Friendly Bacteria for a Worry-Free Trip

Introduction

Brief overview of traveller’s diarrhoea (TD)

Traveller's diarrhoea (TD) is generally not serious, but it can be highly unpleasant. It causes liquid stools and abdominal cramps. But what puts you at risk of getting it? Basically, food or water that is contaminated, so be careful with what you consume while travelling.

Also, although it usually disappears naturally, sometimes, depending on the place, it is recommended to carry medications approved by your doctor.¹

Common causes 

There are times when it may be due to the impact that a change in diet or even the stress of the trip itself can cause. But generally, bacteria, viruses, or parasites are the main causes. These are sometimes found in faeces from contaminated food or water.

The inhabitants of at-risk countries are not affected because their organisms have learned to deal with these bacteria and have achieved complete immunity.¹

Role of gut microbiota in digestion and immunity

Your gut flora is capable of breaking down carbohydrates and fibres that the body cannot break down on its own. They also produce essential enzymes to create vitamins such as B1 and produce short-chain fatty acids, an essential nutrient.²

Also, at the immunological level, it plays an important role in the stimulation, training, and functioning of the system. Microorganisms, which, as we know, are constantly evolving, have made the human immune system evolve over the years as well to maintain symbiosis.³

Introduction to probiotics as a preventive measure

Probiotics vary greatly in their activity, although there is some evidence supporting their use. As we mentioned, probiotics are capable of maintaining a balanced gut microbiome, which could potentially reduce the risk of developing TD. Even so, there is still no conclusive evidence.⁴

Understanding probiotics

Definition and types of probiotics

Probiotics are microbes that are not harmful to our body, but rather, on the contrary, they are beneficial, since they help to maintain good health. For example, they keep harmful microbes at bay or collaborate with other populations of beneficial microbes that already live in our body. They can be applied topically on the skin, the nose, or the genitals, or also be ingested orally.¹

Common strains used

The most used strains are:⁵

• Lactobacillus: Gram-positive, rod-shaped bacteria characterised by producing lactic acid from glucose metabolism⁶
• Bifidobacterium: Gram-positive anaerobic rod-shaped bacteria that also produce lactic acid.⁷
• Saccharomyces: Yeast capable of converting sugar into carbon dioxide and alcohol through enzymes⁸
• Streptococcus: Non-motile, gram-positive, spherical bacteria that accumulate in a bead-like chain formation⁹
• Enterococcus: Gram-positive spherical bacteria with high survival capacity, capable of colonising soil, food, or water under various climatic conditions¹⁰
• Escherichia: Gram-negative facultative anaerobic rod-shaped bacteria¹¹
• Bacillus: Rod-shaped, gram-positive, aerobic, and sometimes anaerobic bacteria that colonise soil and water¹²
• Mechanisms of action in gut health

Probiotics are capable of competing with pathogenic microbes for nutrients, making their survival in the intestine more difficult. They can also produce antimicrobial agents, such as hydrogen peroxide (oxygenated water), improve the function of the intestinal barrier by stimulating the production of mucin proteins, and regulate the expression of important proteins, as well as modulate the immune response in the intestine.¹³

TD: causes and risk factors

Primary pathogens 

The most common cause is bacteria. The most recognised pathogens are Enterotoxigenic Escherichia coli, followed by Campylobacter jejuni, Shigella spp. and Salmonella spp.. Other types of E. coli are also found, and other species such as Aeromonas spp. and Plesiomonas spp. have been identified. Additionally, new pathogens such as Acrobacter are suspected.

Certain viruses can also cause diarrhoea, including astrovirus, norovirus, and rotavirus.

Protozoa are also associated with pathogens, highlighting Giardia. Other protozoa, such as Cyclospora, depend on geography and seasonality (with higher risk in Guatemala, Haiti, Nepal, and Peru). Entamoeba histolytica and Cryptosporidium are uncommon but should also be taken into account. Lastly, Dientamoeba fragilis has also been associated with TD.¹⁴

Risk factors 

To begin with, it affects both men and women and is more common in young adults. In a single trip, it can occur multiple times and can also vary depending on the seasons. For example, in countries with hot climates, the rates are higher.

Additionally, the lack of access to pipelines or latrines facilitates the spread of disease-transmitting vectors (such as flies). Poor refrigeration, frequent blackouts that make food preservation difficult, lack of potable water, and inadequate hygiene, such as poor handwashing technique, also increase the risk.¹⁴

Symptoms and typical duration

It usually appears during the trip or shortly after and generally goes away within one or two days without treatment, with a full recovery in about a week.

The most common symptoms include vomiting, nausea, fever, stomach cramps, urgent need to go to the bathroom, and more than three watery stools per day.

In some cases, high fever, bloody stools, intense pain in the abdomen or rectum, and moderate to severe dehydration may occur.¹⁵

Probiotics as a preventive strategy

How probiotics help prevent TD

Probiotics, as we explained before, are capable of strengthening the gut microbiome, potentially allowing them to outcompete harmful bacteria and enhance the immune response against them, helping to prevent TD.^16,17

Clinical evidence supporting probiotic use

Studies on probiotics for TD have shown inconsistent and heterogeneous results. Of the three published meta-analyses, two did not find a significant reduction in TD incidence, while one did report a notable decrease.

