Guillemard E.
Danone Research, Palaiseau, France

Acute upper and lower respiratory tract infections (RTIs) are endemic in the general population and a major cause of morbidity and mortality resulting in significant economic and social costs. Recently a number of clinical trials showed that specific well-characterized probiotics can exert a beneficial effect in reducing the morbidity associated with RTIs. Among them, a multicenter, double-blind, randomized, placebo-controlled clinical trial (Prodeus et al.,JPGN, 2016) investigated the effect of a fermented milk product containing the Lactobacillus casei CNCM I-1518 strain, on respiratory and gastro-intestinal common infectious diseases (CIDs) in 600 children attending day-care centers in Russia. Children consumed the product twice-daily for 3 months followed by a 1-month follow-up period. The primary outcome was the incidence of CIDs during the product consumption period. The results showed no significant difference in the incidence of CIDs between the two groups (primary outcome), however, a significantly lower incidence of rhinopharyngitis, the most frequent CID, was observed in the group consuming the probiotic product compared to the control product group (RR[95% CI]=0.82[0.69;0.96];p=0.017) during the entire study period. This effect is supported by two studies reporting a significant effect of the same product in reducing the incidence rate of upper-RTI (URTI) in children attending day-care centers in the USA, as well as the average and cumulated duration of URTI and rhinopharyngitis in free-living elderly.

These studies were recently included in meta-analyses assessing the effectiveness of probiotics (any strains) in the prevention of acute URTIs or in the reduction of RTI duration in otherwise healthy children, adults or elderly. These meta-analyses showed promising results supporting a beneficial effect of probiotics on the clinical outcomes related to RTI and on the associated antibiotic use or absenteeism. However, some limitations have been pointed out that impacted the quality of evidence including: high or unclear risks of bias (according to Cochrane approach), a small sample size or the methods of RTI reporting used in individual studies, and the high heterogeneity between the pooled trials. These meta-analyses did not provide information on the most effective strains considering that probiotic effects are generally considered strain-specific.

The effect of probiotics on RTI is supported by plausible mechanisms of action described in both animal and humans. This field of research has recently benefited from interesting results on the role played by the immune system and the microbiota in the airways, an emerging subject of investigation which showed that a specific microbiota composition in the respiratory tract could be associated with lung diseases, and risks of respiratory infections in humans.
Therefore an increasing number of data support that probiotic interventions could be beneficial against RTI. Nevertheless, meta-analysis with high quality of evidence and less heterogeneity between the included studies are still needed to further reinforce this demonstration. This might be achieved by focusing on specific sub-populations and/or specific probiotic strains interventions. Furthermore, it is important to gain a better understanding of the associated mechanisms underlying the probiotic effects which may help in selecting the most efficacious strains.

Keywords: Respiratory infections, Probiotics, Lactobacillus casei CNCM I-1518/DN-114 001

Guillemard E. (2016). Probiotics and respiratory tract infections: What´s new?
Conference Proceedings of IPC2016. Paper presented at the International Scientific Conference on Probiotics and Prebiotics, Budapest (p. 27.). IPC2016

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