Key messages

• Probiotics might prevent traveler’s diarrhea but the certainty of the evidence is low.

What is the evidence.
See evidence matrix  in Epistemonikos later

We found four systematic reviews [3],[4],[5],[6], that included seven randomized controlled trials [7],[8],[9],[10],[11],[12],[13].

What types of patients were included

Three studies only included adults [7],[11],[13].

One study included patients aged 10 to 80 years [10]. In three studies, the age range was not specified [8],[9],[12].

The included patients traveled to different destinations:

• From the United Kingdom to Belize [7]
• From Austria to Turkey/North Africa [8]
• From Denmark to Egypt [9]
• From Finland to Turkey [10]
• To warm climates [12] not specified
• From the United States to Mexico [13]
• One trial included several destinations [11]

What types of interventions were included

The trials used different probiotics and in different doses:

• Lactobacillus fermentum 10¹¹ CFU per day during three weeks or until the appearance of diarrhea [7].
• Lactobacillus acidophilus 10¹¹ CFU per day during three weeks or until the appearance of diarrhea [7] (subgroup of study above).
• Saccharomyces boulardi 5 X 10⁹ and 2 X 10¹⁰ during three weeks [8]. 
• Combination of L. acidophilus + L. bulgaricus + bifidobacterium bifidum + streptococcus thermophilus 3 x 10⁹ per two weeks [9].
• Lactobacillus rhamnosus GG 2 x 10⁹ CFU per day during 1-2 weeks [10].
• Lactobacillus rhamnosus GG 20 x 10⁹ CFU per day during 1-3 weeks [11].
• Saccharomyces cereviciae 2.5 x 10⁹ or 5 x 10⁹ and Lactobacillus acidophilus 2 x 10⁸ or 2 x 10⁹ during the travel (average 10 days for Saccharomyces and 12 days for Lactobacillus) [12]. 
• Lactobacillus acidophilus + lactobacillus bulgaricus 30 x 10⁷ at 60 x 10⁷ lactobacilli per tablet, four tablets in each meal for eight days and during 28 days [13]. 

All of the trials compared against placebo or standard treatment. 

What types of outcomes
were measured

The outcome was the development of diarrhea during the trip, defined as more than three stools per day for at least two days, or more than five stools in 48 hours.

Follow the link to access the interactive version of the Summary of Findings (iSoF) table

To whom this evidence does and does not apply

• The evidence presented in this summary applies to people traveling to various destinations.
• Although the trials used different probiotics, the overall certainty of the existing evidence is low, so any conclusion regarding differences between different types of probiotics is not reliable.

• We only included the development of diarrhea as the critical outcome for decision-making, which in general agrees with the guidelines and reviews identified.

• It is not possible to make an adequate balance between benefits and risks due to the existing uncertainty
• If the benefit were real, there would be important variation in this balance depending on different risk areas.

• Probiotics constitute a generally acceptable and well tolerated intervention by patients, although it is associated with costs.
• Patients and physicians putting more value on an uncertain benefit would probably be inclined to use this intervention. Those who place a higher value on the certainty of the evidence or costs would probably abstain from its use.
• In any case it is important to inform about the limitations of existing evidence.

• The cost of probiotics could be an important factor in the decision, especially in situations where resources are limited.
• It is not possible to make an adequate cost / benefit balance due to the existing uncertainty.

Differences between this summary and other sources

• The systematic reviews identified differ in their conclusions, so this summary partially agrees with them, especially in recognizing that the existing evidence is limited.
• The evidence presented in this summary is consistent with one of the main clinical guidelines, which makes a conditional recommendation against its use, based on evidence similar to what is discussed in this article [14].

• The probability that future evidence would change the conclusions of this article is very high, due to the existing uncertainty.
• None of the identified systematic reviews is sufficiently updated, so a new review could shed some additional light on this topic.