Traveller's diarrhoea in Vietnam: what actually helps, and what to stop doing

This is the illness most likely to interrupt your trip, and it is worth reading before it happens rather than at four in the morning on a bathroom floor in a guesthouse you booked yesterday.

The short version: drink properly, stop counting, and watch for two things — blood and fever. Everything below is the detail behind that sentence.

It happens to careful people

Somewhere between 30% and 70% of travellers develop diarrhoea during a two-week trip, depending on the destination and the season. It is the most predictable travel illness there is. It is not a weak stomach and it is not bad luck.

You have probably met the rule — boil it, cook it, peel it, or forget it. It is not useless, but people who follow it still get ill. The dominant factor is not the ice in your drink; it is hygiene in a kitchen you never see: how hands are washed, whether the fridge held temperature through an afternoon power cut, what the chopping board touched before your food did.

That is worth knowing, because the alternative is spending a holiday suspicious of every meal and getting ill anyway. Eat sensibly, then stop auditing yourself.

The gap between the meal and the symptoms tells you a lot

How long it took is the single most useful thing you can work out on your own.

• A few hours — usually a toxin already present in the food. Short, violent, then over.
• Six hours to four days — usually bacteria or a virus. Bacterial cases run about three to seven days untreated; viral ones about two to three, with more vomiting.
• One to two weeks — this is the timescale of a parasite, which can persist for weeks or months if it is not treated.

Bacteria account for most cases — roughly 75% to 90%. Viruses make up another 10% to 25%. Parasites are about one case in ten and show up mostly in people who have been travelling for months rather than a fortnight.

So: ill the same evening as a specific meal, and it probably was that meal. Ill on day three, and you can stop interrogating your travel companion about where they had lunch.

Stop counting trips to the toilet

Most advice online tells you to count. Current guidance dropped that years ago and replaced it with a better question: has this stopped you doing things?

• Mild — unpleasant, but your day still happened. No antibiotics. Fluids, and loperamide if you have a bus to sit on.
• Moderate — distressing, or it wrecked the day. Antibiotics become a reasonable option, and which one is a decision for a clinician who has examined you.
• Severe — you cannot function. Any blood in the stool counts as severe automatically. You want someone qualified looking at you.

This scale is better because it matches how you actually experience it. Nobody counts. Everybody knows whether they cancelled the day.

One caution about loperamide, the anti-diarrhoeal most people carry: it is genuinely useful for a mild case or a long journey. Do not take it on its own if you have blood in your stool or a fever. Slowing everything down while an invasive infection is present is the wrong move.

Red flags — do not wait for a doctor to travel to you

Call 115 or go straight to the nearest emergency department if any of these are true:

• You are vomiting blood, or the vomit looks like ground coffee
• Your skin, lips or tongue turn blue, grey, pale or blotchy
• You are struggling to breathe
• You are confused, or cannot be kept awake
• There is severe pain fixed in one part of the abdomen

Same-day review, but not an emergency

• You still look dehydrated after using rehydration sachets
• You cannot keep any fluid down at all
• There is blood in your stool
• Diarrhoea has run past seven days, or vomiting past two
• You are pregnant, elderly, travelling with a young child, or living with a long-term condition — the threshold for being seen is much lower
• Signs of dehydration: dizziness, cramps, sunken eyes, very little urine, a dry mouth, weakness, a fast heartbeat

The rehydration part almost everyone gets wrong

This is the thing that matters most in the first twenty-four hours, and the thing most people do badly — usually by reaching for whatever is coldest and sweetest in the hotel fridge.

• If you are losing a lot of fluid, use proper oral rehydration salts: one sachet into the volume printed on the packet, normally one litre of bottled or boiled water. Any pharmacy in Vietnam has them and they cost almost nothing.
• If it is mild, drink whatever you will actually finish — water, weak tea, a sports drink. The best rehydration fluid is the one that gets drunk.
• Do not sit there working through cola or fruit juice. Very sweet drinks draw water into the gut and can make the diarrhoea worse. This is the most common mistake.
• Sip small amounts often if you feel sick. Large gulps come straight back up.
• Eat when you feel able to, plainly, and skip fat and spice for a day or two. Prolonged fasting does not speed anything up.

When it is not just a stomach bug

This is the part that makes Vietnam different from being ill at home, and the reason not to simply wait it out.

Dengue is present year-round across much of the country, and early dengue can look like a rough stomach and a fever. Typhoid travels the same food-and-water route as ordinary traveller's diarrhoea — vaccination is recommended for most visitors and is not fully protective, so it stays on the list even if you had the jab. Hepatitis A arrives the same way.

None of that means your bad night is something serious; usually it is not. It means that diarrhoea plus fever in Vietnam is not automatically “something I ate”, and that is worth ten minutes with a doctor rather than three more days of guessing.

What a consultation actually achieves

For most people this is not about obtaining a prescription. It is about someone competent deciding which of the three boxes above you are in, and ruling out the conditions that look similar.

• A proper examination, including how dehydrated you actually are — which is genuinely hard to judge about yourself
• A rapid test on the spot when a fever needs explaining, which is what separates a stomach bug from something treated differently
• Fluids given intravenously if drinking has stopped working — as a treatment, not an upgrade
• An antibiotic only if the picture calls for one, and the right one, rather than whatever a pharmacy counter hands over
• An itemised invoice and a written report in English, which is what your travel insurer will ask for

Being seen where you are already lying down is worth more here than it sounds. A taxi ride across an unfamiliar city, in the state you are in, followed by a waiting room, is how people end up delaying until day five.

The short version

Most cases settle in five to seven days, with the vomiting stopping well before the rest. If you are not clearly improving by day three, or a fever appears, stop waiting and have someone look at you. In Vietnam that is a phone call, not an expedition.