Does Tympanometry Predict Antibiotic Usage in Acute Otitis Media?

INTRODUCTION Acute Otitis Media (AOM) is the most common childhood infection for which antibiotics are prescribed.{1-2} Several important factors have altered the prescription practices for AOM in the past decade. North America has seen an epidemic of microbial resistance, attributable in a large part to the over-prescription of antibiotics.{3-4} Evidence has shown that AOM is commonly over diagnosed and antibiotics are prescribed unnecessarily.{5-7} In addition a number of studies comparing antibiotic treatment to placebo, although proving superiority for antibiotic treatment, had very high rates of resolution with placebo. A meta analysis of 7 RCT's show a 73% success rate for Amoxicillin versus 60% for placebo.{8}

These results prompted interest in a watch and wait strategy for the treatment of AOM for children 6 months to 10 years of age. Three important studies were performed assessing the outcomes of delaying antibiotics for 48-72H, two in primary care{9-10} and one in a pediatric emergency department.{11} All three showed no difference in outcomes with 2-4 week follow-up. There was a significant reduction in antibiotic usage with the watch and wait approach, a reduction of about 70%. These studies led both the American Academy of Pediatrics and the Canadian Pediatric Society to recommend adopting a conservative non-antibiotic treatment strategy for AOM in the first 48-72H.{12} However in early 2011, 2 papers were published that suggested that antibiotic use in AOM was beneficial.{13, 14} What set both of these two papers apart from other papers was the definition of acute otitis media: in one study the children were enrolled by study clinicians who were otoscopists who had successfully completed an otoscopic validation program, in the second study middle ear fluid had to be present by means of pneumatic otoscopy. The question then arises, is the treatment of otitis media really a question that concerns the treatment, or is it a question of diagnosis? The published correspondence that these two papers generated, suggested that diagnosis of AOM is indeed a concern. A technique named tympanometry could prove to be useful.

Tympanometry is a well established technique for documentation of middle ear effusion. Tympanometry measures the compliance of the tympanic membrane over a range of pressures. A graphic curve is generated which can be compared to normals or examples of pathologic conditions. Primary care physicians have used this technique successfully among children with and without a diagnosis of AOM.{15} Two studies involving tympanometry and otitis media{16-17} have shown tympanograms consistent with clear middle ear effusion(Type B) in 50-60% of patients clinically diagnosed with AOM. This strongly suggests that AOM is being over diagnosed! Interestingly Spiro et al showed that rates of antibiotic prescription were not different in physicians who were aware of tympanogram results and those who were blinded. This indicates a lack of knowledge around the impact on outcome of the initial tympanogram.

Currently at the Stollery, (and as suggested by CPS and AMA) well children who are diagnosed with AOM are given a prescription for antibiotics, but told to wait 48 hours before filling them, in the expectation that many of these children will have a complete resolution of their symptoms. They are encouraged to take analgesics to keep them comfortable. However, the current state of knowledge indicates that antibiotics provide superior symptom control in the first 24-48H and provide superior resolution rates to placebo in clinically diagnosed AOM. The delayed antibiotic strategy has similar long term outcomes to immediate antibiotic treatment. It is not clear if patients with middle ear effusion documented by adjunctive tests, such as tympanometry represent a distinctly different group than those diagnosed by observation of the tympanic membrane only. Spiro's study indicates that physicians do not know and therefore are not changing their practice on the basis of tympanogram results.

This then brings us to the investigators' primary research question. Are those children aged 6 months to 16 years who attend the Stollery Emergency Department and are diagnosed with AOM (and sent home with conservative management) more likely to fill a prescription for antibiotics over the next 7 days if their tympanogram is type B rather than types A or C?