Food and Waterborne Disease

TL;DR. These diseases all work the same way: something that came out of a person or animal ends up in something you swallow. The faecal-oral route is the crudest transmission mechanism in medicine and the most consequential, because it kills through dehydration rather than through any clever biology. Cholera can drain 20 litres of fluid from an adult in a day, and until 1970 the treatment required intravenous drips and a hospital. Then someone worked out that adding glucose to salt water makes the gut absorb both, and the treatment became a sachet of powder that a parent can mix at home. Oral rehydration therapy has saved tens of millions of lives, and it is the single best example in this book of a cheap idea beating an expensive one.

Key takeaways

• Diarrhoeal disease still kills hundreds of thousands of children under 5 every year, almost entirely from dehydration, and almost all of it is preventable and treatable.
• Oral rehydration solution works because glucose and sodium are absorbed together by a co-transporter in the gut wall that keeps working even when the gut is inflamed. The Lancet called it potentially the most important medical advance of the twentieth century.
• John Snow's 1854 investigation of the Broad Street pump founded epidemiology and demonstrated that cholera was waterborne, decades before anyone accepted germ theory.
• Sanitation and clean water did more for human health than any drug. The largest falls in infectious mortality in industrialised countries happened before antibiotics existed.
• Antibiotics are usually the wrong treatment for infectious diarrhoea, and in some cases (E. coli O157) they make the outcome considerably worse.
• Typhoid, cholera, hepatitis A, and rotavirus all have vaccines, and their use is expanding.

What they are

In short: A dozen organisms sharing one route, from faeces to mouth, and differing mainly in whether they invade, poison, or simply overwhelm.

The history

In short: John Snow's 1854 map founded epidemiology, and sewers ended cholera in Western cities decades before any antibiotic existed.

Cholera arrived in Europe from the Ganges delta in a series of pandemics from 1817 onward, and its speed terrified cities: a healthy adult could die within twelve hours.

London, 1854. The prevailing theory was miasma, that disease came from bad air. John Snow, a physician who had argued for waterborne transmission, mapped deaths in Soho and found them clustered around the public water pump on Broad Street. He identified anomalies that strengthened rather than weakened the case: the workers at the local brewery, who drank beer, were unaffected; a woman in Hampstead who died had the Broad Street water delivered because she liked the taste. He persuaded the parish to remove the pump handle. The outbreak was already declining, so the handle removal was less decisive than legend has it, but the method (map the cases, find the common exposure, remove it) created modern epidemiology.

Snow's larger study compared households supplied by two water companies, one drawing from the Thames upstream of London's sewage and one downstream, and found death rates differing by roughly a factor of nine. It is one of the finest natural experiments ever conducted.

The sanitary revolution followed: London's sewer system built by Joseph Bazalgette after the Great Stink of 1858, water filtration, then chlorination from 1908. Typhoid and cholera disappeared from Western cities before any antibiotic existed. The mortality decline in industrialising countries between 1850 and 1940 owes more to sewers, water treatment, and food regulation than to medicine.

1968 to 1971: oral rehydration. Researchers in Dhaka and Calcutta showed that a solution of glucose and salt taken by mouth could replace intravenous fluid for cholera. Its first mass use came during the 1971 Bangladesh war of independence, in refugee camps where intravenous fluids were unavailable: mortality among treated cholera patients fell from around 30 percent to roughly 3 percent. UNICEF and WHO adopted it globally in the 1970s and 1980s.

What actually goes wrong

In short: Cholera toxin locks a cellular switch on so the gut pumps out water, and the transporter that oral rehydration exploits keeps working throughout.

Cholera is the purest illustration. V. cholerae is not invasive: it colonises the small intestine and secretes cholera toxin, which locks a cellular signalling switch permanently on. The result is that intestinal cells pump chloride out into the gut lumen continuously, and water follows by osmosis. The patient loses litres per hour of a clear fluid with flecks of mucus, the classic "rice water" stool. Death is from hypovolaemic shock and electrolyte loss, and it can come within hours. The gut lining is not destroyed, which is why oral rehydration works.

Why oral rehydration works. The intestinal wall has a sodium-glucose co-transporter (SGLT1) that moves one glucose molecule and one sodium ion together into the cell. Water follows. That transporter keeps functioning during cholera. Salt water alone is absorbed poorly; glucose plus salt is absorbed efficiently. This is not folk wisdom; it is a specific piece of membrane physiology, and understanding it turned a hospital disease into a home one. The same transporter, blocked rather than exploited, is the target of the SGLT2 inhibitors in Chapter 18, which is a pleasing symmetry.

Invasive versus toxin-mediated. Shigella and invasive E. coli penetrate the intestinal wall, producing bloody diarrhoea, fever, and systemic illness. Salmonella Typhi goes further: it is taken up by immune cells and disseminates through the bloodstream, producing a systemic fever rather than a bowel illness, and it can persist in the gallbladder afterwards, creating chronic carriers who shed bacteria for years while remaining well. Mary Mallon, "Typhoid Mary," a New York cook in the early 1900s, infected dozens of people and was eventually confined for life, an early and unresolved collision between public health and individual liberty.

