Whooping cough in school age children presenting with persistent cough in UK primary care after introduction of the preschool pertussis booster vaccination: prospective cohort study

Abstract

Objective: To estimate the prevalence and clinical severity of whooping cough (pertussis) in school age children presenting with persistent cough in primary care since the introduction and implementation of the preschool pertussis booster vaccination.

Design: Prospective cohort study (November 2010 to December 2012).

Setting: General practices in Thames Valley, UK.

Participants: 279 children aged 5 to 15 years who presented in primary care with a persistent cough of two to eight weeks' duration. Exclusion criteria were cough likely to be caused by a serious underlying medical condition, known immunodeficiency or immunocompromise, participation in another clinical research study, and preschool pertussis booster vaccination received less than one year previously.

Main outcome measures: Evidence of recent pertussis infection based on an oral fluid anti-pertussis toxin IgG titre of at least 70 arbitrary units. Cough frequency was measured in six children with laboratory confirmed pertussis.

Results: 56 (20%, 95% confidence interval 16% to 25%) children had evidence of recent pertussis infection, including 39 (18%, 13% to 24%) of 215 children who had been fully vaccinated. The risk of pertussis was more than three times higher (21/53; 40%, 26% to 54%) in children who had received the preschool pertussis booster vaccination seven years or more previously than in those who had received it less than seven years previously (20/171; 12%, 7% to 17%). The risk of pertussis was similar between children who received five and three component preschool pertussis booster vaccines (risk ratio for five component vaccine 1.14, 0.64 to 2.03). Four of six children in whom cough frequency was measured coughed more than 400 times in 24 hours.

Conclusions: Pertussis can still be found in a fifth of school age children who present in primary care with persistent cough and can cause clinically significant cough in fully vaccinated children. These findings will help to inform consideration of the need for an adolescent pertussis booster vaccination in the United Kingdom.

Study registration: UK Clinical Research Network portfolio ID 8361.

Fig 1 Age distribution of laboratory confirmed pertussis cases. aU=arbitrary units; IgG-PT=oral fluid anti-pertussis toxin IgG titre. Laboratory confirmed pertussis was diagnosed in children with positive IgG-PT titre (≥70 aU). *Children born before October 1997 are unlikely to have been offered the preschool pertussis booster vaccination, as this was introduced only in October 2001

Fig 2 Percentage of children aged 5 to 15 years with laboratory confirmed pertussis per quarter (2011 to 2012), with 95% confidence intervals. Study cohort (Thames Valley): laboratory confirmed pertussis diagnosed by oral fluid anti-pertussis toxin IgG titre ≥70 arbitrary units; percentage of children with laboratory confirmed pertussis calculated on basis of all oral fluid samples containing sufficient total IgG for analysis. England and Wales: laboratory confirmed pertussis diagnosed by serology; percentage of children with laboratory confirmed pertussis calculated on basis of all samples submitted to Public Health England (formerly Health Protection Agency) for analysis

Fig 3 Laboratory confirmed pertussis in children presenting with persistent cough in primary care after receiving preschool pertussis booster vaccination (n=224). Error bars represent 95% confidence intervals

Fig 4 24 hour cough frequency in children with laboratory confirmed pertussis (n=6). Daytime cough monitoring period was from 0800 to 2200. All six participants received complete primary pertussis vaccinations and preschool pertussis booster vaccination