With more than 100 different serotypes for rhinovirus, and a number of other virus families that are common causes of cold infections, it is highly unlikely that prevention of colds by immunization ever will be possible. Pharmacologic treatments for colds also have limited usefulness, although more than $300 million is spent on these medications each year in the United States. A host of different echinacea plant preparations have been studied for prevention and treatment of colds, but most published trials have failed to show statistically significant efficacy. Although some studies showed trends toward symptom-relief benefits, data interpretation was made difficult because of the wide variety of natural cold causes. Sperber and colleagues report on the use of echinacea within an experimentally induced rhinovirus infection model, which was designed to provide more standardized conditions for the evaluation of the possible benefits of this common herbal remedy.

The trial used a pressed juice formulation of above-ground echinacea plant parts. Forty-eight adult volunteers were randomized to receive 2.5 mL of a liquid echinacea preparation or placebo, which was taken three times a day for 14 days. After seven days, each participant was inoculated with an intranasal dose of rhinovirus RV-39 and then sequestered in a hotel room for the following three days. Rhinovirus infection was defined as a fourfold rise in RV-39 antibody titer or a positive viral culture from intranasal lavage specimens. Participants recorded symptom severity three times a day for the first seven days after inoculation, then once a day until the end of the trial. Two volunteers were excluded from the final analysis; one because of an elevated RV-39 antibody titer before inoculation and another because of the onset of cold symptoms before the study began.

The proportion of echinacea and placebo recipients who developed an elevated RV-39 antibody titer or positive viral culture after inoculation was similar (92 and 96 percent, respectively). During the postinoculation treatment phase, fewer participants in the echinacea group (59 percent) had cold symptom scores above the cutoff defined as clinical infection compared with the placebo group (86 percent), but the difference did not reach statistical significance. The study sponsor declined to proceed with a planned expansion of the trial after review of these preliminary results.

The authors conclude that echinacea is not effective for prevention of rhinovirus infection. Although there was a trend toward more symptom relief with the use of echinacea after infection, this benefit could not be statistically confirmed because of the limited sample size of the study.