Impact of the 13-valent pneumococcal conjugate vaccine (PCV13) on acute mastoiditis in children in southern Israel: A 12-year retrospective comparative study (2005-2016).

Objectives: To define the trends in acute mastoiditis (AM) incidence, microbiology, complications and management in children, before and after the 13-valent pneumococcal conjugate vaccine (PVC13) introduction.
Methods: Medical records of all AM patients <15 years of age diagnosed during 2005-2016 were reviewed. The study years were divided into three periods: pre-vaccination (2005-2008), interim (2009-2011) and post-PCV13 vaccination (2012-2016).
Results: 238 patients (53.4% males) were enrolled, 81, 56 and 101 in the 3 time periods, respectively. Overall, 177/238 (75.2%) of children were <5 years of age. Mean AM incidence in the whole population was 10.32/100,000, with no changes during the study years. Ninety-three (45.6%) of 204 evaluable patients had positive middle ear fluid/mastoid cultures; S. pneumoniae (SP) was isolated in 47/93 (50.5%) cases. Mean incidence of SP-AM during the study years was 2.49 cases/100,000. A trend for decrease in mean incidence of SP-AM was recorded between the pre and the post-vaccination periods (3.05/100,000 vs. 1.82/100,000, P = 0.069). Among patients <5 years, SP-AM rates decreased from pre to post-vaccination period (19/50, 38% vs. 15/73, 20.6%, P = 0.034). No changes were reported in percentages of culture negative-AM and of AM complications in the post-PCV13 period compared with the pre-vaccine period. A significant decrease in distribution of PCV13 serotypes was recorded (17/19, 89.5% vs. 8/12, 66.6% and vs. 7/16, 43.75% during the 3 study periods, P = 0.015) accompanied by a complementary increase in non-vaccine serotypes.
Conclusions: The introduction of PCV13 was accompanied by a significant decrease in SP-AM cases among children <5 years of age. PCV13 serotypes decreased significantly as etiologic agents of SP-AM while non-vaccine serotypes and culture negative-AM became more common in the postvaccination period.
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