REVIEW QUESTION

Are probiotics safe and effective in the prevention of acute upper respiratory tract infections (URTIs)?

TYPE OF REVIEW

A systematic review of 13 randomized controlled trials (RCTs) with a meta-analysis of 12 of those trials.

RELEVANCE FOR NURSING

URTIs include the common cold, inflammation of the trachea and larynx, rhinosinusitis, and otitis media. In the United States, acute URTIs are the most common ailments for which patients seek medical care. Up to 75% of antibiotics prescribed in high-income countries are to treat acute URTIs. Antibiotic overuse is a major contributor to the development of antibiotic-resistant bacteria.

Probiotics are live microorganisms that may improve health by bolstering local and systemic immunity. Their mechanism of action is thought to occur through enhanced phagocytic capacity and activity, stimulation of higher levels of specific immunoglobulins, and enhancement of gut barrier functions. Probiotics are often consumed in fermented foods (such as yogurt) or dietary supplements; the most common strains are Lactobacillus spp and Bifidobacterium spp. Although research in the field of probiotic use has been conducted for over a century, the effect of probiotics on acute URTIs and their possible untoward effects in humans are not yet fully understood.

CHARACTERISTICS OF THE EVIDENCE

This review included 13 RCTs comparing probiotics with placebo or no treatment in the prevention of acute URTIs in people at risk for acute URTIs; 12 trials were included in the meta-analysis. Data from 3,720 participants in RCTs conducted between 2002 and 2013 in eight countries were pooled for analysis. The probiotic intervention included any probiotic mixture, strain, route, or dose administered for more than seven days.

Probiotics were found to be more effective than placebo-reducing the number of participants who experienced episodes of acute URTI by about 47% and the duration of an episode by about 1.89 days. Probiotics also slightly reduced antibiotic use and cold-related school absences.

In older adults, although probiotics did not reduce the rate of URTIs, the duration of the infection was decreased. Subgroup analysis of all age groups suggest that probiotics reduced the number of children experiencing acute URTIs. Overall, probiotics were found to be safe with few adverse effects (mostly gastrointestinal symptoms).

The overall quality of the evidence was low or very low largely because some of the trials had limitations in their design, methods, and reporting; a small sample size; or a potential for bias because of financial support from the manufacturer of the tested probiotics.

BEST PRACTICE RECOMMENDATIONS

Probiotics are likely more effective than placebo in reducing the number of episodes of acute URTI, the average duration of these episodes, antibiotic use, and URTI-related school absences.

RESEARCH RECOMMENDATIONS

Although probiotics may be more beneficial than placebo in the prevention of acute URTI, especially in children, higher-quality evidence and additional RCTs are needed. Future RCTs should be designed to assess common outcomes, incorporate an adequate description of blinding and concealment of the allocation sequence, include adverse effect outcomes, focus on older people, and not be unduly influenced by manufacturer funding.

REFERENCE