From a clinical perspective, diarrhoea can be defined as the passage of:[1]World Health Organization. Health topics - diarrhoea. 2017 [internet publication].
http://www.who.int/topics/diarrhoea/en
[2]Riddle MS, DuPont HL, Connor BA. ACG clinical guideline: diagnosis, treatment, and prevention of acute diarrheal infections in adults. Am J Gastroenterol. 2016 May;111(5):602-22.
http://www.spg.pt/wp-content/uploads/2015/07/2016-acute-diarrhea.pdf
http://www.ncbi.nlm.nih.gov/pubmed/27068718?tool=bestpractice.com
Three or more loose or liquid stools per 24 hours, and/or
Stools that are more frequent than what is normal for the individual lasting <14 days, and/or
Stool weight greater than 200 g/day.
Based on duration, diarrhoea is classified as:[2]Riddle MS, DuPont HL, Connor BA. ACG clinical guideline: diagnosis, treatment, and prevention of acute diarrheal infections in adults. Am J Gastroenterol. 2016 May;111(5):602-22.
http://www.spg.pt/wp-content/uploads/2015/07/2016-acute-diarrhea.pdf
http://www.ncbi.nlm.nih.gov/pubmed/27068718?tool=bestpractice.com
[3]Arasaradnam RP, Brown S, Forbes A, et al. Guidelines for the investigation of chronic diarrhoea in adults: British Society of Gastroenterology, 3rd edition. Gut. 2018 Aug;67(8):1380-99.
https://gut.bmj.com/content/67/8/1380.long
http://www.ncbi.nlm.nih.gov/pubmed/29653941?tool=bestpractice.com
[4]World Gastroenterology Organisation. Acute diarrhea in adults and children: a global perspective. 2012 [internet publication].
http://www.worldgastroenterology.org/guidelines/global-guidelines/acute-diarrhea/acute-diarrhea-english
[5]Shane AL, Mody RK, Crump JA, et al. 2017 Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea. Clin Infect Dis. 2017 Nov 29;65(12):e45-80.
https://academic.oup.com/cid/article/65/12/e45/4557073
http://www.ncbi.nlm.nih.gov/pubmed/29053792?tool=bestpractice.com
Epidemiology
In the US, there are 375 million episodes of diarrhoea per year, of which 900,000 result in hospitalisations and 6000 in deaths. Worldwide, there are 2 billion episodes of diarrhoea per year, of which 1.9 million resulted in death among children <5 years.[4]World Gastroenterology Organisation. Acute diarrhea in adults and children: a global perspective. 2012 [internet publication].
http://www.worldgastroenterology.org/guidelines/global-guidelines/acute-diarrhea/acute-diarrhea-english
This makes it the second leading cause of death in post-neonatal children <5 years, after pneumonia.[6]Centers for Disease Control and Prevention. Global diarrhea burden. December 2015 [internet publication].
https://www.cdc.gov/healthywater/global/diarrhea-burden.html
[7]World Health Organization. Children: reducing mortality. October 2017 [internet publication].
http://www.who.int/mediacentre/factsheets/fs178/en
Implementation of improved access to oral rehydration therapy and education on feeding and weaning practices should help to reduce mortality from diarrhoeal disease, especially in the under-5 age group.[8]World Health Organization. World health statistics. 2008 [internet publication].
http://www.who.int/whosis/whostat/EN_WHS08_Full.pdf
Around 47.8 million cases of acute diarrhoeal infection occur each year in the US, with an estimated cost of at least US$150 million to the healthcare economy.[9]Scallan E, Griffin PM, Angulo FJ, et al. Foodborne illness acquired in the United States: unspecified agents. Emerg Infect Dis. 2011 Jan;17(1):16-22.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3204615
http://www.ncbi.nlm.nih.gov/pubmed/21192849?tool=bestpractice.com
[10]Scallan E, Hoekstra RM, Angulo FJ, et al. Foodborne illness acquired in the United States: major pathogens. Emerg Infect Dis. 2011 Jan;17(1):7-15.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3375761
http://www.ncbi.nlm.nih.gov/pubmed/21192848?tool=bestpractice.com
This compares to England and Wales, where infectious intestinal disease causes 300 deaths and 35,000 hospital admissions annually.[11]Wheeler JG, Sethi D, Cowden JM, et al; The Infectious Intestinal Disease Study Executive. Study of infectious intestinal disease in England: rates in the community, presenting to general practice, and reported to national surveillance. BMJ. 1999 Apr 17;318(7190):1046-50.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC27838
http://www.ncbi.nlm.nih.gov/pubmed/10205103?tool=bestpractice.com
There are an estimated 17 million cases and 1 million consultations with a general practitioner attributed to acute infectious diarrhoea in the United Kingdom every year.[12]Tam CC, Rodrigues LC, Viviani L, et al; IID2 Study Executive Committee. Longitudinal study of infectious intestinal disease in the UK (IID2 study): incidence in the community and presenting to general practice. Gut. 2012 Jan;61(1):69-77.
http://gut.bmj.com/content/61/1/69.long
http://www.ncbi.nlm.nih.gov/pubmed/21708822?tool=bestpractice.com
Basic pathophysiology
Normally approximately 10 litres of fluid consisting of ingested food and drink, in addition to secretions from the salivary glands, stomach, pancreas, bile ducts, and duodenum, enters the gastrointestinal tract every day. The small intestine is the major site for re-absorption. Overall, about 99% of the fluid is re-absorbed, leaving 0.1 litre to be excreted in the faeces. Diarrhoea occurs when various factors interfere with this normal process, resulting in decreased absorption or increased secretion of fluid and electrolytes, or increase in bowel motility.
Improved understanding of the pathophysiology of infectious diarrhoea, and the factors that promote the spread of causative infectious agents, will lead to practical approaches for preventing and responding to outbreaks.[13]Pawlowski SW, Warren CA, Guerrant R. Diagnosis and treatment of acute or persistent diarrhea. Gastroenterology. 2009 May;136(6):1874-86.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2723735
http://www.ncbi.nlm.nih.gov/pubmed/19457416?tool=bestpractice.com