A typical scenario: home from the shelter, and the whole lane gets sick

In a neighbourhood along Khlong U-Taphao in Hat Yai, Songkhla, days of heavy rain sent water rushing into homes. Fon's family, with a three-year-old son, a seven-year-old daughter, her husband and her diabetic mother, spent almost a week at a temporary shelter in a nearby school. Hundreds of evacuees shared a handful of toilets, clean water for handwashing was scarce, and the children played with the same donated toys.

When the water went down, everyone rushed home to shovel mud, wash floors and start cooking again. Just two days later, Fon's youngest developed a fever and cramping stomach pain. He cried every time he used the toilet, and his stool contained mucus and blood. The next day her daughter had diarrhoea, then her mother. Meanwhile, the lane's LINE group filled with messages from three other households whose children were "sick the same way".

At the hospital, the doctor sent stool samples for culture. The result was bacillary dysentery caused by Shigella. The family received oral rehydration salts and appropriate treatment, along with firm advice about handwashing with soap, not sharing personal items and cleaning the bathroom, because this germ passes from person to person very easily. Local health officers also came to investigate the cluster.

Fon was left wondering how to stop the germ circulating in her home. What about the toys that had soaked in floodwater? How thoroughly should the shared bathroom and the nappy-changing corner be cleaned? This article explains Shigella dysentery after floods, how it moves through families and communities, and a step-by-step plan to restore the home, with ozone disinfection as the final step after physical cleaning.

Note: this is an illustrative scenario based on problems commonly seen after floods. It does not describe a real, identifiable person.

Understanding Shigella: a tiny dose, a big outbreak

Dysentery means inflammation of the large intestine that causes diarrhoea with mucus or blood. Amoebic dysentery is caused by a parasite, while bacillary dysentery is caused by bacteria, chiefly Shigella species such as Shigella sonnei, Shigella flexneri and Shigella dysenteriae. Shigella lives mainly in the human gut, so the source is the stool of people who are ill or who have recovered but are still shedding bacteria.

What makes Shigella so troublesome after a flood is how few bacteria it takes to cause illness. The US CDC notes that swallowing only a very small number of germs can make someone sick. A hand that looks clean, a shared towel or a toy another child has just mouthed can be enough. That sets it apart from germs that need a heavy dose from badly contaminated food or water.

How it spreads after the water recedes

• Person to person via hands. The main route. Someone uses the toilet or changes a nappy, washes poorly, and bacteria reach door handles, taps, water dippers, remote controls, phones and food.
• Contaminated water and food. Septic overflow during the flood, uncovered water jars, vegetables rinsed in dirty water and food cooked by someone who is ill.
• Shared items. Hand towels, bath towels, cups, spoons, toys and bedding in shelters or crowded homes.
• Flies. Rubbish and waste left behind after a flood attract flies, which can carry bacteria from faeces onto food.
• Crowding and water shortages. During evacuation and the first days home, handwashing with soap is inconsistent, so infections appear in clusters.

Symptoms

Symptoms usually start one to two days after exposure, sometimes a little later:

• Frequent loose stools, watery at first, later with mucus or blood.
• Cramping stomach pain and a painful urge to pass stool even when little comes out.
• Fever, weakness, nausea and sometimes vomiting.
• Some young children with high fever have seizures, which needs hospital care immediately.
• Symptoms often improve within about a week, but bacteria can still be shed in stool for some time afterwards.

When to see a doctor: bloody stool, high fever, severe pain, vomiting that prevents drinking, little urine, a dry mouth, drowsiness or a seizure in a child all mean going to hospital straight away. Older adults, young children and people with chronic illness should not wait. Meanwhile, sip oral rehydration salts (ORS) often to prevent dehydration. Do not give anti-diarrhoeal medicine to children or anyone with bloody diarrhoea without medical advice, as it can keep bacteria in the gut longer. Antibiotics are a doctor's decision. If there is fever with calf pain after wading through floodwater, tell the doctor, because leptospirosis is common at the same time.

