Gastrointestinal outbreaks explained: What they are, what causes them, and what the Bronkhorstspruit and Rhodes cases show

Reports of stomach illness in Bronkhorstspruit, in Tshwane, and at Rhodes University in Makhanda have left many South Africans asking what exactly a gastrointestinal outbreak is, how people catch it, and what they should do if they or their children fall ill. This explainer answers those questions using guidance from the World Health Organization (WHO) and the US Centers for Disease Control and Prevention (CDC), alongside what South African authorities have said about the two cases.

What Is a Gastrointestinal Outbreak?

Gastroenteritis is an infection of the stomach and intestines. Its main sign is diarrhoea, which the WHO defines as three or more loose or liquid stools in a day, or more than is normal for the person. Vomiting, nausea, stomach cramps and fever commonly accompany it.

An outbreak is identified when more people than expected fall ill in the same place and over the same period. Health authorities look for what those people have in common, which is usually a shared source such as drinking water, food, or contact with someone who is already sick. In South Africa, the National Institute for Communicable Diseases (NICD) assesses whether a cluster of cases should be formally declared an outbreak. In Bronkhorstspruit, where 408 people were treated between 7 and 18 October, the institute said it was still collecting specimens to make that decision.

What Causes It

According to the WHO, gastrointestinal illness is usually caused by bacteria, viruses or parasites. Among viruses, norovirus, rotavirus, adenovirus and astrovirus are common causes. Among bacteria, the WHO lists E. coli, Salmonella, Shigella and Campylobacter.

In Bronkhorstspruit, NICD tests found norovirus, Campylobacter and Shigella in three of four stool samples examined, along with other pathogens. The Department of Water and Sanitation separately found very high E. coli levels in the treatment works’ water. No cholera was detected. At Rhodes University, the cause has not been established.

How It Spreads

The germs behind these illnesses typically travel from the faeces of an infected person or animal to the mouth of another. The WHO says this happens through contaminated drinking water or food, or directly between people when hygiene is poor. Faecal contamination of water is, in the WHO’s words, the greatest risk to drinking-water safety. The organisation estimates that at least 1.7 billion people worldwide were using a drinking-water source contaminated with faeces in 2022, and that contaminated water causes about 505,000 diarrhoeal deaths a year.

Norovirus, one of the pathogens found in Bronkhorstspruit, is notable for how easily it moves. The CDC says it spreads very quickly and can pass through direct contact with an infected person, through contaminated food or drink, and through touching contaminated surfaces and then putting unwashed fingers in the mouth. That is why it can run through households, schools and student residences in a matter of days.

Chlorine is widely used in water treatment because it kills most of these organisms before the water reaches taps. Authorities say unchlorinated water was distributed from the Bronkhorstspruit Water Treatment Works between 24 September and 14 October, and that the treatment works draws from a river Water and Sanitation Minister Pemmy Majodina described as badly contaminated with sewage pollution.

Symptoms and How Long They Last

For norovirus, the CDC says symptoms usually appear 12 to 48 hours after exposure and most people recover within one to three days. The typical signs are diarrhoea, vomiting, nausea and stomach pain, sometimes with fever, headache and body aches. Other causes can behave differently. Illness from some bacteria, for instance, may involve bloody diarrhoea, which the WHO calls dysentery, and it can last longer.

People can remain contagious after they begin to feel better. The CDC advises staying home until at least 48 hours after symptoms have stopped and washing hands thoroughly with soap and water for at least 20 seconds, particularly after using the toilet and before preparing food.

The Real Risk Is Dehydration

Diarrhoea and vomiting drain the body of fluids and salts, and dehydration is the main danger. The WHO lists warning signs including unusual drowsiness or lethargy, sunken eyes, being unable to drink or drinking poorly, and skin that returns slowly to normal when pinched. The CDC adds reduced urination, a dry mouth, dizziness on standing, few or no tears when crying, and unusual fussiness in children.

Babies and young children, older adults, people with chronic illnesses, and those with weakened immune systems, including people living with HIV, are at the greatest risk of severe illness. Malnourished children are particularly vulnerable. Globally, diarrhoeal disease is the third leading cause of death in children under five, killing more than 440,000 a year, according to the WHO.