Recent evidence indicates that the efficacy of probiotics depends on both the strain used and the specific disease. Therefore, experts recommend evaluating their effectiveness within subgroups of the same strain or strain combinations for a specific indication. Additionally, it is suggested that there be at least two randomised controlled trials for each type of probiotic to confirm its efficacy.

In particular, Saccharomyces boulardii has been shown to reduce the risk of TD in some studies, with a significant decrease in the incidence of the disease.^18,19,20

Most effective strains 

The data supporting the use of probiotics in TD are increasingly solid, and many articles defend different types of strains. However, there is still much work to be done. For example, although Lactobacillus rhamnosus GG (LGG)is the most effective probiotic reported to date for acute infectious diarrhoea, the lack of information makes centres such as the Centers for Disease Control and Prevention (CDC) in the U.S. consider that the data are not sufficient to support the use of LGG in the prevention of TD of bacterial origin.

Therefore, it is too early to determine with 100% certainty which strain is the most efficient, as there is still debate and a lack of information.²¹

Timing: When to start taking probiotics before travel

It is recommended to take probiotics at least two weeks before the start of the trip. This facilitates the growth of beneficial bacteria in the gut. Additionally, it is important to continue taking them during the trip and for up to two weeks after returning home.²²

Additional preventive measures

Safe food and water practices

When it comes to food, there are several important considerations to keep in mind:²³

• Dry or packaged foods are generally safe if they have not been opened.
• Avoid eating lukewarm food, as it is the temperature at which bacteria grow most easily. If food is meant to be served cold, eat it cold, and the same applies to hot food.
• Avoid raw foods, especially fruits and vegetables that have been pre-cut. If you can peel and wash them yourself, even better. Also, avoid fresh salads or sauces made with raw fruits and vegetables.
• Limit the consumption of raw meat or seafood.

Street food: Street food is part of the experience in many countries. However, make sure that the food is well-cooked and avoid raw vegetables.

Bushmeat: Bats, monkeys, or rodents can carry many diseases, so it is best to avoid consuming them.

When it comes to drinks, it is important to:²³

• Avoid drinking tap water in countries where it is not potable unless you disinfect it by boiling, filtering, or chemically treating it. Also, avoid swallowing it while showering or brushing your teeth. In these countries, it is also best to avoid ice
• Bottled or canned drinks are the safest option. However, be cautious, as some vendors may refill bottles with untreated water. With carbonated drinks, this is easier to detect because an unopened bottle will have bubbles. Also, avoid ice
• Do not drink hot beverages that are at room temperature, and be careful with added ingredients. Sugar is generally safe
• Avoid drinking milk from open containers such as pitchers, and avoid unpasteurized milk, cheese, or yoghurt, especially if you have a weakened immune system or are pregnant
• Alcoholic beverages generally contain enough alcohol to kill microbes. However, avoid ice and added ingredients such as fruit juices
• Fountain drinks in restaurants are usually made with tap water, so it is best to consider other options
• It is best to consume juices that you prepare yourself

Importance of hand hygiene

It has been proven that handwashing can reduce diarrhoea by 30% in children, regardless of the country and economic status. In the end, most pathogens are transmitted through water contaminated with faecal matter, and in various actions, humans tend to bring their hands to their faces.²⁴

Use of oral rehydration solutions (ORS) in case of TD

Oral rehydration salt (ORS) solution is used to replace fluids and electrolytes lost due to diarrhoea. It is made of water and salts in specific proportions. It can be found in pharmacies, usually in powder form, although it is also possible to prepare it at home (link).²⁵

Limitations and considerations

Possible side effects and contraindications

The few available studies have shown positive results and seem to confirm that probiotics are safe for healthy individuals. However, there are small risks for immunocompromised individuals, those with critical illnesses, and premature babies.

In some cases, probiotics may contain, in addition to beneficial microorganisms, a harmful microbe that has accidentally slipped in. Although this is very unlikely, it could pose a problem for individuals with a weakened immune system.¹

Regulatory status and quality control of probiotic supplements

Tests must be conducted to prove that the probiotic is safe and effective before it is marketed. Generally, they are considered dietary supplements and are regulated by the FDA’s Centre for Food Safety and Applied Nutrition.²⁶

As a dietary supplement, by law, they must contain at least one of the following elements:

• An amino acid
• A metabolite
• A constituent
• An extract
• A dietary substance used to increase total dietary intake
• An herb or other botanical (excluding tobacco)
• A mineral
• A vitamin
• A concentrate
• Or a combination of any of the above.

Summary

TD is quite common in certain countries and is mainly caused by pathogens found in contaminated water. Although it usually resolves on its own, it can be prevented with hygiene precautions and possibly probiotics.

These probiotics are beneficial microorganisms that help balance gut flora, strengthen immunity, and compete with harmful microbes. Some strains, such as Saccharomyces boulardii, have shown potential in reducing the risk of TD, although the evidence remains inconclusive. Their effectiveness varies depending on the strain used, and their use should be evaluated in specific cases with controlled studies.