Who is most at risk

• Children under five, the group most often affected, because they mouth objects, cannot wash their own hands well and wear nappies.
• Carers and nursery staff, who change nappies and help children in the toilet many times a day.
• Older adults, who dehydrate quickly and may develop kidney problems or low blood pressure.
• Pregnant women, for whom dehydration and high fever affect both mother and baby.
• People with chronic illness or weak immunity, such as diabetes, kidney disease, cancer or HIV.
• People in crowded settings such as shelters, dense neighbourhoods, dormitories or homes where several related families move in together after a flood.

Why dysentery spreads like a chain reaction after a flood

Picture one household. The first child falls ill. Mum changes a nappy, rinses her hands quickly with plain water, then slices fruit for the older sibling. The older child eats it, then plays with the neighbour's kids, sharing snacks and the same toys. The next day the neighbour's child is sick, and that child's mother cooks a pot of food for relatives who came to help clean. The chain keeps growing.

Several post-flood factors speed it up: exhaustion that makes people skip handwashing, limited soap and clean water, bathrooms whose drainage has not recovered, relatives and volunteers moving between many houses, large pots of food from community kitchens and donated items passed from hand to hand without cleaning.

What communities can do together

Because Shigella moves between households, one clean house is not enough if the lane keeps passing it around. Communities recovering from a flood can agree on a few simple habits: soap and water at every shared toilet and at community kitchens, with someone responsible for refilling them; cooks who have had diarrhoea stepping away from food preparation until a doctor clears them; volunteers washing their hands before leaving one house and entering the next; donated toys and bedding cleaned before being handed out; and rubbish and waste collected quickly so flies have less to feed on. When several households report bloody diarrhoea at the same time, informing the local health office early allows officers to investigate the source and give targeted advice before the cluster grows.

Hot spots inside the home

• Bathroom and toilet: flush handle, seat, rim, bidet spray, taps, water dipper and door handle are the most contaminated points.
• The nappy-changing corner: changing mats, floor mats, the nappy bin and the surrounding floor.
• Children's toys: especially ridged plastic toys, rubber squeeze toys and soft toys that soaked in floodwater.
• Kitchen and dining table: chopping boards, knives, dishes and table cloths, where hands meet food.
• Fabrics and bedding: towels, sheets, pillowcases and soiled clothing.
• Shared touch points: light switches, remotes, stair rails, phones, children's tablets and fridge handles.

The impact when dysentery circulates at home and in the community

• Health: young children and older adults dehydrate quickly, and some need intravenous fluids and a hospital stay. When family members fall ill one after another, the carers wear down too.
• Money: treatment for several people, ORS, replacement nappies and supplies, and lost income while parents stay home, on top of flood repair costs.
• Time: children miss school until they recover and a doctor or school says they can return, adults miss work, and house repairs stall.
• Reputation and community ties: a household with cases may be blamed, food stalls must pause, nurseries close temporarily and trust between neighbours is shaken.
• Family strain: parents feel guilty, older relatives with chronic conditions can decline, and stress from the flood and the illness piles up.

Why the usual responses fail to stop the outbreak

• Rinsing hands with plain water. Water alone does not remove the germs. Rub hands with soap for at least twenty seconds, especially after the toilet, after nappy changes and before preparing food.
• Relying on alcohol gel instead of soap. Gel is convenient but does not replace soap and water in every situation, particularly when hands are visibly dirty.
• Cleaning the bathroom once after the flood. While someone is ill, the bathroom and touch points need cleaning daily, more often if several people are sick.
• Sharing hand towels. One damp towel is a direct bridge from one person to the next.
• Pouring bleach on muddy floors. Organic matter in mud weakens disinfectants, so surfaces must be cleaned first. Never mix cleaning products.
• Spraying air freshener in the bathroom. The smell fades for a while, but the germs stay, and the family assumes the room is clean.
• Giving flood-soaked toys straight back. Toys with ridges, hollow cavities or fabric are very hard to clean thoroughly.

Breaking the dysentery chain takes both behaviour, above all handwashing with soap, and systematic environmental cleaning. Once the house is clean and dry, a whole-room disinfection step helps deal with the places hands and cloths miss.

