Probiotic bacteria given as therapies for diarrhoea reduce the length of time sufferers are affected and lessen the chance of episodes continuing for more than four days. These are the findings of a new systematic review by Cochrane researchers.

Every year, diarrhoeal diseases kill nearly two million people in developing countries, mostly young children. The main treatment is rehydration fluids, but these do not tend to reduce the length of illness, which is crucial in reducing the risk of persistent diarrhoea. Probiotics, so-called "good bacteria", may help in a variety of different ways including eliminating the bacteria, viruses or parasites responsible, for example, by competing for the same nutrients. A previous Cochrane review showed benefits with probiotics in diarrhoeal disease, but the current report reviews data from a far larger evidence base.

The researchers reviewed data from 63 trials involving a total of 8,014 patients, over four times the number involved in the previous study. 56 trials focused on infants and young children. Giving probiotics in conjunction with rehydration fluids reduced the duration of diarrhoea by around a day and reduced the risk of diarrhoea lasting four or more days by 59%. No serious adverse effects were reported in the trials and although vomiting was quite common it also occurred with placebos.

"A striking finding of this review is that most trials reported that probiotics reduced diarrhoea," said lead researcher Stephen Allen of the School of Medicine at Swansea University, UK. "The beneficial effect was consistent and significant across many different types of trials."

"There were no adverse effects, so these therapies can be used safely in addition to rehydration fluids. However, more research needs to be carried out on the specific strains of bacteria that are effective in treating diarrhoea and on preventing the progression from short-term to persistent diarrhoea," Allen said.

A second review, by a separate group of Cochrane researchers, examined the use of probiotics for treating persistent diarrhoea reviewing data from trials undertaken exclusively in children. The review found that probiotics can reduce the length of an episode of persistent diarrhoea, however, the authors stress that the review was based on just four trials involving 464 patients and therefore provides only limited evidence of benefit.