title: Temporal trends in invasive pneumococcal disease and pneumococcal serotypes over 7 decades.
abstract: BACKGROUND
  Pneumococcal infections have historically played a major role in terms of morbidity and mortality. We explored historical trends of invasive pneumococcal disease (IPD) and pneumococcal serotypes in a population exposed to limited antibiotic selective pressure and conjugate pneumococcal vaccination (PCV).
  
  
  METHODS
  Retrospective cohort study based on nationwide laboratory surveillance data on IPD collected uninterruptedly in Denmark during 1938-2007. Changes in the reported incidence and trends of pneumococcal serotypes were explored using nonlinear regression analysis.
  
  
  RESULTS
  There were 25,502 IPD cases included in our study. The median incidence of IPD increased from 2.8 cases per 100,000 population (interquartile range [IQR], 1.5-2.6) during the first 4 decades to 15.7 cases per 100,000 population (IQR, 7-20.4) during the 1980s and 1990s, mainly attributed to an increase in the number of bacteremia cases. The incidence of meningitis remained relatively stable, with a median of 1.3 cases per 100,000 population (IQR, 0.9-1.6). The proportions of serotypes/groups 4 and 9 increased; the proportion of serotype 18C decreased; the proportions of serotypes 6, 7F, 14, and 23F remained stable; and serotype 2 nearly disappeared. Before the 1960s, serotypes 1, 2, 3, and 5 presented peaks every 2-3 years, becoming less frequent during the 1970s with peaks every 7-10 years. Between 20% and 90% of IPD in children <5 years were caused by PCV serotypes during the last 4 decades. Cases of IPD caused by serotype 19A increased before introduction of PCV. Between 1993 and 2007, the level of resistance to macrolides and beta-lactams was 6%.
  
  
  CONCLUSIONS
  The epidemiology of IPD and single serotypes has constantly changed over the past 7 decades. PCV serotypes appeared to dominate the pneumococcal population.
authors.affiliation: National Neisseria and Streptococcus Reference Center, Department of Bacteriology, Mycology, and Parasitology, Statens Serum Institut, Copenhagen, Denmark. zit@ssi.dk
authors.forename: Zitta B
authors.initials: ZB
authors.lastname: Harboe
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Benfield
authors.forename: Palle
authors.initials: P
authors.lastname: Valentiner-Branth
authors.forename: Thomas
authors.initials: T
authors.lastname: Hjuler
authors.forename: Lotte
authors.initials: L
authors.lastname: Lambertsen
authors.forename: Margit
authors.initials: M
authors.lastname: Kaltoft
authors.forename: Karen
authors.initials: K
authors.lastname: Krogfelt
authors.forename: Hans Christian
authors.initials: HC
authors.lastname: Slotved
authors.forename: Jens Jørgen
authors.initials: JJ
authors.lastname: Christensen
authors.forename: Helle B
authors.initials: HB
authors.lastname: Konradsen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D049673:History, 20th Century; D049674:History, 21st Century; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D011008:Pneumococcal Infections / Q000453:epidemiology* / Q000266:history / Q000382:microbiology*; D012189:Retrospective Studies; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000302:isolation & purification; D055815:Young Adult