Introduction

Traveller’s Diarrhoea (TD) is a common gastrointestinal disorder in travellers from industrialized countries to developing countries where there is poor public sanitation, and this occurs within the first 10 days of their visit.¹ It is defined by the passage of unformed stools and is usually associated with abdominal cramps, nausea, fever, and bloating. This condition is considered one of the most common illnesses experienced by travellers, especially those visiting a place that has a different climate or hygiene standards than they are accustomed to.² TD normally resolves spontaneously in a few days without treatment; however, in some instances, it can produce serious complications, particularly in high-risk groups - these include young children, the elderly, or individuals who are immunocompromised.^{2 5 6}

Each year, millions of international travellers experience traveller’s diarrhoea, infecting about 30-60% of travelers to high-risk locations, particularly regions of South Asia, sub-Saharan Africa, and Latin America.^{1 2 3 4} Contaminated food, poor sanitation, and unsafe water are the main culprits for the prevalence of TD.⁶ However, based on the destination, personal hygiene practices, and dietary intake during travel, the risk of acquiring TD may vary.

The typical causative agents of Traveller's Diarrhoea are parasites, viruses, or bacteria.¹ These are typically acquired by ingestion of food or water that contains faecal organisms. 

• Bacteria are the most frequent cause of Traveller's Diarrhoea.^1,2  Enterotoxigenic Escherichia coli (ETEC) is the most prevalent bacterial cause and has been calculated to be responsible for approximately 30% to 50% of cases. The other frequent bacterial causes include Campylobacter jejuni, Shigella, and Salmonella species^{4 5} 
• Viruses are a rare cause of Traveller's Diarrhoea among the bacteria.¹ The most common viral cause is Norovirus, with rotavirus being another source of viruses that cause the infection⁴
• Parasites are another reason behind Traveller's Diarrhoea, though not as common as bacteria. The most common parasitic origin is Giardia intestinalis. Cryptosporidium and Entamoeba histolytica are other parasites that can result in this condition

Pathophysiology of traveler’s diarrhea

Mechanisms of infection and toxin production

Traveller's diarrhoea is largely the result of ingestion of food or water that has infectious pathogens, generally bacteria but sometimes viruses or parasites.¹ The primary mode of transmission is faecal-oral.⁴ The most common bacterial cause is enterotoxigenic Escherichia coli (ETEC), estimated to be responsible for approximately 30% of the cases. This releases enterotoxins that cause profuse fluid and electrolyte secretion into the intestinal lumen, causing watery diarrhoea.²  The other commonly implicated bacteria are Campylobacter jejuni, Shigella, and Salmonella species, which invade intestinal epithelial cells, causing inflammation and tissue damage, resulting in dysentery.⁴ Viral etiologies like Norovirus and rotavirus, and parasitic etiologies like Giardia intestinalis, Cryptosporidium, and Entamoeba histolytica. The incubation period, which is the time from exposure to the onset of symptoms, varies by the specific causative agent. 

Effect on the gastrointestinal tract

The pathophysiology of traveller's diarrhoea can be broadly categorised into non-inflammatory and inflammatory mechanisms, depending on the type of causative organism.⁴ The body’s gastrointestinal system fights against non-inflammatory agents that tend to diminish the absorptive activity of the intestinal mucosa by developing peristalsis and mucus secretion, leading to increased output of the gastrointestinal tract, expelling the pathogen but at the expense of diarrhoea.^1,4 On the other hand, inflammatory drugs either lyse the lining of the intestine by releasing cytotoxins or by invading the mucosa itself.⁴ In worse instances, widespread inflammation inflicts damage on the intestinal mucosa, leading to chronic malabsorption and nutrient deficiency.⁶

Immune system response

The immune response plays a critical role in the control of TD. The mucosal IgA secretory in the gut serves as the first line of defence, followed by systemic immune mechanisms to eliminate the infection.³ In the immunocompromised hosts, however, inefficient immune mechanisms can lead to chronic infection and complications such as bacteremia.⁴

Common symptoms and clinical course

Mild to moderate diarrhoea

The characteristic symptom of TD is the acute development of loose or watery stools, usually occurring three or more times a day. The condition ranges from mild to moderate cases, which generally subside on their own.¹

Abdominal cramping, nausea, vomiting

The majority of the travellers experience abdominal cramps as a consequence of increased intestinal motility and inflammation. Nausea and vomiting are more common in viral infection cases, such as norovirus.²

Fever and dehydration

Invasive bacterial infections by Shigella spp. and Salmonella spp often accompany fever and systemic symptoms. One of the major complications is dehydration caused by an excess of body fluids, which may be life-threatening, especially in very young children and the elderly.⁴

Complications of traveler’s diarrhoea

Dehydration and electrolyte imbalance⁴

Risk factors for severe dehydration

Recurrent, watery stools can lead to significant fluid and electrolyte loss. Dehydration can be mild, moderate, or severe and life-threatening in young children, the elderly, and patients with chronic diseases.⁶ Fluid and electrolyte loss can lead to hypotension, tachycardia, and shock. 

Signs and symptoms (dry mucous membranes, hypotension, tachycardia)

• Dry mouth and mucous membranes²
• Decreased urine output
• Intense thirst
• Dizziness or lightheadedness
• Rapid heart rate (tachycardia)
• Sunken eyes

Management and prevention strategies

Fluid repletion is the basis for managing diarrhoea.