Toxin at a distance. Shiga toxin from E. coli O157 enters the bloodstream and damages the lining of small vessels, especially in the kidney, causing haemolytic uraemic syndrome: destroyed red cells, low platelets, and acute kidney failure, mainly in children. Antibiotics increase toxin release and are contraindicated, which is a rare and important instance where treating the infection worsens the disease.

Infectious dose varies enormously and explains transmission patterns. Shigella and norovirus need as few as 10 to 100 organisms, so they spread person to person and through whole cruise ships, schools, and hospitals. V. cholerae needs many millions, so it needs contaminated water rather than a handshake.

What it does to the body

In short: Dehydration is the common pathway and the thing that kills, and repeated childhood episodes cause lasting stunting.

Dehydration is the common pathway and the thing to recognise. In a child: sunken eyes, dry mouth, no tears, reduced skin turgor, lethargy, and reduced urine output. In severe cases: rapid weak pulse, cold extremities, and shock. Death from diarrhoeal disease is almost always death from fluid loss, not from the organism.

Longer-term consequences are underappreciated:

• Malnutrition. Repeated diarrhoeal episodes in early childhood impair nutrient absorption and drive stunting, with lifelong effects on growth and cognition. Diarrhoea and malnutrition reinforce each other: each makes the other more likely and more severe.
• Environmental enteric dysfunction: chronic exposure to faecal contamination changes the gut lining structurally, reducing absorption even between infections. This is a leading hypothesis for why nutrition programmes alone often fail to reverse stunting without sanitation.
• Post-infectious irritable bowel syndrome after a bout of bacterial gastroenteritis.
• Guillain-Barré syndrome, an ascending paralysis from an immune attack on nerves, in a small number of Campylobacter infections.
• Reactive arthritis after several bacterial enteric infections.

Is it deadly?

Yes, and overwhelmingly to children in poor countries.

• Diarrhoeal disease remains among the leading causes of death in children under 5, causing hundreds of thousands of deaths a year, essentially all from dehydration and preventable with a few cents of oral rehydration salts and zinc.
• Cholera kills a substantial fraction of severe untreated cases within hours; treated promptly, mortality is under 1 percent. Outbreaks track war, displacement, and infrastructure collapse: Haiti after 2010, Yemen after 2016 (the largest recorded outbreak, over a million suspected cases), and recurrent outbreaks in conflict zones.
• Typhoid causes an estimated 9 million illnesses and over 100,000 deaths a year, with drug-resistant strains spreading, including extensively drug-resistant typhoid in Pakistan since 2016.
• Rotavirus killed hundreds of thousands of infants a year before vaccination and remains a major cause where the vaccine has not been introduced.

Is it contagious?

Yes, and by an unglamorous route. All of these travel from faeces to mouth, whether through water, food, hands, surfaces, or flies.

Two special notes. Norovirus additionally aerosolises during vomiting, survives on surfaces, resists many disinfectants including alcohol gels (soap and water, and bleach, are needed), and requires a tiny dose, which is why it closes hospital wards, cruise ships, and schools. Asymptomatic carriage is common for typhoid, polio, and several others, so "nobody here is sick" does not mean nobody here is shedding.

Who gets it

In short: Two billion people without safely managed drinking water, and in rich countries the burden shifts to industrial food safety failures.

Where sanitation is lacking. Roughly 2 billion people still lack safely managed drinking water and a larger number lack safely managed sanitation. Hundreds of millions still practise open defecation. That is the entire explanation for the geographic distribution of these diseases.

Children under 5, because of immature immunity, smaller fluid reserves relative to losses, and hand-to-mouth behaviour.

Travellers: traveller's diarrhoea affects a large fraction of visitors to low-sanitation regions, usually from enterotoxigenic E. coli.

In high-income countries, the burden shifts to food safety failures in industrial production: Campylobacter in poultry, Salmonella in eggs and produce, Listeria in chilled ready-to-eat foods, and E. coli O157 in beef and leafy greens. Outbreaks are larger and more geographically dispersed than they used to be, precisely because food supply chains are centralised: one contaminated production lot can reach a dozen countries.

Higher risk of severe disease: infants, older adults, pregnant women (Listeria and hepatitis E especially), people with reduced stomach acid (including those on proton pump inhibitors, since acid is a major defence), and the immunosuppressed.

Treatment, and how it works

In short: Rehydration first and always, zinc in children, and usually no antibiotics, which in one case make the outcome considerably worse.

Rehydration first, always.

• Oral rehydration solution (ORS): the WHO reduced-osmolarity formula contains sodium chloride, glucose, potassium chloride, and trisodium citrate in specific proportions. It does not stop the diarrhoea; it replaces what is lost, which is what keeps people alive. A homemade approximation (six level teaspoons of sugar and half a level teaspoon of salt in a litre of clean water) is far better than nothing in an emergency, and the proportions matter, since too much sugar worsens the diarrhoea osmotically.
• Intravenous fluids (Ringer's lactate) for severe dehydration or persistent vomiting.
• Zinc supplementation for 10 to 14 days in children reduces the duration and severity of diarrhoea and the likelihood of recurrence over the following months. It is cheap and still underused.
• Continue feeding. Withholding food, once standard advice, prolongs recovery and worsens nutritional status. Breastfeeding should continue throughout.

