Traveller’s Diarrhoea

Traveller’s diarhoea is the most common illness acquired overseas — affecting 20–50% of people travelling short-term from developed to developing regions.

It is caused by a wide range of pathogens — enterotoxigenic E. coli (ETEC) is the most common overall, but the mix depends on destination — Salmonella and Campylobacter are increasingly important causes in Asia, and norovirus dominates on cruise ships.

Severity — functional classification

The ISTM (International Society of Travel Medicine) defines severity by functional impact on the traveller’s activities, not stool frequency — this is the framework travellers should be given before departure so they know when to self-treat and when to escalate:

Severity	Definition	Self-management
Mild	Tolerable, not distressing, doesn’t interfere with planned activities	Rehydration ± loperamide
Moderate	Distressing or interferes with planned activities	Rehydration + loperamide or antibiotic
Severe	Incapacitating, prevents planned activities — all dysentery (grossly bloody stools) is severe by definition, regardless of stool frequency	Rehydration + antibiotic ± loperamide; seek medical help

Persistent diarrhoea = ≥2 weeks.

Pathogen	% of traveller’s diarrhoea	Usual incubation	Duration
Enterotoxigenic E. coli	~15%	12–72 hours	3–5 days
Campylobacter jejuni	~10%	1–7 days	2–10 days
Salmonella enterica	Common	6–72 hours	2–7 days
Shigella spp.	~5%	12 hours – 7 days	2–5 days
Norovirus	Predominant on cruise ships	12–48 hours	1–3 days
Rotavirus	Uncommon in adults	1–3 days	3–8 days
Giardia duodenalis	1–5%	1–3 weeks	Weeks to months (can be prolonged)
Entamoeba histolytica	Uncommon	2–4 weeks	Weeks to months
Cryptosporidium spp.	Uncommon	~1 week	Can be prolonged, especially in children/immunocompromise

Clinical clues to aetiology

Presentation	Think of
Few, voluminous, watery stools (severe in cholera; pale/fatty/smelly in giardiasis)	Small-bowel process: V. cholerae, ETEC, early shigellosis, giardiasis
Many small-volume stools, tenesmus, dysentery	Large-bowel process: Shigella, Salmonella, Campylobacter, diarrhoeagenic E. coli, Yersinia
Predominant vomiting	Viral (rotavirus, calicivirus, norovirus) or toxin-mediated (e.g. S. aureus)
Predominant fever	Shigella, Salmonella (esp. enteric fever), Campylobacter, viral agents, EHEC
Prolonged diarrhoea (weeks)	Giardia, E. histolytica, Cryptosporidium

Prevention

• Freshly cooked, steaming-hot food; fruit that can be peeled; bottled/canned/ recently-boiled beverages.
• Avoid raw/undercooked meat or seafood, fresh salads, unpasteurised dairy, unboiled water, ice, and roadside-vendor food (often the highest-risk source).
• Contamination routes are easy to overlook: travellers who avoid drinking local water can still be infected by brushing their teeth with an improperly-rinsed toothbrush, drinking a bottled drink with ice made from local water, or eating food washed with local water.
• People taking medications that decrease stomach acid — antacids, H2 blockers, and proton pump inhibitors — are at risk of more severe illness, since gastric acid is itself part of the body’s normal defence against ingested pathogens.
• Stand-by self-treatment is preferred over antibiotic prophylaxis for most travellers (including children) — prophylaxis carries a real risk of driving antimicrobial resistance.
• Prophylaxis can be considered for those at risk of severe disease (e.g. immunocompromised) but should not continue beyond 3 weeks; check local resistance data (quinolone resistance is rising in many regions). Patients with inflammatory bowel disease, HIV, an organ transplant, or severe cardiovascular or kidney disease are the specific higher-risk groups international guidance targets for prophylaxis; rifaximin (non-absorbed) is the preferred agent for this, and fluoroquinolones specifically are not recommended for prophylaxis given their adverse-effect profile (tendon rupture, peripheral neuropathy) — a stronger caution than simply avoiding them for resistance reasons alone.
• The cholera vaccine currently available has insufficient evidence of protection against ETEC-related traveller’s diarrhoea and is not licensed in Australia for this indication (TravelHealthPro similarly describes only limited” ETEC cross-protection from the UK’s Dukoral, not a licensed indication). “A 2013 Cochrane review of 24 randomised controlled trials found no statistically significant effect of the currently-available Dukoral formulation on ETEC diarrhoea, based on a single trial of travellers from the USA to Mexico; an earlier, no-longer-available precursor vaccine did show short-term protection lasting around 3 months in two other trials, but no ETEC-specific vaccine in development has yet demonstrated a clinically important benefit either.

