17.6 — Gut Infections

Diarrhoeal disease killed an estimated 4.6 million children a year in 1980. Today it is around 440,000 — a reduction of over 90 percent.

The intervention responsible was not a drug or a vaccine. It was oral rehydration solution: water, salt and sugar, in the right ratio, exploiting a carrier protein in the gut lining (Chapter 1.4).

It costs a few pence, needs no needle, no refrigeration and no clinician, and The Lancet called it potentially the most important medical advance of the twentieth century.

What causes it

Viral — the majority.

Norovirus — the winter vomiting bug. Extremely infectious: as few as 18 viral particles can cause infection, and it survives on surfaces and resists alcohol gel (Chapter 17.4). Which is why outbreaks sweep through cruise ships, schools and hospitals so efficiently, and why soap and water rather than gel is the advice.

Sudden vomiting and diarrhoea for 24 to 48 hours, and immunity is short-lived, so you can catch it again the same season.

Rotavirus — the leading cause of severe childhood diarrhoea before vaccination.

And the rotavirus vaccine has had a large effect: hospital admissions for gastroenteritis in young children have fallen by 50 to 80 percent in countries that introduced it.

Bacterial — less common, generally more severe.

Campylobacter — the commonest bacterial cause in many high-income countries, usually from undercooked chicken. Bloody diarrhoea and severe cramping. It is the commonest identified trigger for Guillain–Barré syndrome (Chapter 11.8), through molecular mimicry.

Salmonella — poultry, eggs, reptiles.

Shigella — very low infectious dose, spreads person to person, bloody diarrhoea.

E. coli — several types.

And one deserves specific attention. Shiga toxin-producing E. coli, including O157, causes bloody diarrhoea and can lead to haemolytic uraemic syndrome — red cell destruction, low platelets and kidney failure, mostly in young children.

And here is a critical practical point: antibiotics increase the risk of haemolytic uraemic syndrome in this infection, apparently by increasing toxin release. Which is one reason bloody diarrhoea is not treated with antibiotics on spec.

Clostridioides difficile — Chapter 9.6.

Vibrio cholerae — Chapter 1.4.

Parasitic — Giardia, Entamoeba, Cryptosporidium (Chapter 17.3).

And a distinguishing feature: parasitic infection tends to cause prolonged diarrhoea lasting weeks rather than days, which is what should prompt testing.

Food poisoning from preformed toxin — Staphylococcus aureus and Bacillus cereus.

And the timing identifies it. Vomiting within 1 to 6 hours of eating means preformed toxin, not infection — the organism did not have to grow in you. Classically from rice left at room temperature, and from cream or mayonnaise-based foods.

What actually matters

Not the organism. The hydration.

In almost all gut infection, the person recovers regardless of the cause, and what determines the outcome is whether they stay hydrated.

Assessing dehydration (Chapter 10.3): thirst, dry mouth, reduced urine, sunken eyes, poor skin turgor, and — later — fast pulse and low blood pressure. In children, a sunken fontanelle, absent tears, and lethargy.

Weight change is the most accurate measure, and in a child a recent weight is genuinely useful.

Oral rehydration solution — the WHO reduced-osmolarity formula is 75 mmol/L sodium, 75 mmol/L glucose, plus potassium and citrate, totalling about 245 mOsm/L (Chapter 1.4).

And the ratio matters. Too much sugar makes the solution hypertonic and pulls water into the bowel, worsening the diarrhoea — which is why ordinary fizzy drinks and undiluted fruit juice are poor choices.

Sachets are cheap and available everywhere, and they are preferable to a home-made version.

The home recipe, for when nothing else is available: six level teaspoons of sugar and half a level teaspoon of salt in one litre of clean water. Getting the salt wrong is the dangerous error, in either direction — too much causes hypernatraemia, too little does not work.

Give small amounts frequently, particularly if vomiting — a few sips every few minutes rather than a glass at once.

And continue feeding. The old advice to rest the gut was wrong. Continued feeding shortens the illness and improves nutrition, and breastfeeding should continue throughout.

Treatment beyond fluids

Antibiotics are usually not needed, and frequently harmful — they prolong Salmonella carriage, increase haemolytic uraemic syndrome risk in E. coli O157, and cause C. difficile.

When they are used: severe illness with systemic features, immunosuppression, suspected cholera or typhoid, some travellers' diarrhoea, and identified parasitic infection.

Antimotility drugs (loperamide) — useful for convenience in mild illness in adults. Avoided where there is fever or blood, because slowing the gut retains the pathogen and its toxins. Not used in young children.

Anti-sickness drugs — ondansetron in children reduces vomiting and improves the success of oral rehydration, which is a genuinely useful and relatively recent addition.

Zinc supplementation for 10 to 14 days reduces the duration and severity of diarrhoea in children in low-income settings, and it is a WHO recommendation alongside oral rehydration.

Probiotics — specific strains have modest evidence for shortening infectious diarrhoea and for preventing antibiotic-associated diarrhoea. The category as a whole is a marketing term (Chapter 9.6).

Typhoid

Different from ordinary gastroenteritis, and worth separating.

Salmonella Typhi, spread by contaminated food and water.

Presents with progressive fever over days, headache, abdominal pain and — characteristically — constipation more often than diarrhoea in the first week.

Untreated it can cause intestinal perforation and bleeding, and mortality was historically 10 to 20 percent.

It responds to antibiotics, and resistance is a growing problem — extensively drug-resistant strains have emerged in South Asia.

Vaccines are available and are recommended for travel to endemic areas, alongside food and water precautions.

Travellers' diarrhoea

Affects 20 to 50 percent of travellers to high-risk regions.

Prevention, in order of usefulness: bottled or boiled water — including for teeth, and no ice; hot, freshly cooked food; fruit you peel yourself; and avoiding salads and unpasteurised dairy.

"Boil it, cook it, peel it, or forget it" remains the practical rule.

Treatment is fluids. A standby antibiotic is sometimes carried for severe illness during travel, and its routine use is discouraged given resistance.

And a note on what actually transmits it: hand hygiene matters more than food choice in many outbreaks.

When to seek help

Blood in the stool.High fever.Signs of dehydration — reduced urine, dizziness on standing, lethargy. Severe abdominal pain.Symptoms beyond a week, or beyond a few days in a child. Recent hospital admission or antibiotics — think C. difficile. Recent travel to a high-risk area.And a lower threshold in infants, older people, pregnancy and immunosuppression.

In an infant: fewer wet nappies, no tears, drowsiness or a sunken fontanelle are the signs that matter.

Preventing it

Handwashing with soap — the single most effective measure, and alcohol gel does not work against norovirus.

Food handling — separate raw and cooked, cook thoroughly, chill promptly, and do not leave cooked rice at room temperature.

Water safety when travelling.

Vaccination — rotavirus in infancy, typhoid and cholera for travel.

And staying away from others while infectious. The usual advice is 48 hours after symptoms stop, which matters most for people who handle food or work in healthcare.

What has changed

The scale of improvement here is worth restating.

Child deaths from diarrhoea down by over 90 percent since 1980.

Rotavirus vaccination has removed the commonest cause of severe childhood gastroenteritis in the countries that use it.

Clean water and sanitation continue to do more than any medical intervention — and around 2 billion people still lack safely managed drinking water, which is where the remaining deaths are.

These are solvable problems with known solutions, which is a different situation from a disease nobody knows how to treat.

What the next page fixes

Chapter 17.7 covers the infections carried by insects — malaria above all, which has shaped the human genome more than any other pathogen and which is, slowly, being pushed back.