Diarrhoea is defined by the World Health Organization (WHO) as the passage of three or more loose or watery stools per day [
1]. The etiological factors related to diarrhoea include infections from bacterial, viral or protozoal organisms, and other causes such as medications (antibiotics, non-steroidal anti-inflammatory drugs and chemotherapeutic agents) [
2]. Based on the symptoms and duration, diarrhoea could be acute or chronic and infectious or non-infectious. Acute diarrhoea lasts less than 2 weeks and is commonly due to infections, while chronic lasts longer (> 2 weeks) and is generally non-infectious. According to the global burden of disease study on the burden of diarrhoea in India from 1990 to 2019, the mortality rate per 100,000 population for all ages was 45.46, under 5 years was 47.24; 5–14 years was 6.31, 15–49 years was 6.65, 50–69 years was 62.76, and > 70 years was 682.21 [
3]. The prevalence of diarrhoea is highly heterogeneous across Indian states, and it ranged from 0.1 to 33.8% in the period between 2007 and 2008 and 0.6–29.1% in the period between 2015 and 2016 [
4]. A recently published Indian study by Shrivastava et al. evaluated the prevalence of diarrhoea among older Indian adults between 2017 and 2018 [
5]. About 15% of older adults reported to the physician with complaints of diarrhoeal episodes over the preceding 2 years. Every year, over 10 million patients suffer from diarrhoea in India, and over 1000 deaths are reported consequently [
6]. Of these cases, 90% are attributed to unsafe drinking water, inadequate sanitation and poor hygiene [
7]. The mainstay of managing diarrhoea involves maintenance of hydration by oral rehydration or intravenous fluids. Oral rehydration solution is intended to decrease the mortality and morbidity due to diarrhoea by restoring hydration and electrolyte balance [
8].
Apart from rehydration strategies, probiotics are also used in the management of diarrhoea [
9]. A retrospective, multicentre, electronic medical record (EMR) study by Ragavan et al. evaluated the effects of
Saccharomyces boulardii against acute diarrhoea in children. A significant reduction in the frequency of stools and duration of diarrhoea was noted in the
Saccharomyces boulardii group versus the control group [
9]. Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host [
10]. The seven core genera of microbial organisms most often used in probiotic products are
Lactobacillus, Bifidobacterium, Saccharomyces, Streptococcus, Enterococcus, Escherichia, and
Bacillus [
11]. Yeast probiotics differ from bacterial probiotics in size, cell wall composition, antibiotic resistance and metabolic properties [
12,
13]. Compared with bacterial probiotics, yeast cells are naturally resistant to antibiotics, as they are fungi, and there is no observed DNA exchange pertaining to antimicrobial resistance genes [
14]. The only yeast genus that has been proven effective as probiotic in humans in double-blind studies is
Saccharomyces [
15]. Existing evidence strongly suggests that the efficacy of probiotics is both strain-specific and disease-specific [
16]. The probiotic actions demonstrated by a particular strain of yeast are not extrapolatable to other strains.
Saccharomyces boulardii (
S. boulardii) CNCM I-745 is the first identified yeast strain that has been studied for use as a probiotic in human medicine. A study by Dinleyici et al. established that
S. boulardii significantly diminished the duration of diarrhoea by about 24 h in the Western world, in both adults and children [
17]. Multiple clinical studies have discussed the benefit of
S. boulardii in the management of both adult and paediatric diarrhoea associated with various causes, whether it be antibiotics or
Clostridium difficile (
C. difficile) infection [
18,
19]. A systematic review and meta-analysis by McFarland et al. noted that
S. boulardii CNCM I-745 showed the strongest effect on decreasing the diarrhoea duration, as well as hospital stay in paediatric acute gastroenteritis cases [
20]. There is a lack of Indian studies which have assessed the effectiveness of
S. boulardii CNCM I-745 in adult diarrhoea, showing reduction in duration as well as the frequency of loose motions. We aimed to evaluate the effectiveness of
S. boulardii CNCM I-745 in adult Indian patients with diarrhoea with the help of a retrospective, multicentre, comparative study. The study also evaluated the effectiveness of
S. boulardii CNCM I-745 in comparison to non-probiotic treatment (control group) in adult diarrhoea patients. Diarrhoea is a major concern in India, with high morbidity and mortality related to it. In a study by Joseph et al.
6 the monthly prevalence rate of diarrhoea in India was reported as 12%, which was more than the monthly prevalence rate of 5.1 % reported from the USA [
21]. Unsatisfactory living conditions and poor sanitation as a consequence of the population explosion in the country are significantly associated with presence of diarrhoea in Indian households.
6 If the diarrhoea is not controlled in time, malabsorption can affect the individual, leading to malnutrition and unintentional weight loss. Dehydration and severe renal damage from the dehydration are potential complications as well. Abnormalities in serum electrolytes can also be problematic and necessitate monitoring for replenishment requirements [
22]. Hence, there is an urgent need for effective treatment modalities to control diarrhoeal episodes. Numerous clinical studies have noted the benefit of
S. boulardii in the management of diarrhoea, but there remains a dearth in published real-world experience with the probiotic. Usually, the quality of the evidence produced in a randomized controlled clinical trial (RCT) holds greater credibility than that produced in the real world. However, the inference of results from an RCT can be restricted only to the kind of patients who were eligible for the RCT. In the real world, the clinician cannot exclude any patient from receiving treatment. Therefore, RCT results can have generalizability restrictions [
23,
24]. Real-world and observational studies are important to understand whether the benefits and efficacy of
S. boulardii CNCM I-745 seen in clinical trials are replicated in clinical practice. This real-world study, which was planned to evaluate the effectiveness of
S. boulardii CNCM I-745 in adult patients with diarrhoea, can help in bridging the gap between the clinical trial results and real-world practice.