In Nepal, you better keep your mouth shut when you take a shower.

You may be in the fanciest hotel in Kathmandu, but if the water touches your lips, prepare to postpone your trekking trip in the Himalayas, because there's a risk you’ll soon be crouching on the bathroom floor, hugging the toilet. This is the advice given in most guidebooks, because water in Nepal is contaminated with tiny parasites called Giardia intestinalis. If ingested, they can cause diarrhoea, vomiting, abdominal cramps, nausea, bloating and fever.

“Travellers’ diarrhoea is the most predictable travel-related illness,” says Ian Branam of the Centers for Disease Control and Prevention, the US’s leading national public health institute. Every year, anywhere between three and seven out of 10 travellers get it, depending on their destination and season of travel. According to research at Fleet Street Clinic, a travel clinic in London, more than 50 million Western travellers succumb to the illness, and almost 40% require medical attention.

How you travel doesn't really matter, although there are some risks that can be identified, says Richard Dawood, a travel doctor at Fleet Street Clinic. “For example, on one’s journey through an airport – getting there by public transport, going through security and perhaps handling one’s own shoes, hanging on to handrails in a bus to the aircraft, and so on – they can then become quite a risk attached to eating a meal without washing one’s hands,” he says.

As unpleasant as it may be, norovirus isn’t the worst offender. In high-risk regions, only 10% of the infectious agents in food are norovirus; that’s even less than parasites such as entamoeba (amoebic dysentery) or giardia; causing about four-fifths of the tummy upsets and worse are bacteria, says Robert Steffen, an infectious diseases specialist at the University of Zurich.

The largest contributor is poor hygiene in local restaurants

It’s often unclear just what causes travellers’ diarrhoea, says Steffen, but there is typically a clear course of action. He recalls that recently – after attending a conference on travel medicine in Port Elizabeth, South Africa – he was watching primates in a nature reserve, when he encountered “a British gentleman” who was clearly unwell and dehydrated because of travellers’ diarrhoea. He was already taking Imodium, but for any patient “it is far more important to look forward,” says Steffen. On the walk in the hills he urged the man to drink plenty of water. Upon return to the lodge, the manager prepared him an oral rehydration solution. Since he planned to board several flights to return home within 24 hours, Steffen recommended he take an antibiotic from his travel kit. Fortunately, he says, “he felt far better the next morning and was able to return as planned”.

So why is it that in some areas travellers run a great risk in getting ill? The largest contributor to travellers’ diarrhoea, says Branam, is poor hygiene in local restaurants. The illness is also more common in young adult travellers than older travellers, “but that’s probably due to them being more adventurous eaters than due to age or biology”, he adds.

It can feel very unfair if one succumbs to a bug at the start of a two-week holiday, while the locals eating at the same restaurants are doing just fine. That’s because you’re suddenly exposed to new, previously unencountered intestinal pathogens to which you’ve not yet acquired immunity, says Kurt Hanevik, a clinician at the University of Bergen in Norway. Another reason is rushed eating, adds Glenn Gibson from Reading University, which often is preceded by “rushed preparation of the food”.

It's important to distinguish travellers’ diarrhoea and food poisoning. The latter is the result of eating toxins that have already formed in the food, and while it may cause both vomiting and diarrhoea, it’s usually over within 12 hours, says Braman.

So what should you do if you’re planning to travel to a high-risk area? Steffen advises bluntly: “No sashimi in Kathmandu, no ice cream from the street or beach vendors in Goa.” But otherwise, he adds, there is no real evidence that the old rule “boil it, cook it, peel it — or forget it” would be of significant benefit, as the risk for travellers’ diarrhoea won’t be completely eliminated no matter what you do. So beyond avoiding uncooked or poorly cooked food and all buffet meals, you can reduce the risk by cleaning your hands regularly with an alcohol-based hand sanitizer (containing more than 60% alcohol), putting iodine drops in Giardia-prone tap water – if no bottled or filtered water is available – and definitely opting out of ice cubes in drinks.

Researchers have also looked into vaccination, but so far it has been shown to have minimal effectiveness

Glenn Gibson from Reading University advises to take probiotics and prebiotics as prophylactic treatment – to keep infection at bay. Probiotics, dubbed ‘friendly bacteria,’ are living microorganisms that, when ingested, are thought to help digestion and improve your defences against possible infection. Prebiotics are substances, typically fibre-based, that promote the growth of beneficial microorganisms in the digestive system. 

Probiotics are found naturally in fermented foods such as live (bio) yogurts and cheeses, miso soup, sourdough bread and sauerkraut. There are also probiotics supplements, capsules, yogurt shots and drinks, containing a lot of friendly bacteria. “They are harmless, and can inhibit or repress the microbes that cause gastroenteritis,” says Gibson.

But not everyone agrees. According to a recent study, prophylactic probiotics Lactobacillus didn’t have much effect on cutting the risk of travellers’ diarrhoea. Prebiotics, on the other hand, do seem to increase resistance to infection and diarrhoeal disease; one placebo-controlled study of a daily sachet of galacto-oligosaccharide mixture showed a 36% reduction in occurrence of travellers’ diarrhoea.

Apart from pro and prebiotics, there are also prophylactic antibiotics that one can take – but the danger is they won’t do anything against a viral or parasitic infection, and it’s not recommended to take too many antibiotics because it can result in bacteria developing antibiotic resistance. Researchers have also looked into vaccination, but so far it has been shown to have minimal effectiveness.

Traditionally, if you get ill, you should have your stool culture examined in the lab to identify the root cause. That’s because parasites, viruses and bacteria can cause similar symptoms but need different approaches for successful treatment. Delaying treatment is not a good idea – a study showed that people who had serious Giardia infection were much more likely to develop irritable bowel syndrome and chronic fatigue six years after originally falling ill.

Next time you travel, research first how likely you are to get traveller’s diarrhoea in the area you’re going to

But these methods are prone to error, take days, are not always available to travellers, and lead to delays in starting the right treatment. Patients that have enough time to wait for results must take rehydration drinks, and may want to resort to antimotility agents such as Imodium to deal with diarrhoea. They even may, blind-guessing, turn to antibiotics.

The traditional tests are also pretty useless as they cannot detect the most frequent pathogens, says Steffen.

A much more modern approach is PCR (Polymerase Chain Reaction) detection in stool samples, which tries to identify the tiniest traces of genetic material from the viruses, bacteria and parasites that cause infection. At the Fleet Street Clinic in London, for example, clients are given cotton bud-sized containers as part of their medical kits before they go on their travels. This way, they can send stool samples home by courier. The clinic says it can detect any of the 22 most common pathogens that cause diarrhoea, from norovirus and rotavirus, to bacteria like E. coli, salmonella, campylobacter and shigella (bacterial dysentery), to parasites like giardia and entamoeba.

Of course if you are trekking in the Himalayas, going to a clinic or sending anything back home is out of the question. In that case, you’d have to rely on your own medication kit.

Most importantly, next time you travel, research first how likely you are to get traveller’s diarrhoea in the area you’re going to. And don’t avoid the busy, colourful and amazing streets of Kathmandu and the stunning landscapes of the Himalayas just because of a possibility of getting sick; just make sure you shower with your mouth firmly shut.

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