Donovan et al.
1996. Investigators challenge tested
patients in an Environmental Exposure Unit with concentrations of ragweed of
2500 to 3000 grains/m3. The
purpose of the study was to test the efficacy of immunotherapy for
ragweed. Three groups of patients were
used in the study including ragweed sensitive on immunotherapy >2 years,
ragweed sensitive with no immunotherapy, and non-sensitive to ragweed. It was found that the immunotherapy patients
had fewer nasal symptoms.