Treatment

There is no specific medicine for viral gastroenteritis, and the CDC notes that antibiotics do not work against viruses. Treatment is about replacing lost fluids. The WHO recommends oral rehydration solution (ORS), sold as sachets at pharmacies and clinics and mixed with clean water. People should continue to drink safe fluids, children should keep eating, and breastfed babies should keep breastfeeding. The WHO also recommends a course of zinc for children with diarrhoea, which can shorten the illness, to be given under the guidance of a health worker.

Medical help should be sought if diarrhoea persists for 14 days or longer, if there is blood in the stool, or if there are signs of dehydration. Severe dehydration may need fluids delivered by drip in a health facility. Anyone caring for a baby, a young child, an older person or someone with a chronic condition who is unwell should not wait.

How Outbreaks Are Investigated

Finding the cause of an outbreak involves several teams working in parallel. Health agencies test samples from sick patients to identify the organisms involved. Water authorities test the supply, and environmental health practitioners inspect water systems, kitchens and food handling. Investigators then compare where and when people fell ill with what they ate, drank and did, looking for the common link.

That process is under way in both cases. In Bronkhorstspruit, the NICD is testing patient specimens, the Department of Water and Sanitation has tested the plant and reservoirs, and the Water Research Commission is conducting an independent investigation. At Rhodes University, the institution says it is working with local public health authorities and environmental health practitioners and has begun testing water at its residences. It reported just over 100 cases among students, a figure some media outlets have put at no fewer than 109. No link between the Makhanda and Bronkhorstspruit cases has been confirmed.

How to Protect Yourself and Your Family

Where tap water is in doubt, the advice is to drink water that has been boiled and cooled, or bottled water, and to use it for cooking, brushing teeth and making ice. The WHO notes that keeping water storage containers covered can reduce faecal contamination at the household level. Residents in the affected parts of Bronkhorstspruit have been told by the government not to use the tap water for drinking, cooking, bathing, brushing teeth or washing clothes, to throw away stored water and disinfect containers with household bleach, and to use only tanker or other safe water.

Hands should be washed with soap and water after using the toilet and before handling food. Fruit and vegetables should be washed with safe water, shellfish cooked thoroughly, and contaminated surfaces cleaned and disinfected. The CDC also recommends washing soiled laundry in hot water. Anyone who is ill should avoid preparing food for others until they have recovered.

This article is general information and not a substitute for medical advice. Anyone who is unwell should speak to a healthcare professional.

FAQ

What is a gastrointestinal outbreak? It is a cluster of stomach and intestinal illnesses in which more people fall ill than expected in the same place and time, usually from a shared source such as contaminated water, food or contact with sick people.

What causes gastroenteritis? According to the WHO, it is usually caused by bacteria, viruses or parasites. Common causes include norovirus, rotavirus, E. coli, Salmonella, Shigella and Campylobacter.

How does contaminated water make you sick? Faeces from people or animals can carry disease-causing germs. When water is not properly treated, those germs end up in what people drink and cook with. Chlorine is widely used in treatment to kill most of them.

How long does norovirus last? The CDC says symptoms usually begin 12 to 48 hours after exposure and most people recover in one to three days. People can still be contagious after they feel better.

How long should I stay home after a stomach illness? The CDC advises staying home until 48 hours after symptoms have stopped.

How do I treat diarrhoea at home? Keep drinking safe fluids and use oral rehydration solution from a pharmacy or clinic. Children should keep eating, and breastfed babies should keep feeding. Antibiotics do not treat viral gastroenteritis.

When should I see a doctor? If diarrhoea lasts 14 days or more, if there is blood in the stool, if there are signs of dehydration such as drowsiness, sunken eyes or being unable to drink, or if the patient is a baby, young child, older person or someone with a chronic condition.

Is the tap water in Bronkhorstspruit safe to drink? Not according to the government. Residents of the affected areas have been told not to drink it, and no timeframe has been given for it to be declared safe.