Evidence of increased circulation of Bordetella pertussis in the Italian adult population from seroprevalence data (2012-2013).

Incidence data on pertussis cases in Italy do not show pertussis resurgence, as recently described in other European countries. The aim of this study was to determine the seroprevalence of IgG antibodies to pertussis toxin (PT-IgG) in selected adult age groups, which can serve as a reservoir of B. pertussis and be responsible for onward transmission to vulnerable infants. The seroprevalence of PT-IgG was studied in sera collected in 2012-13 in age groups 20-29, 30-39 (reproductive age), and ≥ 60 years. These data were compared with those from sera collected in similar age groups in 1996-97. More than 80 % of the adult population analysed in the 2012-13 presented detectable levels of PT-IgG (> 5 IU ml-1 ). The PT-IgG titres 50 – 99 IU ml-1 indicatives of infections in the last few years, and PT-IgG titres ≥ 100 IU ml-1 in the last year, reached 9.1 % (95 % CI 6.9 – 11.3 %; 58/639) and 5 % (95 % CI 3.3 – 6.7 %; 32/639) seroprevalence, respectively. Notably, the proportion of subjects with seroprevalence indicative of recent infections increased significantly from 9.3 % (95 % CI 7.5 – 11.1 %; 96/1037) in 1996-97 to 14.1 % (95 % CI 11.4 – 16.8 %, 90/639), in 2012-13. Overall our data clearly indicate a significant increase in the circulation of B. pertussis in adults in Italy and therefore it is likely that statutory notification system underestimates the real incidence of the disease. These findings have implications for preventive strategies.

Authors:Palazzo R1, Carollo M2, Fedele G3, Rizzo C4, Rota MC5, Giammanco A6, Iannazzo S7, Ausiello CM8
Journal:J Med Microbiol. 2016