The impact of pertussis in infants. insights from a hospital-based enhanced surveillance system, Lazio region, Italy, 2016 to 2019

Background: Routine surveillance systems for pertussis often suffer from under-recognition and under-reporting. Aim: Our aim was to describe the epidemiology and the clinical features of pertussis in children younger than 1 year in an Italian region, detected through an enhanced hospital surveillance system. Methods: From 2016 to 2019, we monitored the incidence and the clinical characteristics of hospitalised pertussis cases younger than 1 year in two paediatric hospitals involved in the PERTINENT project. Results: We detected 141 pertussis cases, corresponding to an estimated incidence of 105.8 per 100.000 in 2016, 91.7 per 100.000 in 2017, 64.5 per 100.000 in 2018 and 40.9 per 100.000 in 2019, based on the hospitals' catchment area, roughly corresponding to the Lazio region. A total of 101 cases (77.1%) had a household member with cough or other respiratory symptoms. The most frequent combination of symptoms was paroxysmal cough with apnoea in the absence of fever. Almost 40% had been prescribed an antibiotic treatment before hospitalisation, and the median time from symptom onset to contact with the hospital was 8 days. Thirty-one (22.0%) had complications. Conclusion: An enhanced surveillance system showed a high incidence of pertussis among infants in the Lazio region, where the impact of this disease may still be underestimated. Increasing the coverage of pertussis immunisation among pregnant women and improving the capacity for early detection in primary care may contribute to reducing the impact of pertussis among infants.