Breaking all rules within 1 hour of landing - does "boil it, cook it, peel it, or forget it" really prevent traveller's diarrhoea?

As a travel doctor, I'm always teaching patients the golden rules to avoid traveller's diarrhoea and the old adage "boil it, cook it, peel it, or forget it". Unfortunately these rules can be difficult to follow, especially when you're in a new place keen to try the local cuisine. In fact, studies have shown that 95-99% of all travellers (Shlim 2005; Cabada 2006) make at least one dietary mistake during their trips.

I, being an adventurous eater, am no exception to the statistics. In my case it was within an hour of landing in Ho Chi Minh City, Vietnam. My friend and I were hungry and after dropping off our luggage we made our way on foot to Ben Thanh Market, Ho Chi Minh City's largest market.

Ben Thanh Market

To get there we had to cross 6 lanes of traffic with no traffic lights or pedestrian crossings in sight. It was a hairy task on our first day there, but luckily by the end of the trip we had mastered the art of crossing the road in South East Asia.

Ben Thanh market was indeed huge. There were produce stores and dry goods stores, and shop owners were constantly touching us to try and get our attention. Once in the food section though, things got even worse, perhaps because we were pausing to consider our options. As if we were water in a drought, shop owners flocked out of nowhere trying to shove their picture menus under our noses.

Food stalls inside the market

It was very overwhelming and we walked quickly away to avoid the crowd, not making any eye contact with anyone. It was then we spotted a store, with many locals sitting around it. They paid us no attention and for a few minutes we just watched the happenings in peace. As soon as a seat was emptied it would be filled by someone new, and the shop was doing a lot of takeaway business as well. If the locals love it, surely it will be something good right?

And indeed it was. I ordered what everyone was having, a banh beo hue for 13000 dong and a sugar cane drink for 5000 dong - such a bargain at less than $1 AUD for lunch! Actually to this day I still don't know what a banh beo hue is! It was very delicious though, and I could probably have eaten another serving.

My banh beo hue, I still don't know what it actually is...

The drink I ordered arrived and it was only then that I realised it had ice in it - my own travel doctor voice ringing in my head, "ice may be made from tap water or be easily contaminated so is best avoided". The weather was hot; I was thirsty; the shop attendant was busy; plus I didn't want to bother to explain about the ice; so I drank it anyway. It was easy to do and I'm sure many have had similar experiences.

And come to think of it, the banh beo hue was probably not very safe either. It was served at room temperature, the items and the sauces were probably made earlier and were not refrigerated in the hot weather. The solace though was the number of locals eating at the stall which showed that the locals trust this place and also hopefully ensured a quick turnover of ingredients. Still, I was dreading falling ill on my first day of the trip.

Luckily I was fine. And after many years of travel in Asia, Africa and South America, thankfully the only time that I had been struck down with high fevers and severe diarrhoea was in Singapore, ironically one of the most hygienic places in the world. Maybe it was Murphy's Law, but then I wondered, do these advice about safe eating really help prevent traveller's diarrhoea? Let's firstly explore what causes traveller's diarrhoea and recap these rules.

Icy drinks, refreshing, but maybe not so safe

What is traveller's diarrhoea?

Bali belly, Delhi belly, Montezuma's revenge, Tourista, or just plainly "stomach bug" or "gastro", traveller's diarrhoea is the most common illness experienced by travellers in tropical or developing countries. There are many "bugs" or "germs" that can cause this, including bacteria such as E Coli, Campylobacter, Salmonella, Shigella; viruses such as Norovirus and Rotavirus; and parasites such as Giardia. What is more commonly known as "food poisoning" is caused by ingestion of toxins made by some bacteria. Some of these toxins can be heat stable which means that they can withstand the heat of cooking.

Symptoms include vomiting, diarrhoea (which can be bloody), abdominal cramps and fevers. It can be just plainly annoying or quite a misery; time is lost from sightseeing and activities; or in serious cases it can lead to dehydration and require hospitalisation. Some people can also develop lactose intolerance or irritable bowel syndrome after a bout of gastro. So it makes sense that we try our best to prevent getting it in the first place.

How to prevent traveller's diarrhoea? Boil it, cook it, peel it, or forget it!

  • Wash your hands prior to eating, or if not possible use alcoholic hand sanitiser.
  • Boil it - Avoid tap water. Drink only boiled, purified or bottled water (but beware that the seal had not been tampered with). Brush your teeth in safe water.
  • Cook it - Eat only things that are freshly cooked and served piping hot. Avoid undercooked or raw meat and seafood (even if cured in citrus juice eg ceviche). Beware of food that had been cooked earlier and are only reheated before serving; beware of buffets.
  • Peel it - Only eat fruits that can be peeled and you should peel the skin yourself after washing your hands.
  • Avoid ice which may be made with tap water. Some may say the ice with a hole in it is safe but it can still be easily be contaminated during storage. The freezing process will only kill 90% of bacteria. Alcoholic drinks will not kill the rest of the bacteria (unless your alcohol is over 70%!).
  • Avoid salads and raw vegetables which may be easily contaminated
  • Drink only pasteurised milk or dairy products.
  • Beware of flies which may perhaps have visited a pile of poo before landing on your food

Do these rules actually work?

