Bacterial pathogens of otitis media and sinusitis: Detection in the nasopharynx with selective agar media

Carriage rates for the bacteria[ pathogens associated with otitis media (St reptococcus pneumoniae (SP), Hemophilus influenzae (HI), and Moraxella cata rrhalis (MC)) are of interest. Culture on three selective agars was compare d with culture on two standard agars to determine the more accurate method for detection of these species in the nasopharynx of healthy children. Week ly samples were obtained in winter from 18 healthy children (ages 1 through 9 years) as part of a longitudinal study. A 0.1-mL. sample of 116 nasophar yngeal aspirate/washes was inoculated onto each of five agars. Two were sta ndard (sheep blood and chocolate), and three were selective (blood with gen tamicin for SP; chocolate with vancomycin, bacitracin, and clindamycin for HI; blood with amphotericin B, vancomycin, trimethoprim, and acetazolamide for MC). One technician read the standard plates and another the selective; both were blinded to the results of the other. SP was found in 44% of samp les with selective agar versus 25% with standard agar; HI was found in 31% with selective versus 9% with standard; MC was found in 56% with selective versus 37% with standard. Overall, 80% of samples had one or more pathogens detected with selective agars as compared with 58% with standard agars (P =.0004). Selective agars were more accurate than standard agars for detecti ng otitis pathogens in the nasopharynx, where they are a common part of nor mal flora in healthy children.