Antibiotics: usually not. Most infectious diarrhoea is viral or self-limiting, and antibiotics add side effects, resistance, and, in the case of STEC, real danger. They are indicated for cholera (a single dose shortens illness and reduces shedding), typhoid, shigellosis, severe Campylobacter, and specific parasitic infections.

Antimotility drugs such as loperamide relieve symptoms in mild adult traveller's diarrhoea and should not be used in bloody diarrhoea, fever, or in young children, because slowing the gut retains invasive organisms and toxins.

Vaccines: oral cholera vaccines (used in outbreak and endemic settings, with global supply repeatedly outstripped by demand), typhoid conjugate vaccine (a substantial improvement, effective in young children and now being rolled out in high-burden countries), rotavirus vaccine (in most national schedules), and hepatitis A vaccine.

What treatment costs

• ORS: essentially none. It tastes salty, which is the main barrier to children drinking enough, and flavoured formulations exist.
• Antibiotics: resistance is a growing problem across these organisms, with extensively drug-resistant typhoid the clearest warning. C. difficile colitis, itself a diarrhoeal disease, is a common consequence of antibiotic use for something else.
• Loperamide: dangerous in the wrong context, as above.
• Cholera vaccine: short-lived protection (roughly 2 to 3 years) and limited supply, so it supplements rather than replaces water and sanitation.

What the person can do

In short: Handwashing with soap cuts diarrhoeal disease by roughly a third, and it remains one of the highest-value and least glamorous health behaviours known.

At home and abroad:

• Handwashing with soap at the right moments (after using the toilet, after changing a nappy, before preparing food and eating) reduces diarrhoeal disease by roughly 30 percent in trials. It remains among the highest-value health behaviours known and among the least glamorous.
• Water treatment where supply is unsafe: boiling, chlorination, filtration, or solar disinfection.
• Food safety basics: separate raw and cooked, cook thoroughly (particularly poultry and minced beef), refrigerate promptly, wash produce, and avoid unpasteurised milk. In pregnancy, avoid soft cheeses, pâté, and chilled ready-to-eat meats because of Listeria.
• Travellers: the old rule ("boil it, cook it, peel it, or forget it") is still the shape of the advice, with ice and salads being the classic traps. Take ORS sachets. Antibiotics for self-treatment are prescribed less often than they used to be, given resistance concerns.
• Know when to seek care: blood in the stool, high fever, signs of dehydration, diarrhoea lasting more than a few days, or any diarrhoea in a young infant or a frail older person.

At the population level, the interventions that matter are not medical: piped water, sewerage, treatment plants, food regulation, and inspection. This is the argument for considering infrastructure a health intervention, and it is why sanitation engineers have saved more lives than most physicians.

Living with it

For the world's poorest children, these are not discrete events but a recurring background that suppresses growth and school performance. The consequence of repeated early-life diarrhoea is measurable decades later in adult height, cognitive test scores, and earnings, which reframes sanitation from a comfort issue to an economic one.

What's next

• Typhoid conjugate vaccine rollout, which has shown high efficacy in trials in Nepal, Malawi, and Bangladesh and is the main tool against drug-resistant typhoid.
• Better cholera vaccine supply, currently the binding constraint during outbreaks.
• Next-generation ORS formulations aiming to reduce stool output as well as replace fluid.
• Sanitation at scale, which remains the fundamental answer and a large unfinished infrastructure project.
• Genomic outbreak tracing, now routine in food safety agencies, which detects multi-country outbreaks from a handful of cases that would previously have looked unrelated.

Sources and notes

Oral rehydration history and the 1971 Bangladesh refugee camp experience: Mahalanabis et al., and subsequent reviews; The Lancet's 1978 editorial described ORT as "potentially the most important medical advance this century." SGLT1 co-transport basis of ORS: Curran and colleagues' physiology work in the 1960s. John Snow: On the Mode of Communication of Cholera, 2nd edition, 1855. Diarrhoeal mortality in children: WHO and Global Burden of Disease estimates. Typhoid burden: GBD typhoid and paratyphoid collaborators. Yemen cholera outbreak scale: WHO surveillance. Handwashing effect size: Cochrane reviews of hand hygiene for diarrhoea prevention. Zinc in childhood diarrhoea: WHO/UNICEF joint statement and supporting trials. Antibiotics and haemolytic uraemic syndrome risk in STEC: Wong et al., NEJM, 2000, and subsequent analyses.

Open questions. Whether antibiotics genuinely increase HUS risk in all STEC contexts is still debated, though the caution stands. Why sanitation interventions in trials have sometimes failed to reduce stunting as much as expected is an active and important puzzle.

Next: the infections that travel through the most avoided conversation in medicine. 👉