Unfortunately, there is limited evidence that following these rules actually reduce the risk of acquiring traveller's diarrhoea. Shlim (2005) reviewed a number of articles which found that the risk of getting traveller's diarrhoea is 30-50% regardless whether these rules have been followed. Cabada (2006) did show that an increased number of dietary mistakes may increase the risk of a traveller falling sick, but making no mistakes certainly did not protect the travellers in the study.

That is depressing news - basically you're damned if you do, and damned if you don't.

Both Shlim and Cabada suggested that the reason behind this is that travellers often eat out at restaurants where the handling and preparation of food may be poor. Apart from the lack of hand washing and poor food handling by kitchen staff, refrigeration may be lacking; cutting boards, dishes and utensils may not have been sanitised properly; flies and insects may be abundant in the kitchen. 

Unfortunately you're only as safe as the last person, or fly, that handled your food.

Fried tarantula anyone?

What else can we do to prevent traveller's diarrhoea?

Vaccinations - Travellers to developing countries will often be advised to have hepatitis A and typhoid vaccinations to protect from these food/water borne diseases. One dose of hepatitis A vaccine is 95% effective, and a booster 6-12 months later increases this to 100%. Typhoid vaccine however only gives about 80% protection against typhoid.

There had previously been suggested that cholera vaccine (dukoral) may protect from enterotoxic E Coli (ETEC), a common cause of traveller's diarrhoea, but a 2013 Cochrane review by Ahmed found no benefit.

Probiotics - benefit is only modest and inconsistent, and the efficacy depends on the strain of probiotic, the dose and the location travelled. Lactobacillus rhamnosus GG (NOT the more common Lactobacillus acidophilus) and Saccharomyces boulardii are two strains that show the most promise currently but there is not enough data to make a recommendation at the moment. 

Travelan - Travelan is a product marketed to prevent traveller's diarrhoea. It is produced by injecting cows with strains of enterotoxigenic E Coli (ETEC) then harvesting their colostrum milk which contains high concentrations of antibodies. It needs to be taken with each meal and will only prevent infections from ETEC. The idea sounds promising but unfortunately ETEC is not the only thing that will make you sick and there is no real world evidence to show that this product works.

Bismuth subsalicylate (or Pepto-Bismol), available in USA, can reduce traveller's diarrhoea from 40% to 14% but can only be used for 3 weeks maximum. Side effects may include gastrointestinal upset and blackening of stools and tongue.

And in extreme cases where you have an important event that you simply cannot miss, prophylactic antibiotics may be used, but I hardly ever suggest it as it can promote antibiotic resistance and increase colonisation of superbugs eg ESBL-PE (extended spectrum beta lactamase producing enterobacteriaceac) as shown in a recent study (Kantele 2015).

Eating street food in Bangkok

So what now? What does it all mean?

All of the above sound very depressing but I assure you that I'm not trying to discourage you from travelling overseas or experiencing local food. I will still try my best to abide by the rule of "boil it, cook it, peel it, or forget it", but I also suggest using common sense to assess the risk in individual situations. Basically we want to ensure raw food is stored correctly (so bugs don't grow and release toxins in the food), cooked at a high enough temperature (to kill the bugs), and not contaminated before you eat it (eg handled with clean hands and utensils and separated from uncooked food or insects).

Some may say street foods are not safe but I disagree to a certain extent. With street food it may be easier to see whether these rules are being followed by the vendor. If you can see the vendor using new gloves or clean utensils while preparing the food; if you can see that uncooked food and cooked food are stored and handled separately; if you can see that all the food is cooked thoroughly and served piping hot in clean and disposable containers; if you can ensure that flies haven't landed on your meal, then I don't see a problem. Although more often than not, vendors often do not wash hands or change gloves between preparing food and collecting money, there is no proper refrigeration of food on the street, and the utensils are washed in a bucket of water behind the cart - that's just traveller's diarrhoea waiting to happen. 

Unfortunately with restaurants it is the luck of the draw as we cannot see what is happening behind the closed kitchen doors. Knowing that there is little that we can control when eating at restaurants, it is even more important to learn how to self manage traveller's diarrhoea, and to carry medications for this. I will explore self treatment in another post.


  1. Shlim (2005) Looking for evidence that personal hygiene precautions prevent traveler's diarrhea. Clin Infect Dis 41 Suppl 8: S531-5
  2. Cabada et al (2006) Risk factors associated with diarrhea among international visitors to Cuzco, Peru. Am J Trop Med Hyg 75 (5): 968-972
  3. Ahmed et al (2013) Vaccines for preventing enterotoxigenic Escherichia coli (ETEC) diarrhea. Cochrane Database Syst Rev 7: CD009029 doi 10.1002/14651858 CD009029 pub2
  4. Dupont et al (2009) Expert review of the evidence base for prevention of traveler's diarrhea. J Travel Med 16 (3): 149-60 
  5. McFarland (2007) Meta-analysis of probiotics for the prevention of traveler's diarrhea. Travel Med Infect Dis 5: 97-105
  6. Leder (2015) Advising travellers about management of travellers' diarrhoea. Aus Fam Phyisician 44 (1): 34-37
  7. Kantele et al (2015) Antimicrobials increase travelers' risk of colonization by extended-spectrum betalactamase-producing Enterobacteriaceac. Clin Infect Dis 60 (6): 837-46 

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