We found that preventive treatment with osteopathic manipulation did not result in a statistically significant decrease in the risk of AOM in otitis-prone children. Treatment with an alcohol extract of Echinacea purpurea root and seeds at times of upper respiratory infection was associated with a modestly increased risk of AOM. This effect was of borderline statistical significance and may have been due to chance.
As noted, the randomization process resulted in an unequal distribution of certain otitis risk factors among treatment groups. The group receiving echinacea alone appeared to be at higher risk based on several factors, and this chance occurrence may have been responsible for the higher rate of otitis in the echinacea group. We adjusted for known confounding factors, resulting in modest changes in relative risk estimates, but the possibility of incomplete adjustment, or unmeasured confounding by other factors cannot be excluded.
This is the first randomized, placebo-controlled trial of Echinacea purpurea for the prevention of AOM. We chose to treat children at the time of upper respiratory tract infections, rather than using a prolonged preventive regimen, based on the finding that echinacea appeared to be more effective in treatment than prevention of URI in adults . Two subsequent randomized trials did not confirm this pattern in children. Taylor and colleagues found the pressed juice of E. purpurea aerial plant to be of no benefit to children in treatment of the common cold . Cohen reported a significant reduction in colds and other respiratory outcomes following preventive use of a product containing liquid extracts of E. purpurea aerial plant, E. angustifolia root, propolis, and vitamin C . The latter study also showed a decreased risk of acute otitis media with the echinacea product, but was not designed to measure this outcome in a rigorous way. Recent studies have confirmed our premise that AOM in children is a frequent complication of viral upper respiratory tract infection [24, 25].
Research on the therapeutic use of echinacea is complicated by the fact that there are three species of echinacea in common use, and preparations are made from various combinations of leaves, flowers, roots, and seeds of the plant. Furthermore, various methods of preparation are used, including alcohol or glycerin extraction, desiccation, and juicing. These issues are discussed elsewhere with respect to the present study . Our results cannot be generalized to other forms of echinacea.
One previous study evaluated OMT for prevention of AOM in otitis-prone children . The authors reported a statistically significant decreased frequency of AOM episodes and fewer surgical episodes among treated children. That protocol called for 9 osteopathic treatment visits, compared with 5 in the present study. As noted by the authors, that study did not have a placebo control, and the control group had a very high dropout rate, a combination of factors with a significant potential to introduce bias.
The main limitations of this study were small sample size and incomplete compliance with osteopathic treatments and follow-up visits. Our final analysis involved 84 subjects, yielding 73% power to detect a 50% risk reduction under our initial assumptions. The borderline increased risk associated with echinacea treatment make a protective effect of this form and dosage schedule of echinacea very unlikely, despite the sample size.
Because we were able to identify episodes of AOM through medical record review, the incomplete compliance with follow-up pediatrician visits had limited impact on our findings. However, it is possible that the lack of a statistically significant benefit found for OMT was the result of inadequate compliance with OMT visits. An analysis restricted to subjects attending 3 or more treatment visits did not suggest a greater protective effect of OMT, but the sample size was small. On the other hand, research personnel exerted considerable effort at getting subjects to these visits, with limited success, perhaps because the children were not ill at those times. An analysis of the reasons for limited participation by families with OMT may be useful for future OMT research.
An ancillary purpose of this study was to determine if a suitable sham for osteopathic manipulation could be devised. A previous study of sham chiropractic treatment in children did not evaluate how parents perceived the sham treatment. We hoped to be able to show that parents would be unable to distinguish examination alone from examination and concurrent treatment. In fact, about 20% of parents of sham recipients (versus 4% in the true treatment group) correctly thought that the child was receiving sham manipulation. However, the large majority of parents of sham recipients could not tell that the "sham manipulation" was placebo. Some osteopathic physicians believe any "hands-on" contact has potential therapeutic benefit. To the extent this is true, our "sham" treatment could mask an actual benefit of OMT.