Cough symptoms in children aged 5-14 years in Sydney, Australia: non-specific cough or unrecognized pertussis?

Objective: The aim of this study was to estimate the community prevalence of coughing symptoms, consistent with surveillance definitions for pertussis, and doctor-diagnosed pertussis in children aged 5-14 years. Methodology: A telephone survey of a cross-sectional community sample of parents regarding their child's cough symptoms in the previous 12 months was undertaken in a representative Australian urban region. Results: In 2020 interviews, parents reported that 22% of children had a cough lasting 2 weeks or longer in the preceding 12 months, and 14% (283) had additional symptoms meeting the Centers for Disease Control (CDC) case definition for pertussis. A cough meeting the case definition was significantly more commonly reported by parents of children aged 5-9 years (17%; P < 0.001) but reported exposure to diagnosed pertussis in such cases was significantly more common in children aged 1014 years (4.3%; odds ratio 12.8; P < 0.01). Parents of 90% of children meeting: the CDC case definition sought medical advice. A diagnosis of pertussis was reported in only 1.2% of cases, which extrapolates to an annual incidence of doctor-diagnosed pertussis of 347/100 000 (95% confidence interval, 140-714 per 100 000). This contrasts with 29/100 000 notified cases in the same age group, time period and geographic area. Conclusion: Cough episodes meeting a clinical case definition for pertussis commonly used in surveillance are reported by a high proportion of carers of school-aged children in Australia. The majority of children who met the CDC and Australian case definitions for pertussis and sought medical attention were not identified as potentially having pertussis, suggesting underdiagnosis of pertussis. Even if less than half of this is true pertussis, the potential impact in terms of transmission of pertussis in the community is likely to be high. The reported incidence of doctor-diagnosed disease estimated from this survey was at least five and up to 20 times the official notification rate. More work needs to be done in raising awareness among medical practitioners of pertussis as a differential diagnosis in older children and adolescents with cough.