• Oral Rehydration Therapy (ORT): Oral Rehydration Therapy, as supported by the World Health Organisation, employs solutions that have particular proportions of salts and sugars for maximum absorption. These involve consuming sports drinks with electrolyte fluids and Pedialyte.
• Intravenous Fluids: For instances of severe dehydration where oral intake is not feasible or adequate, intravenous rehydration and oral rehydration salts may be required.

Persistent or chronic diarrhea

Prolonged infection due to protozoa 

Although most TD symptoms persist for only a few days to a week, some patients experience prolonged or chronic diarrhoea.¹  Prolonged diarrhoea that lasts for weeks to months can be the consequence of protozoal infections such as Giardia lamblia and Cryptosporidium spp.⁴,⁵ These infections typically lead to malabsorption and weight loss.

Post-infectious irritable bowel syndrome (PI-IBS)

Few people with traveller's diarrhoea go on to develop postinfectious irritable bowel syndrome (PI-IBS).¹ It may manifest with chronic diarrhoea, cramping and pain in the abdomen, and bloating.¹ The correlation between traveller's diarrhoea and the subsequent development of irritable bowel syndrome (IBS) exists, with up to 50% reported incidences.⁴ 

Diagnostic approaches and treatment

In most instances of traveller's diarrhoea, laboratory testing is not typically required. Stool tests can be taken, however, in patients with alarming features like high fever, bloody stool, or prolonged symptoms. These tests are sometimes done and consist of:

• Stool culture: To check for bacteria, viruses, and parasites^{1 4}
• Faecal leukocytes and lactoferrin: To check for inflammatory causes⁴
• Ova and parasite testing: This is done in patients with symptoms lasting longer⁴
• New multiplex polymerase chain reaction (PCR) tests: These are being developed to screen several stool pathogens rapidly, although they are not always likely to change clinical management⁴

Secondary infections and sepsis

Risk of bacteremia in immunocompromised individuals

In immunocompromised patients, TD pathogens can penetrate the bloodstream, leading to bacteremia and sepsis.⁴ The risk is particularly high in elderly patients, HIV/AIDS patients, and those undergoing chemotherapy.

Spread of infection beyond the gut

Certain bacterial pathogens, such as Salmonella and Shigella, can extend beyond the intestines and infect organs such as the liver, spleen, and central nervous system.⁵ 

Importance of early detection and intervention

Early diagnosis and antibiotic treatment are extremely significant in preventing severe effects. In immunocompromised individuals, empirical antibiotic therapy may be necessary to prevent complications.²

Malabsorption and nutritional deficiencies

Impact of chronic diarrhoea on nutrient absorption

Chronic diarrhoea may interfere with the absorption of necessary nutrients, leading to malnutrition and weight loss.³ 

Risk factors for deficiencies 

Iron, vitamin B12, and fat-soluble vitamins (A, D, E, and K) deficiency caused by TD malabsorption can lead to anaemia, neurological disease, and compromised immunity.⁶

Long-term consequences and dietary management

Chronic malabsorption may lead to repeated gastrointestinal symptoms and failure to thrive in the patient. Nutritional rehabilitation, through supplementation with vitamins and diet change, is paramount to healing.⁴

Prevention strategies

Hygiene and food safety measures

Practices of food safety and hygiene form the cornerstone of traveller's diarrhoea prevention. In order to successfully reduce your risk, you need to be extremely cautious regarding what you consume and how you maintain hygiene. For example:

• Use only boiled water or chemically disinfected bottled water for all purposes, such as drinking, preparing beverages, ice, tooth brushing, and washing hands and food¹
• Do not use tap water or ice, and if in doubt, treat the water by boiling it for three minutes or by using a filter or chemicals like iodine or chlorine³ 
• Ensure that meat, fish, and shellfish are properly cooked, and be careful with moist foods left at room temperature² 
• Opt for fruits and vegetables you can peel yourself. Salads and non-peelable fruits are to be avoided⁴
• Wash hands with soap and water regularly, especially before eating and after going to the toilet, and apply an alcohol-based hand gel if hand washing is not feasible¹

Vaccination options 

Vaccination against Vibrio cholerae and enterotoxigenic Escherichia coli (ETEC) provides protection against TD.^3,4 Whereas these vaccines are not universally administered, they may be beneficial for those who are at higher risk of exposure.

Prophylactic antibiotics and probiotics

Prophylactic antibiotics such as azithromycin or rifaximin may be administered to high-risk travellers to protect them from TD.⁴  However, routine prophylaxis should be avoided due to the risk of antibiotic resistance. Probiotics containing Lactobacillus and Saccharomyces boulardii may be administered to enhance gut microbiota equilibrium and to reduce the incidence of TD.⁵ 

Summary

Traveller's diarrhoea, which is normally a self-limiting and trivial illness, can have a variety of potential complications that are severe, including fluid and electrolyte loss with resulting dehydration, especially in vulnerable populations.²,^4,5,6 A serious long-term complication is post-infectious irritable bowel syndrome (PI-IBS), characterised by chronic gastrointestinal symptoms. In severe situations, especially in immunocompromised hosts, the infection can cause sepsis, a systemic and potentially fatal reaction.

Early diagnosis and appropriate treatment are therefore essential; travellers should be educated on recognising severe signs such as fever, bloody diarrhoea, persistent vomiting, or dehydration and presenting for urgent medical attention.¹ Physician experts must obtain careful travel histories and order stool tests for chronic or severe presentations, guiding therapy with fluid resuscitation and careful use of antibiotics, without routine prophylactic antibiotic therapy.⁴ Preventive measures for travellers include rigid food and water safety protocols and proper hand hygiene, and medical practitioners have a valuable role to play in educating their patients on these interventions and the resulting complications.¹