Treatment

Mild disease — self-limiting; rehydration is the mainstay. Antimotility drugs can be considered in adults but should not be used in children. Loperamide dosing: 4 mg initial dose, then 2 mg after each further loose stool, to a maximum 16 mg/24 hours; not used under 2 years of age. Antibiotics are not recommended for mild disease (ISTM: strong recommendation) — the risk of antimicrobial resistance and adverse effects outweighs the modest symptom benefit in illness that isn’t disrupting the trip.

Bismuth subsalicylate (Pepto-Bismol) is a recognised alternative to loperamide internationally (ISTM), but isn’t specifically addressed by the Australian eTG guideline and isn’t in routine local use for this indication.

Moderate–severe disease — rehydration remains essential (critical in young children). Antibiotics are effective and stand-by self-treatment is generally appropriate. A single large dose usually suffices; use a longer course if fever or bloody stools are present:

Drug	Single-dose option	If fever/bloody stools, or no improvement — continue with
Azithromycin	1 g (child: 20 mg/kg up to 1 g) PO once	500 mg (child: 10 mg/kg up to 500 mg) PO daily for 2 more days
Norfloxacin	800 mg (child: 20 mg/kg up to 800 mg) PO once	400 mg (child: 10 mg/kg up to 400 mg) PO 12-hourly for 2 more days
Ciprofloxacin	750 mg (child: 20 mg/kg up to 750 mg) PO once	500 mg (child: 12.5 mg/kg up to 500 mg) PO 12-hourly for 2 more days

Antimotility drugs can be combined with antibiotics in adults without fever or bloody stools. Quinolone resistance is emerging in Gram-negative pathogens, particularly South Asia — factor this into first-line choice (azithromycin is generally preferred where resistance is a concern).

Antibiotic treatment itself (not just prophylaxis) carries a real risk of subsequent colonisation with multidrug-resistant/ESBL-producing organisms — a single-dose regimen where clinically appropriate helps minimise this. Rifaximin (a non-absorbed antibiotic) is a recommended alternative for non-invasive traveller’s diarrhoea in international guidelines (ISTM, CDC) but is not included in the Australian eTG traveller’s diarrhoea guideline and isn’t in routine local use for this indication — it’s ineffective against invasive pathogens (Campylobacter, Salmonella, Shigella), so shouldn’t be used for dysentery or febrile diarrhoea regardless.

Persistent diarrhoea in the returned traveller

Consider both infective (giardiasis, amoebiasis, and Clostridioides difficile if there’s been recent antibiotic exposure) and non-infective causes (post-infectious IBS, lactose intolerance, coeliac disease) — a detailed travel and exposure history gives useful clues.

• Stool microscopy and culture (multiple samples may be needed for some parasites, particularly those not identified by multiplex PCR testing); serology can help for amoebiasis, schistosomiasis, strongyloidiasis.
• A cause isn’t identified in a large proportion of cases — many patients develop post-infectious IBS.
• If no cause is found, a trial of empirical giardiasis treatment can be considered; seek expert advice if symptoms persist.

Giardiasis — asymptomatic carriage in immunocompetent patients usually doesn’t need treatment. For symptomatic patients:

Drug	Regimen
Tinidazole	2 g (child: 50 mg/kg up to 2 g) PO once
Metronidazole	2 g (child: 30 mg/kg up to 2 g) PO daily for 3 days, or 400 mg (child: 10 mg/kg up to 400 mg) PO 8-hourly for 5 days