2.3 Bacterial Disease: E. coli, Typhoid and Dysentery

Bacteria: The Classic Contamination Type

Bacteria are single-celled organisms, and they are the contamination type the water industry has fought longest. Most bacteria in water are harmless, and the family that dominates testing is the one you must know for the assessment: Escherichia coli (E. coli). Most E. coli strains live harmlessly in the gut of warm-blooded animals, which makes the organism the perfect faecal indicator organism: it is present in faeces in enormous numbers, it survives in water broadly as long as the dangerous pathogens do, and it is straightforward to detect in the laboratory. The Drinking Water Inspectorate is explicit that the detection of E. coli indicates faecal contamination. The standard is zero E. coli in any 100 ml sample of treated water. In 2025 the DWI recorded just three E. coli detections at treatment works and four at service reservoirs in England, out of more than 3.6 million microbiological tests. Even one detection triggers investigation, because it proves a pathway exists between faeces and the supply.

E. coli O157: STEC and VTEC

Within the E. coli family sit strains that produce Shiga toxin. UKHSA calls them Shiga toxin-producing E. coli (STEC), also known as verocytotoxin-producing E. coli (VTEC); E. coli O157 is the most common STEC strain found in the UK. Three facts make O157 the bacterial pathogen water workers fear most:

• Silent animal reservoirs. The main reservoir is ruminants - cattle above all, along with sheep. Infected animals carry and shed the bacteria in their faeces with no signs of illness whatsoever. A field of perfectly healthy-looking cattle can still be shedding O157 into slurry and run-off.
• A very low infectious dose. UKHSA guidance states that the organism is highly virulent and the infectious dose is low - possibly fewer than 100 organisms. Invisible traces of contamination are enough to cause infection, which is why hygiene margins around treated water are absolute rather than proportionate to how much dirt you can see.
• Severe illness in vulnerable people. STEC infection typically begins as diarrhoea, often bloody, and in a small number of people progresses to haemolytic uraemic syndrome (HUS) - a life-threatening complication causing kidney failure, with the risk highest in children aged five and under.

The routes into water mirror Section 2.1 exactly: slurry spreading and run-off into sources and excavations, animal access to catchments and raw water, contaminated boots and tools, and poor hand hygiene after animal contact before working with treated water.

Typhoid and Paratyphoid Fever: Human-Only Diseases

Typhoid fever and paratyphoid fever are caused by the bacteria Salmonella Typhi and Salmonella Paratyphi. Their defining feature is that humans are the only reservoir: the bacteria live in people, spread in human faeces, and reach new mouths through contaminated water, food and hands. The illness is systemic rather than purely gut-led - a high temperature that climbs over several days, headache, cough, chills, aches and pains, with constipation early on and tummy pain and diarrhoea later. Symptoms usually begin within three weeks of infection and can take up to six. Untreated, typhoid can lead to serious complications including internal bleeding and peritonitis.

Historically, typhoid was a mass killer in British cities, spread by sewage-contaminated water, and it is one of the classic reasons the UK built treated, piped supplies. Today it is rare in the UK, and most people who get it have recently travelled to countries where it remains common, such as India, Pakistan or Bangladesh. Crucially, a small number of people who recover become carriers who go on shedding the bacteria for months or years. This is exactly why the EUSR health screening questionnaire asks whether you have had typhoid or paratyphoid in the preceding 12 months, and why anything declared requires written GP confirmation that you are illness- and symptom-free before EUSR registration.

Dysentery

Dysentery is the name for an infection that gives you diarrhoea with blood in it, and sometimes mucus, along with tummy pain and a high temperature; most cases get better within about seven days. There are two forms: bacillary dysentery, caused by Shigella bacteria, and amoebic dysentery, caused by the parasite Entamoeba histolytica. Both spread by the faecal-oral route through contaminated water, food and hands, and dysentery features directly on the EUSR screening list. Shigella is highly infectious, so person-to-person spread and poor hand hygiene after using the toilet matter as much as the state of the water supply.

Cholera and John Snow: Where Water Epidemiology Began

Cholera, caused by Vibrio cholerae, produces severe acute watery diarrhoea - so much fluid loss that the illness can kill within hours if untreated. It is not found in the UK today; cases arise from travel to regions without clean water. Its place in your course is historical and foundational. In 1854, during a cholera epidemic in Soho, London, the physician John Snow mapped the deaths, noticed they clustered around the Broad Street water pump, and persuaded the parish to remove the pump handle on 8 September 1854. The outbreak faded, and Snow's investigation - conducted decades before bacteria were identified as the cause of cholera - founded modern epidemiology and proved the principle behind every water hygiene card: contaminated drinking water transmits disease, and interrupting the water link stops the outbreak.

Comparison Table

Why the Screening List Maps Exactly Onto This Section

Typhoid, paratyphoid and dysentery - three of the declared illnesses on the EUSR questionnaire - are precisely the diseases above, and persistent diarrhoea or vomiting and prolonged unexplained fever are their calling cards. Declaring illness is not an admission of failure; it is the mechanism that keeps a potentially shedding individual away from treated water until they are medically confirmed clear. Illness reporting plus exclusion protects the public; concealment puts an entire supply at risk.

Common Candidate Traps

• 'E. coli O157 makes cattle visibly ill.' It does not. Carriage is silent, so healthy-looking herds can still contaminate slurry, fields and run-off.
• 'Typhoid is extinct.' It is rare in the UK and usually travel-associated, but imported cases and long-term carriers occur - which is why screening asks about the last 12 months rather than the last century.
• 'Only faeces, not slurry, carry these organisms.' Slurry is animal faeces mixed with urine and bedding - a concentrated bacterial and protozoal load, and a first-class vehicle for the faecal-oral route.