Current guidelines recommend treatment of high-dose amoxicillin for children with acute otitis media (AOM) who are at high risk for infection with non-susceptible Streptococcus pneumoniae (NSSP). This includes all patients who are younger than two years, attend day care, or have recently been exposed to antibiotics. High-dose amoxicillin (80 to 90 mg per kg per day, twice the standard dosage) may not be needed if NSSP prevalence is low in the local area. However, prevalence data on NSSP is limited. Garbutt and colleagues used data from nasopharyngeal cultures to estimate the prevalence of NSSP in one city, and to develop community-specific treatment guidelines based on local susceptibility.
Patients from seven pediatric offices were enrolled in the study; the inclusion criteria were age younger than seven years and a new diagnosis of AOM or one of several other upper respiratory infections. A posterior nasopharyngeal swab was obtained from each child. Minimum inhibitory concentrations (MIC) were then measured on S. pneumoniae specimens. Isolates with an MIC of 0.12 μg per mL or higher were considered resistant to penicillin and were labeled NSSP; isolates with an MIC of greater than 2 μg per mL were considered resistant to standard-dose amoxicillin and were labeled NSSP-A. Parents completed a survey identifying risk factors for infection with NSSP, including day-care attendance, number of children at home, and recent antibiotic use.
Of the 212 participating children, 70 (33 percent) had nonspecific upper respitory infection (URI) and 58 (27 percent) had AOM, the most frequent diagnoses. Twenty-nine (50 percent) of the children with AOM had positive nasopharyngeal swabs, as did 11 (48 percent) of those with otitis media with effusion, eight (33 percent) of those with acute sinusitis, and 30 (43 percent) of those with URI. About one quarter of isolates were highly reisistant and one quarter were intermediately resistant to penicillin. NSSP prevalence in the study sample was 19 percent. Attendance at a day-care center was independently associated with higher NSSP carriage. Of the 85 S. pneumoniae isolates, six fit the definition of NSSP-A, a prevalence of 7 percent among isolates, and 3 percent among the study sample. In the NSSP isolates, there was a high resistance to other antibiotics as well as to penicillin.
In this study population, the authors calculate, standard-dose amoxicillin would have been effective in most patients treated for AOM. No more than an estimated 3 percent would have failed treatment. This percentage may in reality be even less because, among other reasons, nasopharyngeal carriage overestimates the presence of the organism in the middle ear. the authors conclude that treating the local population with standard-dose amoxicillin would be adequate, with high-dose treatment reserved for day-care attendees. Although nasopharyngeal carriage does not correlate perfectly with middle ear isolates, this study demonstrates that it is relatively easy to measure local prevalence of NSSP and derive treatment recommendations accordingly. Still needed are accurate determinations of amoxicillin resistance and more information regarding the impact of pneumococcal conjugate vaccine on NSSP prevalence.