A number of viruses and bacteria are established pathogens in acute otitis media (AOM). Some of these organisms have reported associations with different clinical signs and symptoms. Palmu and colleagues from the Finnish Otitis Media Vaccine Trial examined the correlation between certain clinical findings and bacterial culture results in cases of AOM.
This trial enrolled more than one half of all the available two-month-old children in the study area and followed them prospectively for two years. Children were examined routinely at eight visits over the study period, and parents were asked to bring their child in for examination if they suspected ear or respiratory infection. Ninety-six percent of enrolled children finished the two-year study. Otoscopic examination including insufflation and tympanometry was used to assess for the presence of middle ear fluid. If fluid was apparent, myringotomy was performed, and the fluid was sent for culture. Children with pre-existing tympanic membrane perforations (e.g., tympanostomy tubes) and those who had ear discharge that prevented detailed assessment of the tympanic membrane were excluded from the data analysis.
At least one episode of AOM occurred in 71 percent of the 831 enrolled children during the study. The three most common bacterial causes of infection were Streptococcus pneumoniae (22.8 percent), Moraxella catarrhalis (17.9 percent), and Haemophilus influenzae (16.4 percent). The most frequently encountered presenting symptoms were runny nose and cough.
Fever was reported more often when S. pneumoniae was the causative agent (60 percent of streptococcus A cases versus 45 percent of cases overall), as was earache (43 percent versus 32 percent). Eye discharge, redness, or purulence occurred more frequently when AOM was caused by H. influenzae (59 percent), compared with overall cases (21 percent).
Clinical findings on tympanic membrane examination did not differentiate well among these three bacterial pathogens. Overall, culture-positive AOM cases had somewhat higher rates of color change over more than 50 percent of the tympanic membrane (74 to 80 percent in patients with bacterial causes versus 64 percent in culture-negative cases), a bulging tympanic membrane (32 to 44 percent versus 16 percent), a flattened type B curve on tympanometry (72 to 80 percent versus 60 percent), and tympanic membrane immobility on insufflation (42 to 44 percent versus 36 percent).
The authors conclude that otitis media caused by S. pneumoniae is more likely with higher symptom severity (i.e., fever, earache), H. influenzae is more likely when eye redness or discharge is present, and no useful clinical predictors were found for AOM caused by M. catarrhalis.
editor’s note: In addition to information about which clinical findings correlate with which specific bacterial pathogens, the overall and humbling reminder I come away with after reading this article is the rough similarity in otoscopic and tympanometric findings in culture-positive and culture-negative cases of otitis media.—b.z.