Related Experiment Videos
Cumulative incidence of pertussis in an unvaccinated preschool cohort based on notifications, interview and serology
1Division of Child Health, Landstingets kansli, Jönköping, Sweden.
Insights
Pertussis (whooping cough) incidence is underestimated by surveillance systems. Serological testing revealed significantly higher pertussis rates than reported by Child Health Centres in unvaccinated children.
Area of Science:
- Epidemiology
- Immunology
- Public Health
Background:
- Cessation of pertussis immunisation in Sweden led to the study of unvaccinated cohorts.
- Accurate incidence data is crucial for understanding disease dynamics and vaccine impact.
Purpose of the Study:
- To investigate the cumulative incidence of pertussis up to six years of age in unvaccinated children.
- To validate the national epidemiological surveillance system against serological findings.
Main Methods:
- Serological testing and parental interviews were conducted on an unvaccinated cohort.
- Data from Child Health Centres (CHCs) epidemiological surveillance system was compared with serological results.
Main Results:
- Serological assays indicated a pertussis incidence of 54%, significantly higher than the 31% reported by CHCs.
- The CHC surveillance system demonstrated high specificity (93%) but low sensitivity (52%).
- A substantial proportion of children with severe coughs, not initially suspected as pertussis, were seropositive.
Conclusions:
- The national epidemiological surveillance system underestimates pertussis incidence, even when yielding the highest reported rates.
- Serological methods provide a more accurate assessment of pertussis prevalence in unvaccinated populations.
- Improved surveillance strategies are needed to capture the true burden of pertussis.
Abstract:
The cumulative incidence of pertussis at six years of age in the first unvaccinated cohort after cessation of immunisation in Sweden was investigated by serological methods and by a validation of the national epidemiological surveillance system by reports from the Child Health Centres (CHCs). In 312/385 (81%) eligible children, both an interview with the parents and a blood sample from the child could be obtained. The CHC reports yielded a cumulative incidence of 31%, whereas the serological assays found 54%. Of the cases reported by the parents to the CHCs, 89% were seropositives. In the additional cases of pertussis reported at the study interview, only 61% could be confirmed (p less than 0.001). Among children with reported severe cough not suspected to be pertussis, 46% were seropositive, distributed as 33% seropositives in cases with cough duration of less than 4 weeks and 69% for longer coughs (p less than 0.01). In the CHC reports, the parental diagnosis was found to have been confirmed in three-quarters of cases by medical personnel. The CHC reporting system was thus found to be reliable with an observed specificity of 93%, but sensitivity of only 52%. Thus, even this surveillance system, which yields the highest incidence rates, underestimates the incidence of the disease.