Epidemiology of pertussis in Italy: disease trends over the last century

Abstract

We reviewed the epidemiology of pertussis in Italy over the last 125 years to identify disease trends and factors that could have influenced these trends. We described mortality rates (1888-2012), case fatality rates (1925-2012), cumulative incidence rates (1925-2013) and age-specific incidence rates (1974-2013). We compared data from routine surveillance with data from a paediatric sentinel surveillance system to estimate under-notification. Pertussis mortality decreased from 42.5 per 100,000 population in 1890 to no reported pertussis-related death after 2002. Incidence decreased from 86.3 per 100,000 in 1927 to 1 per 100,000 after 2008. Vaccine coverage increased from 32.8% in 1993 to about 96% after 2006. As for under-notification, mean sentinel/routine surveillance incidence ratio increased with age (from 1.8 in <1 year-olds to 12.9 in 10-14 year-olds). Pertussis mortality decreased before the introduction of immunisation. Incidence has decreased only after the introduction of pertussis vaccine and in particular after the achievement of a high immunisation coverage with acellular vaccines. Routine surveillance does not show an increase in cumulative incidence nor in ≥ 15 year-olds as reported by other countries. Underrecognition because of atypical presentation and the infrequent use of laboratory tests may be responsible for under-notification, and therefore affect incidence reports and management of immunisation programmes.