Isolated night cough in children: how does it differ from wheeze?

Abstract

It has been postulated that some children with recurrent cough but no wheeze have a mild form of asthma (cough variant asthma), with similar risk factors and an increased risk of future wheeze. This longitudinal study compared risk factors for isolated night cough and for wheeze in the Leicester Respiratory Cohort in children aged 1, 4, 6 and 9 years and compared prognosis of children with isolated night cough, children with wheeze and asymptomatic children. We included 4101 children aged 1 year, 2854 aged 4 years, 2369 aged 6 years and 1688 aged 9 years. The prevalence of isolated night cough was 10% at age 1 year and 18% in older children. Prevalence of wheeze decreased from 35% at 1 year to 13% at 9 years. Although several risk factors were similar for cough and wheeze, day care, reflux and family history of bronchitis were more strongly associated with cough, and male sex and family history of asthma with wheeze. Over one-third of preschool children with cough continued to cough at school age, but their risk of developing wheeze was similar to that of children who were asymptomatic at earlier surveys. Wheeze tracked more strongly throughout childhood than cough. In conclusion, our study showed that only some risk factors for cough and wheeze were shared but many were not, and there was little evidence for an increased risk of future wheeze in children with isolated night cough. This provides little support for the hypothesis that recurrent cough without wheeze may indicate a variant form of asthma.

FIGURE 1

Study design: prevalence of wheeze and isolated cough at ages 1, 4, 6 and 9 years, and factors associated with prevalence and prognosis of these symptoms. The size of rectangular boxes represents the respective number of children with cough, wheeze or no symptoms, and the width of the arrows semi-quantitatively demonstrates the likelihood to stay in the same or change to a different group at subsequent surveys.

FIGURE 2

Risk factors for prevalent isolated night cough and wheeze at age 4 years (n=2854). Association of different factors with cough and with wheeze, compared to asymptomatic children, in a fully adjusted model (adjusted for all covariates with p-values <0.1 for either cough or wheeze in univariable models), presented as relative risk ratio estimates with confidence intervals. Cough was defined as night cough without wheeze.

FIGURE 3

Risk factors for prevalent isolated night cough and wheeze at age 6 years (n=2369). Association of different factors with cough and with wheeze, compared to asymptomatic children, in a fully adjusted model (adjusted for all covariates with p-values <0.1 for either cough or wheeze in univariable models), presented as relative risk ratio estimates with confidence intervals. Cough was defined as night cough without wheeze.

FIGURE 4

Risk factors for prevalent isolated night cough and wheeze at age 9 years (n=1688). Association of different factors with cough and with wheeze, compared to asymptomatic children, in a fully adjusted model (adjusted for all covariates with p-values <0.1 for either cough or wheeze in univariable models), presented as relative risk ratio estimates with confidence intervals. Cough was defined as night cough without wheeze.

FIGURE 5

Prognosis and tracking of respiratory symptoms in children. Proportion of children with wheeze, isolated night cough or none of the symptoms, who have wheeze, cough or are asymptomatic 2–3 years later. This figure shows prognosis for three different development periods in childhood (1 to 4 years, 4 to 6 years and 6 to 9 years).