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Echinacea for prevention of recurrent respiratory tract infection.

Schapowal A, Klein P, Johnston SL. 2015. Echinacea reduces the risk of recurrent respiratory tract infections and complications: A meta-analysis of randomized controlled trials. Advances in Therapy 32:187-200.

Respiratory tract infections (RTIs) are some of the most commonly occurring illnesses worldwide and demonstrate a high propensity of recurrence. Such infections can be debilitating and immune depleting, with physical damage to the airway increasing risk of infection, subsequent recurrence and risk of complication. With limited therapeutic options available for acute infections, Echinacea spp (echinacea) extracts, which have traditionally been used to support the immune system, are of great interest. Previous meta-analyses have assessed the role of echinacea in prevention or treatment of an acute phase infection, but recurrent infection or complications have not been included. The aim of the present study was to review and evaluate existing literature and through a meta-analysis assess the preventative effect of echinacea on recurrent respiratory infection and complications.

A systematic review of ten databases including MEDLINE, MBASE, CAplus and BIOSIS was undertaken by two reviewers searching for clinical trials that studied recurrent respiratory infections and complications on treatment with echinacea in a generally healthy population. There were no restrictions for year or publication status. When different echinacea preparations or doses were used in parallel within a single study, the data from the different treatment arms were pooled. The primary outcome assessed was recurrent infection risk, defined as the total of second, third, fourth and fifth episodes under echinacea or placebo continuous treatment for 2-4 months. Complications and associated antibiotic intake as well as safety of treatment were also assessed. After searching and assessing the appropriateness of studies found, the data from six clinical trials were extracted and pooled for meta-analysis.

Data on recurrent respiratory infections from the six clinical trials included a total of 2458 participants who received a variety of echinacea extracts or placebo for up to 4 months. Different forms of echinacea were used, with four studies employing ethanol/glycerol extractions for E. purpurea/E. angustifolia (500-4000mg/day), and two using pressed juice of E. purpurea (6200-10,000mg/ day). Dosing ranged from once daily to four times daily over a period between 2 and 4 months. Of note, one study included in the meta-analysis employed a herbal preparation containing E. spp, propolis and vitamin C in a glycerol extract, while a second study used a combined herbal extract of E. angustifolia, eupatorium and baptisia. All trials individually reported a lower incidence for recurrent infection in echinacea-treated versus placebo-treated groups but only two of these reached statistical significance.

When the data was pooled, the meta-analysis revealed a significantly reduced risk of recurrent respiratory infection (relative risk (RR) 0.649) in echinacea-treated versus placebo-treated groups. Further investigations were also undertaken in a number of subgroup analyses. When comparing ethanolic/glycerol echinacea extract to pressed echinacea juice extract, the former treatment appeared to offer greater risk reduction (RR = 0.542). Additionally, preventative benefits were assessed in a subgroup population with reported risk factors to infection such as stress, smoking, poor sleep, and presumed immune weakness, with authors reporting superior protective effects in these groups compared to the overall population. Complications including pneumonia, otitis media/externa, and tonsillitis/pharyngitis were also less frequent in the echinacea-treated groups (RR = 0.503), and associated with a decreased need for antibiotics.

The heterogeneity of the tested preparations is a limitation of the study and is reflective of the variations and challenges in analyzing such data. Differences in species, dosing protocols, extraction techniques and duration of treatment contributed to the heterogeneity. Furthermore, the authors did not comment on the possible influence on the meta-analysis outcomes when other ingredients were used in the trials employing combined herbal treatments. The effects from these trials on lowering RTI risk cannot be assumed to be due to echinacea alone, and may have influenced the overall results of pooled data.

Overall, this study provides further insight and supports the role of echinacea in the RTIs, with data indicating an increased benefit upon long-term echinacea supplementation (2-4 months) as a preventative agent for recurrent infections and complications. The authors note that people at most benefit may be those with a presumed lower immune function and consequently high susceptibility. As meta-analyses allow for the pooling of data when studies are sufficiently similar in design and endpoint, they enable interpretation and observation of effect across a greater population. These results provide some clarity through the pooling of data from previous individual studies which have had inconsistent and non-significant findings.
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Publication:Australian Journal of Herbal Medicine
Article Type:Abstract
Date:Sep 1, 2015
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