Food and Water Safety When Travelling: The Clinical Detail Behind the Advice Travellers Are Usually Given

Almost everyone heading abroad has heard some version of the same advice: don’t drink tap water, avoid ice, be careful with salads. It is the standard refrain of the travel health consultation, and it is not wrong. But it is incomplete, and incomplete advice tends to produce a kind of selective vigilance that misses important risks while providing false reassurance about others.

As a pharmacist working in travel health at Priory Pharmacy in York, I have found that patients who understand the actual mechanisms of travel-related gastrointestinal illness make better decisions than those who have simply been given a list of things to avoid. The biology of foodborne illness while travelling is more interesting, and more clinically informative, than ‘don’t eat street food.’

Understanding Traveller’s Diarrhoea: Causes and Mechanisms

Traveller’s diarrhoea (TD) is defined as three or more unformed stools in 24 hours in a traveller to a high-risk destination, typically accompanied by at least one additional symptom such as nausea, vomiting, abdominal cramps, fever or urgency. It is the most common travel-related illness, affecting between 20 and 60 percent of travellers to South Asia, sub-Saharan Africa, Latin America and parts of the Middle East, depending on destination, duration and individual behaviour.

The causative agents are predominantly bacterial. Enterotoxigenic Escherichia coli (ETEC) is the most common pathogen identified in most destinations, responsible for approximately 30 to 40 percent of cases. It produces heat-labile and heat-stable enterotoxins that stimulate intestinal fluid secretion, producing the watery diarrhoea characteristic of most TD episodes. Other important bacterial causes include Campylobacter jejuni (particularly prevalent in Southeast Asia), Salmonella species, Shigella species and enteroaggregative E. coli (EAEC).

Viral causes, predominantly norovirus and rotavirus, account for a smaller proportion of TD cases but are responsible for the highly infectious outbreaks that are disproportionately reported from cruise ships, where shared enclosed spaces and dense catering operations create ideal transmission conditions. Protozoal infections including Giardia lamblia and Cryptosporidium are less common causes of acute TD but are important in the context of persistent post-travel diarrhoea lasting more than two weeks.

The Transmission Routes That Matter Most

The Faecal-Oral Route: More Routes Than Most Travellers Realise

The primary transmission route for most TD pathogens is faecal-oral, ingestion of organisms shed in human or animal faeces. What this means in practice is broader than most travellers appreciate. The faecal-oral route encompasses not only contaminated water, but any food or surface that has come into contact with contaminated water or inadequately washed hands during preparation.

This is why the simple instruction to ‘avoid salads’ understates the actual risk pathway. Raw vegetables washed in contaminated water carry the same organisms as the water itself. Ice made from contaminated water is just as hazardous as drinking that water directly. A freshly cooked meal served on a plate rinsed in contaminated water, or handled by someone who did not wash their hands adequately, represents a transmission route that hygiene-focused behaviour after ordering cannot address.

High-Risk Foods: The Evidence Base

The foods most consistently associated with TD transmission in epidemiological studies are those that cannot be adequately heat-treated before consumption, or that have significant potential for post-cooking contamination. The highest-risk categories are:

• Raw or undercooked shellfish, filter feeders that concentrate pathogens from contaminated water, including hepatitis A virus, norovirus and Vibrio species
• Raw leafy vegetables and salads, difficult to decontaminate by washing and often irrigated with untreated water in high-risk destinations
• Unpasteurised dairy products, milk, cheese and yoghurt from unverified sources carry Campylobacter, Salmonella, Brucella and other pathogens
• Cold buffet foods, cooked foods left at ambient temperature for extended periods allow bacterial multiplication to infective doses
• Ice and ice cream from unverified sources, frozen water does not kill pathogens; it preserves them
• Street food that has been prepared and then kept warm rather than freshly cooked, the distinction between ‘freshly cooked to order’ and ‘kept hot’ is clinically significant

Lower-Risk Foods: Understanding Why

The principle underlying food safety advice is straightforward: adequate heat kills most pathogens. Foods that are freshly cooked to a high internal temperature (above 70°C) and consumed immediately represent substantially lower risk, including street food, which is consistently maligned in generic travel advice but is often safer than hotel buffet food that has been sitting in warming trays for hours.

Fruits that can be peeled by the traveller themselves are generally safe, the peel provides a sterile barrier between the contaminated outer surface and the edible flesh. Bottled water from sealed bottles with intact tamper-evident caps, carbonated drinks in sealed cans or bottles, and hot beverages made with boiling water (though note that at high altitude, water boils below 100°C) are safe choices.

Water Purification When Bottled Water Is Unavailable

In remote destinations or situations where commercially bottled water is not reliably available, travellers should understand the options for water treatment and their relative effectiveness:

Handwashing: The Most Consistently Undervalued Intervention

The evidence for handwashing with soap as a TD prevention strategy is strong and consistent, and yet it remains the intervention most readily abandoned when hand-washing facilities are inconvenient, which in travel settings is frequently. Alcohol-based hand sanitisers (at least 60 percent alcohol) are effective against most bacterial and viral TD pathogens and are highly practical for travel use. They are not effective against Cryptosporidium oocysts or Clostridium difficile spores, but for the majority of TD pathogens encountered by most travellers, they represent a highly effective and accessible preventive measure.

The critical handwashing moments are before eating, before food preparation and after using the toilet. These are well known. Less often emphasised is handwashing after handling cash, which is often heavily contaminated with faecal organisms in high-risk destinations, and after any contact with animals, which are reservoirs for Campylobacter and Salmonella in particular.

When and How to Treat Traveller’s Diarrhoea

Most episodes of TD are self-limiting, resolving within three to five days without antibiotic treatment. The primary clinical priority is preventing dehydration through adequate oral rehydration. Commercial oral rehydration salts (ORS) are the most effective hydration strategy, they exploit the intestinal sodium-glucose co-transporter mechanism that remains intact even in secretory diarrhoea, enabling fluid absorption even when gut motility is impaired. Sports drinks and fruit juices are not adequate substitutes.

Loperamide (an antimotility agent) can be used to reduce stool frequency and allow travellers to function, for example, on a long-haul flight or in a situation where toilet access is limited, but it does not treat the underlying infection and is contraindicated in bloody diarrhoea or when invasive bacterial infection is suspected (fever, blood in stool, severe systemic symptoms).

This article is for general information purposes and does not constitute individual clinical advice. For personalised travel health advice before your trip, please book a travel consultation at Priory Pharmacy in York.