title: Negative pressure tympanograms in children less than 2 years of age--different bacterial findings in otitis media by tympanometric results.
abstract: OBJECTIVE
  The interpretation of negative pressure tympanograms as indicators of the presence of middle ear fluid has been ambiguous. Our purpose was to assess the occurrence and implications of negative pressure tympanograms and to study their association with bacterial pathogens in otitis media.
  
  
  METHODS
  Altogether 329 infants were enrolled at a well-baby clinic for the Finnish Otitis Media Cohort Study, a longitudinal prospective cohort study. The children were closely followed in a special study clinic from 2 to 24 months of age for respiratory diseases, especially acute otitis media. Children were examined at the study clinic with tympanometry and pneumatic otoscopy whenever visiting the study clinic for respiratory disease. Myringotomy with aspiration was performed if middle ear fluid was suspected in otoscopy. Occurrence of middle ear fluid in ears with negative pressure tympanograms (less than -100 daPa) was assessed. Nested case control design matched by visit type (acute or follow-up visit) and month of visit was used for analysis of association of bacterial pathogens and tympanometric results.
  
  
  RESULTS
  Middle ear fluid was encountered in 15% of ears with negative tympanometric peak pressure, a lower proportion than described previously. In otitis media with a negative tympanometric peak pressure, 71% of bacterial cultures remained negative for the main pathogens, compared to 36% in matched controls (P<0.001). Especially Streptococcus pneumoniae but also Haemophilus influenzae were rarely found in samples from negative pressure ears. Moraxella catarrhalis was equally often found.
  
  
  CONCLUSIONS
  Negative pressure tympanogram is a poor indicator for the presence of middle ear fluid. Furthermore, if otitis media is diagnosed with negative tympanometric peak pressure negative middle ear bacterial culture for the main pathogens is highly probable. Expectant follow-up might be more appropriate than routine antibiotic treatment.
authors.affiliation: National Public Health Institute, Helsinki, Finland. aapalmu@tays.fi
authors.forename: A
authors.initials: A
authors.lastname: Palmu
authors.forename: R
authors.initials: R
authors.lastname: Syrjänen
authors.forename: T
authors.initials: T
authors.lastname: Kilpi
authors.forename: H
authors.initials: H
authors.lastname: Pursiainen
authors.forename: H
authors.initials: H
authors.lastname: Puhakka
authors.forename: T
authors.initials: T
authors.lastname: Rahko
authors.forename: E
authors.initials: E
authors.lastname: Herva
authors.forename: A
authors.initials: A
authors.lastname: Takala
mesh_terms: D000158:Acoustic Impedance Tests; D000208:Acute Disease; D005387:Finland; D006193:Haemophilus influenzae / Q000302:isolation & purification; D006320:Hearing Tests; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D001936:Moraxella catarrhalis / Q000302:isolation & purification; D015999:Multivariate Analysis; D010034:Otitis Media with Effusion / Q000175:diagnosis / Q000382:microbiology*; D011312:Pressure; D011446:Prospective Studies; D018709:Statistics, Nonparametric; D013296:Streptococcus pneumoniae / Q000302:isolation & purification