title: High incidence of septic shock caused by Streptococcus pneumoniae serotype 3--a retrospective epidemiological study.
abstract: BACKGROUND
  More than 90 immunologically distinct serotypes of Streptococcus pneumoniae exist, and it is not fully elucidated whether the serotype is a risk factor for severity of invasive pneumococcal disease (IPD). Our hypothesis is that serotypes differ in their capacity to cause septic shock.
  
  
  METHODS
  We performed a retrospective study in Southern Sweden based upon 513 patients with IPD in the pre-vaccine era 2006-2008. The serotype, co-morbidity, and sepsis severity were determined. Serotypes were compared to serotype 14 as a reference and grouped according to their invasive potential, that is, high (serogroups 1, 5 and 7), intermediate (serogroups 4, 9, 14 and 18) and, finally, low invasive potential (serogroups 3, 6, 8, 15, 19, 23 and 33).
  
  
  RESULTS
  Patients with S. pneumoniae serotype 3 had significantly more often septic shock (25%, odds ratio (OR) 6.33 [95% confidence interval (CI) 1.59-25.29]), higher mortality (30%, OR 2.86 [CI 1.02-8.00]), and more often co-morbidities (83%, OR 3.82 [CI 1.39-10.54]) when compared to serotype 14. A significant difference in age and co-morbidities (p ≤ 0.001) was found when patient data were pooled according to the invasive potential of the infecting pneumococci. The median age and percentage of patients with underlying co-morbidities were 72 years and 79%, respectively, for serogroups associated with low invasiveness, 68 years and 61%, respectively, for serogroups with intermediate invasiveness, and, finally, 62 years and 48%, respectively, for serogroups with high invasiveness. No difference in sepsis severity was found between the three groups.
  
  
  CONCLUSIONS
  S. pneumoniae serotype 3 more often caused septic shock compared to serotype 14. Our results support the hypothesis that serotypes with high invasiveness mainly cause IPD in younger patients with less co-morbidities. In contrast, serogroups with low and intermediate invasive potential mostly cause IPD in the elderly with defined co-morbidities, and thus can be considered as opportunistic.
authors.affiliation: Department of Laboratory Medicine Malmö, Medical microbiology, SE-205 02 Malmö, Sweden. jonas.ahl@med.lu.se.
authors.forename: Jonas
authors.initials: J
authors.lastname: Ahl
authors.forename: Nils
authors.initials: N
authors.lastname: Littorin
authors.forename: Arne
authors.initials: A
authors.lastname: Forsgren
authors.forename: Inga
authors.initials: I
authors.lastname: Odenholt
authors.forename: Fredrik
authors.initials: F
authors.lastname: Resman
authors.forename: Kristian
authors.initials: K
authors.lastname: Riesbeck
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D011008:Pneumococcal Infections / Q000453:epidemiology* / Q000382:microbiology*; D012189:Retrospective Studies; D012307:Risk Factors; D012703:Serotyping; D012772:Shock, Septic / Q000453:epidemiology* / Q000382:microbiology*; D013296:Streptococcus pneumoniae / Q000145:classification / Q000302:isolation & purification*; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult