Monaz: Hello, I'm Monaz Mehta, editor in the Cochrane Editorial and Methods department. Infectious diarrhoea is responsible for many thousands of deaths every day around the world and probiotics have been suggested as a possible treatment. The relevant Cochrane Review was updated for the second time in December 2020 and first author, Shelui Collinson from the Liverpool School of Tropical Medicine in the UK describes the latest findings in this podcast.

Shelui: Acute infectious diarrhoea occurs in people of all ages but especially in children in poorer countries. It is caused by many different bacteria, viruses, and parasites. Most episodes last only a few days but, when it's severe, the loss of water and salts from the body causes severe dehydration and even death. This makes diarrhoea the third leading cause of death in children worldwide.
The most important aspect of clinical management is to prevent or treat dehydration by giving extra fluids. However, if interventions shorten the duration of the illness these would also have several benefits and probiotics have been suggested as something that might do this.
Probiotics are live bacteria and yeasts that are thought to restore the natural balance of microbes in the intestines when this has been disrupted by illness. Probiotics are often described as "good" or "friendly" bacteria and they may be able to shorten the duration of diarrhoea by acting against harmful microbes or reducing the gut damage that occurs in infectious diarrhoea.
For this latest update, we found 82 randomised trials involving more than 12,000 people with acute diarrhoea, the great majority of them children. Most of the studies were done in richer countries. Some were done in the community and some in people admitted to hospital. All patients received appropriate rehydration fluids, and were randomised to a probiotic or a placebo (or “dummy”) preparation or no additional treatment. 
The studies were designed and carried out in many different ways, with a wide variety of probiotics being tested and the effects of probiotics on diarrhoea varied markedly across the studies. Looking at the quality of the research, we assessed many of the studies to be of low quality and we also suspected that some studies may not have been published if they failed to show that probiotics were effective. We would not have been able to find these 'negative' studies or include them in our review.
As a result of the deficiencies in much of the evidence base, we focused in on just those studies that we assessed to be of high quality. For our main outcomes, two trials that involved nearly 1800 children provided moderate certainty evidence that the numbers of children who had diarrhoea that lasted longer than 48 hours were similar for the probiotic and control groups. There was also no difference in the duration of diarrhoea in six trials involving just over 3000 people, although the certainty of evidence was very low for this finding. 
In addition, we did not find that the difference between the probiotic and control groups depended in any important way on the person's age, socioeconomic level or severity of diarrhoea; whether or not they were given antibiotics or zinc; whether the diarrhoea was caused by rotavirus and which world region the study was done in. We also did not find clear evidence of effectiveness for any specific probiotic preparation.
Some studies reported on other important outcomes; and, again, we did not find any differences between the probiotic and control groups for how many people had diarrhoea lasting longer than 14 days, how many people were admitted to hospital with diarrhoea in studies done in the community or how long people stayed in hospital.
In summary, despite the large number of trials, we found that the quality of the evidence was weak. When we restricted our analysis to high-quality trials, we found that probiotics probably make little or no difference to the number of people who have diarrhoea lasting 48 hours or longer, and we remain uncertain whether probiotics reduce the duration of acute diarrhoea. On this basis, our take home message is that our findings do not support the use of probiotics for treating acute diarrhoea.

Monaz: If you would like to read the full review, including its implications for practice and research, it's available in full online. Just go to Cochrane Library dot com and search 'probiotics and diarrhoea' to find it.