Review
Probiotics for the prevention of respiratory tract infections: a systematic review

https://doi.org/10.1016/j.ijantimicag.2008.11.005Get rights and content

Abstract

We evaluated the clinical evidence regarding probiotic use for the prevention of respiratory tract infections (RTIs). Randomised controlled trials (RCTs) studying the effects of probiotics for the prevention of upper or lower RTIs were systematically identified. Fourteen RCTs (twelve involving healthy subjects and two involving patients with RTIs) were included. Various Lactobacillus strains were used in seven RCTs, combinations of Lactobacillus and Bifidobacterium strains were used in five RCTs, and a Bifidobacterium strain and a non-pathogenic Enterococcus faecalis strain were used in one RCT, respectively. In ten RCTs no difference was found regarding the incidence of RTIs in the probiotic arm compared with the control arm, whereas the remaining four RCTs favoured the use of probiotics. Reduction in the severity of symptoms related to RTIs was noted in five of six RCTs that provided relevant data. In three of nine RCTs that provided relevant data, the clinical course of RTIs was shorter in the probiotic arm, whereas no difference was found in the remaining six RCTs. In conclusion, probiotics may have a beneficial effect on the severity and duration of symptoms of RTIs but do not appear to reduce the incidence of RTIs.

Introduction

Respiratory tract infections (RTIs) affect a large proportion of the population and are associated with substantial morbidity and mortality. Antibiotics are often used inappropriately for the treatment of these infections, leading to increasing bacterial drug resistance rates [1], [2], [3]. Therefore, use of new methods for the prevention or treatment of RTIs is an appealing approach currently under investigation.

Probiotics are by definition live organisms that, when administered in adequate quantities, confer health benefits to the host [4]. Recent scientific data demonstrate potential benefits of the administration of probiotics for urogenital, gastrointestinal and surgical infections [5], [6], [7], [8], [9], [10], [11], [12], [13]. The clinical utility of probiotics may extend to fields such as allergic disease and cancer [14], [15], [16], [17], [18], [19], [20], [21], [22]. The effects of probiotics on human RTIs have not been adequately substantiated. However, experimental studies on animal models support the hypothesis for a potentially beneficial effect of probiotics on human RTIs. This could be mediated by the stimulation of cellular and humoral immunological functions [23], [24], [25], [26], [27], [28], [29].

In this regard, we aimed to review systematically the available evidence regarding the potential utility of the administration of probiotics for the prevention or amelioration of RTIs.

Section snippets

Data sources

The PubMed, Cochrane Central Register of Controlled Trials (CENTRAL) and Scopus databases were searched up to 5 February 2008 to identify clinical trials eligible for inclusion in this review. The literature search strategy used in PubMed was ‘respiratory tract infections AND (probiotics OR prebiotics OR synbiotics OR Lactobacillus OR Bifidobacterium)’. The search term applied to both CENTRAL and Scopus was ‘(respiratory tract infections) AND (probiotics)’.

Study selection criteria

Randomised controlled trials (RCTs) referring to the clinical utility or safety of the administration of probiotics for the prevention of upper or lower RTIs were considered eligible for inclusion in this review. Studies with a cross-over design, animal studies, studies reported in abstracts presented in scientific conferences, and studies published in languages other than English, German, French, Italian and Spanish were excluded from the review. Two reviewers (GCM and EKV) independently

Data extraction

Data extracted from each of the included RCTs referred to the study design, the characteristics of the included populations, the type of RTIs, the type and form of the administered probiotic, the duration and dosing schedule of probiotic treatment, any concomitantly administered therapy, the outcomes regarding RTIs and any treatment-related adverse events observed.

Respiratory tract infections

RTIs were infections of the upper respiratory tract, including common cold, acute otitis media, tonsillitis/tonsillopharyngitis, sinusitis and recurrent sinusitis, as well as infections of the lower respiratory tract, including bronchitis and pneumonia.

Probiotics

Probiotics are dietary supplements containing potentially beneficial bacteria or yeasts. Commonly used probiotics include lactic acid bacteria (such as Lactobacillus acidophilus, L. casei, L. lactis, L. plantarum, L. reuteri, L. rhamnosus, L.

Methodological quality of the included randomised controlled trials

The methodological quality of the included RCTs was assessed using the Jadad criteria. According to these criteria, reporting of data regarding the process of randomisation, blinding and study withdrawals is assigned one point for each one of the above study characteristics. In addition, one point is assigned or subtracted depending on whether the quality of each one of the randomisation and blinding procedures is deemed adequate. Five points is the maximum score that can be attributed to a

Selected randomised controlled trials

The searches performed in PubMed, CENTRAL and Scopus generated a total of 109, 15 and 65 search results, respectively. Among these, 14 individual RCTs were regarded as qualifying for inclusion in this review [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44]. The detailed process of the selection of eligible trials is depicted graphically in Fig. 1.

Discussion

The main finding of this review is that probiotics, when taken prophylactically by healthy individuals or by patients with a RTI, do not reduce the incidence of RTIs, as shown in the majority of included RCTs. However, a beneficial effect of the use of probiotics on the severity and duration of subsequent RTIs was documented in the majority of relevant RCTs. Furthermore, the administration of probiotics appeared to have a good safety profile, since the majority of the included RCTs did not

Summary points

  • Fourteen RCTs evaluated the prophylactic administration of different probiotics for the prevention of upper or lower RTIs in adults or children.

  • A beneficial role of probiotics in reducing the incidence of RTIs was found in four of these trials, whilst no effect was found in ten trials.

  • Reduction in the severity of subsequent RTIs was found in five of six trials that reported relevant data.

  • A reduction in the duration of RTIs was found in three of nine trials.

  • Minor adverse events related to

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