WHD ozone disinfection: closing out home recovery after an outbreak

World Health Disinfection (WHD) provides residential and building ozone disinfection for homes, condominiums, hotels, offices, factories, schools and hospitals. Ozone (O3) is a strongly oxidising gas. Released in a sealed space, it spreads throughout the room, behind the toilet, under the basin, into cabinet gaps, under beds and into furniture crevices that are hard to wipe. It breaks down the cell structures of bacteria, viruses and mould and breaks apart odour molecules, then reverts to oxygen (O2) with no chemical residue.

According to the test results the company has had certified by Thailand's Department of Medical Sciences and Intertek (UK), WHD's process eliminates 99.99% of viruses, bacteria and mould. See the certification page for details.

Ozone's proper role: treatment comes after mud removal, washing and drying. It does not replace handwashing with soap, daily bathroom cleaning or medical care. Anyone with bloody stool, fever or signs of dehydration must see a doctor. Ozone reduces germs left in the environment across the whole room, giving the home a fresh start once patients recover and lowering the chance that the environment passes germs back to the family.

Timing matters. The most useful moment for ozone treatment is when the mud is gone, surfaces have been washed with detergent, soaked items have been sorted or discarded, and the house has dried out. At that point the treatment is not fighting against layers of silt and damp, and it can work on what remains on walls, ledges, fixtures and furniture. For families who have just been through an outbreak, many choose to book it once the last patient is feeling better, so the whole household can move back into shared rooms together.

How the service works

1. Assessment. The team asks how many people were ill and which rooms they used, including bathrooms, the nappy corner, children's rooms and the kitchen, then plans the zones.
2. Preparation. Everyone, including pets and plants, leaves the zone. Food is removed, cupboards and drawers are opened, washed toys are spread out, and doors and windows are sealed.
3. Ozone release. The generator runs at a concentration matched to the room. No person or animal may be inside.
4. Contact time. Ozone works on the air and surfaces, typically about 30 minutes per zone.
5. Rest and ventilation. The machine is switched off, the ozone reverts to oxygen and windows are opened. The team tells you when re-entry is safe.
6. Handover. Advice on a bathroom cleaning schedule, separate towels and child-height handwashing stations.

Safety reminder: ozone is used only in an empty, closed space. People, pets and plants must be out, and nobody re-enters until the rest and ventilation period is complete.

10 reasons a home that had dysentery cases should consider ozone

1. Covers the whole bathroom. Behind the toilet, under the basin, window ledges and vents are all reached in a sealed room.
2. Suits children's rooms and nappy corners. Ozone reverts to oxygen, leaving no chemical residue where children crawl and sleep. Read about ozone and chemical residue removal.
3. Certified test results. According to testing certified for the company by the Department of Medical Sciences and Intertek, 99.99% of viruses, bacteria and mould are eliminated.
4. Tackles bathroom and flood odours. Odour molecules are broken down rather than masked.
5. Short cycles. Around 30 minutes per zone, scheduled around the rooms you need first.
6. Limits post-flood mould. Done once the house is dry, it helps with mould starting in bathrooms and damp walls.
7. Marks a fresh start. A clear milestone that tells the family the home is ready for normal life after everyone recovers.
8. Works for community spaces. Nurseries, classrooms, shared toilets and community halls can also be treated. See the residential and building ozone service.
9. Pairs with touch-point spraying. Combine it with WHD's disinfection service.
10. Good value. Ozone jobs of 15,000 baht or more include a free medical-grade disinfectant spray for daily bathroom touch points.

Before and after home recovery

Example case: a community nursery in Nonthaburi

This example case is an illustrative scenario reflecting common situations. It is not a review from a specific customer.

Pui runs a small community nursery by the river in Pak Kret, Nonthaburi, caring for about thirty children aged two to five. After the ground floor flooded for ten days, teachers and parents cleaned it together and reopened. Within the first week several children had diarrhoea, some with blood in their stool. Health officers investigated and confirmed a Shigella outbreak.

