Aetiology

An estimated 80% to 90% of cases are caused by the ingestion of bacterially contaminated food or water.[2]​ Common bacterial culprits include enterotoxigenic Escherichia coli, enteroaggregative E coli, Shigella, Campylobacter jejuni, and Salmonella (non-typhoid species). Less common causative organisms include Yersinia, Vibrio (non-cholera species), Aeromonas, and Plesiomonas shigelloides.

E coli is the most common pathogen, especially in Latin America. Campylobacter infections are most prevalent in South and Southeast Asia, where TD may involve more invasive (and drug-resistant) organisms.[4][15]​​​​[16][17][18]​​​​​​

Viruses account for at least 5% to 15% of infections, whereas protozoal pathogens account for about 10% of infections.[2]​ TD of viral aetiology includes rotavirus in children, norovirus (typically affecting people on cruise ships), astrovirus, sapovirus, and other enteric viruses.[2]​

Persistent diarrhoea (lasting >14 days) may be of parasitic origin and may be caused by Giardia, Entamoeba, Cryptosporidium, Dientamoeba, or Cyclospora.

Self-limited post-infectious irritable bowel syndrome affects approximately 5% of returning travellers and may cause persistent diarrhoea.​[4]​​[5][6][7]​​​​

Pathophysiology

Bacteria in food or water may readily survive passage through the stomach resulting in an enteric infection with cramping and diarrhoea. Incubation period and progress of infection depend on the causative microbial agent.[19]​ For some bacteria, such as Shigella, only a minute inoculum is sufficient, while for others, such as Salmonella, many organisms are required. More invasive bacterial infections damage the mucosal lining and produce dysentery (bloody stools), usually with systemic symptoms such as fever.

Four strains of enterovirulent Escherichia coli are associated with TD:

  • Enterotoxigenic (the principal cause of TD)

  • Enteroaggregative (the second most common cause of TD)

  • Enteroinvasive (causing a Shigella-like dysentery)

  • Enteropathogenic (causing infant diarrhoea).

Enterotoxigenic E coli produces two toxins, a heat-stable toxin and a heat-labile toxin, both of which cause diarrhoea by increasing intestinal fluid secretion. A heavy inoculum (>10 million organisms) produces diarrhoea in about 24 hours.[20]

A fifth strain of E coli, enterohemorrhagical (E coli O157:H7) causes haemolytic uraemic syndrome in childhood. Although caused by contaminated food, it is very rarely associated with travel.

Classification

Clinical entities[1]

  • Mild (acute): diarrhoea that is tolerable, is not distressing, and does not interfere with planned activities.

  • Moderate (acute): diarrhoea that is distressing or interferes with planned activities.

  • Severe (acute): diarrhoea that is incapacitating or completely prevents planned activities; all dysentery (passage of grossly bloody stools) is considered severe.

  • Persistent: diarrhoea lasting >14 days.

Aetiological entities

  • Bacterial traveller's diarrhoea: common infection usually due to enterotoxigenic Escherichia coli (ETEC) and enteroaggregative E coli, Shigella, Salmonella (non-typhoid), Campylobacter jejuni. Less common causative organisms include Yersinia, Aeromonas hydrophila, Plesiomonas shigelloides, and Vibrio (non-cholera) species.

  • Viral traveller's diarrhoea: diarrhoea due to rotavirus (especially in infants and children), norovirus (e.g., on cruise ships), astrovirus, and other enteric viral infections, notably sapovirus.

  • Parasitic traveller's diarrhoea: more persistent (>14 days) diarrhoea due to parasitic infection with Giardia, Entamoeba, or Cryptosporidium.

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