The nursery closed temporarily on official advice, and sick children were treated and kept at home. The team threw out all soft toys and hollow toys, washed hard plastic toys one by one, replaced the changing mats, scrubbed the children's toilets and tightened the handwashing routine. Once everything was completely dry, they booked WHD to ozone-treat the classroom, nap room, toilets and nappy area on a closed day when nobody was inside.

Pui says parents regained confidence because every step was explained openly, from discarding toys and changing handwashing habits to ozone as the last step. The nursery reopened when officials advised it was ready, children who had been ill returned on medical advice, and staff kept wiping toilet touch points daily with the free medical-grade spray from the promotion.

Checklist to break the dysentery chain at home

While someone is ill

• Wash hands with soap and clean water for at least twenty seconds after the toilet, after nappy changes and before preparing or eating food. Help young children every time.
• The sick person should not prepare food for others until recovered and cleared by a doctor.
• If possible, give the patient a separate toilet, or clean the bathroom after each use.
• Keep separate hand towels, bath towels, cups and spoons for each person.
• Seal used nappies in a bag before disposal and clean the changing mat after every use.
• Wash soiled laundry separately, hot if possible, and dry it fully.
• Give ORS frequently and seek care immediately for danger signs.
• Keep sick children away from school, nursery and swimming pools until a doctor or the school says they can return.

Before ozone

• Finish mud removal and washing while wearing rubber gloves, boots and a mask.
• Discard soft toys, hollow toys that took in water and cushions that soaked up floodwater. Wash hard plastic toys.
• Clean the bathroom and all touch points with a cleaner first, then apply disinfectant according to the label.
• Dry the house thoroughly. Health agencies generally advise starting cleaning and drying within 24 to 48 hours after the water recedes to limit mould.
• On treatment day, move all people, pets and plants out, and open cupboards and drawers.

After ozone

• Re-enter only when the team confirms the rest and ventilation period is over.
• Set up a handwashing station with soap at child height, with a reminder sign.
• Keep cleaning bathroom touch points daily for several more weeks.
• Watch everyone for symptoms. If a new case appears, see a doctor and inform local health officers.

Frequently asked questions

1. How is Shigella dysentery different from ordinary diarrhoea?

It typically brings fever, cramping, a painful urge to pass stool and diarrhoea with mucus or blood, and it spreads easily because a small number of bacteria can cause illness. Diagnosis needs a doctor and a stool test.

2. After ozone, can we stop handwashing or daily bathroom cleaning?

No. Handwashing with soap is the core of prevention. Ozone reduces germs in the environment at the time of treatment, but while anyone is ill or still shedding bacteria, the bathroom and touch points need daily cleaning.

3. Should we treat while someone is still sick, or after recovery?

Ideally after physical cleaning and drying, once patients are improving, as a fresh start. If treatment is needed earlier, the patient must rest in another zone or stay elsewhere. Nobody may be inside a zone being treated.

4. Can flood-soaked toys be used again after ozone?

Soft toys and hollow toys that took in water should be discarded. Hard plastic toys should be washed with soapy water and dried first. Ozone is an extra step to reduce remaining surface germs and musty smells.

5. Can nurseries and classrooms use this service?

Yes. WHD serves homes and buildings, including schools. Book on a closed day, and follow health officers' advice about when to reopen.

6. How long do we need to stay out?

About 30 minutes per zone, plus a rest and ventilation period. The team will confirm the safe re-entry time based on the actual size and number of zones.

Break the chain and start again in a cleaner home

Cleaned and dried? Let WHD finish with ozone disinfection of your bathrooms, children's rooms, kitchen and every space you worry about.

Book Post-Flood Ozone Disinfection

Call 065-556-6294 · LINE @whd268 · Email worldhealthdisinfection@gmail.com

Related services and reading

• Residential and building ozone disinfection
• Full disinfection service
• Ozone cleaning service
• Contact WHD

References

• US CDC: hygiene and clean-up after a flood
• World Health Organization: diarrhoeal disease fact sheets