Why look at post-flood germs as a timeline?

According to a Dailynews report citing Thailand's Department of Disaster Prevention and Mitigation (DDPM) at 06:00 on 5 October 2026, floods were affecting 26 provinces plus Bangkok, with 1,270,151 households affected (source: dailynews.co.th). Water is receding at different times, so each household's risk depends on its own date.

People tend to relax once the house looks clean, yet illnesses such as leptospirosis and hepatitis A have incubation periods long enough to appear after everyone has stopped thinking about the flood, and mold that began on day one often becomes obvious in week two or three.

Example case: one month in Grandma Chan's house

Note: a typical scenario compiled from common post-flood situations, not a real person's account.

Day 1: Grandma Chan, seventy, lives with her daughter and eight-year-old grandson in a single-storey house on the outskirts of Pathum Thani. Waist-deep water stayed for nearly a week. On the day it receded, her daughter waded into the mud in sandals to carry things out and cut her sole on broken glass.

Day 4: the family slept at home although the floor was still damp. The grandson developed diarrhoea, and the daughter's foot wound became red, swollen and throbbing. She went to a clinic for wound care.

Day 10: black spots appeared on the bedroom wall above the old water line and Grandma began coughing at night. The daughter, who had been helping neighbours clean every day, developed a high fever and severe calf pain. The doctor immediately asked about wading in floodwater.

Day 25: things seemed better, until a relative who had shared meals with them during the flood became tired, lost his appetite and noticed yellowing eyes.

The risks came in waves, and knowing each stage would have helped this family act sooner.

How we ranked flood germs by timeline

This is an editorial ranking by the World Health Disinfection (WHD) team, not an official or statistical ranking. Germs are ordered from those to tackle first to those that tend to show up last, weighing:

1. Timing: when each germ typically starts causing problems or symptoms, using general incubation information from CDC and WHO.
2. Link to floods in WHO, CDC and Thai Department of Disease Control guidance.
3. Severity and at-risk groups, especially young children, older adults, pregnant women and people with chronic illness.
4. Ease of spread in crowded homes and shelters.
5. The action each stage requires: wound protection, drying, or watching for delayed symptoms.

Time ranges are general figures from public health agencies and vary between people. This article is not a diagnostic tool. Anyone unwell after floodwater contact should see a doctor and mention that exposure.

Stage 1: days 0 to 3, mud removal and washing

This is when people touch the most water and mud. The main risks come from direct contact and wounds.

No. 1: Sewage bacteria such as E. coli (Escherichia coli) and Shigella

Why it ranks first: these arrive the moment drains and septic tanks overflow, and clean-up day brings the heaviest contact: touching mud then the mouth, eating without washing, using utensils that sat in floodwater. Diarrhoea from this group usually begins within a few days.

Where it hides: mud on floors, grout lines, bathrooms with septic backflow, kitchen cabinets, counters and flood-touched food.

Symptoms and who is at risk: diarrhoea, cramps, nausea, sometimes fever or bloody stools. Young children and older adults dehydrate fast; seek care for bloody stools, drowsiness or inability to drink.

Prevention: rubber gloves, handwashing before every meal, discarding flood-touched food, safe drinking water, and keeping children out of mud and standing water.

Cleaning and spraying: this is not yet the time to spray, because the house is still full of mud. E. coli and Shigella belong to the bacteria group CHEMGENE HLD4H says it covers; organism-specific test data is available from WHD on request.

No. 2: Wound germs such as Staphylococcus aureus, Streptococcus and the tetanus germ (Clostridium tetani)

Why it ranks here: the first clean-up days produce the most cuts from glass, nails, metal sheets and tools. Wounds soaked in dirty water can become infected within days. For tetanus, CDC says symptoms usually start between 3 and 21 days after infection.

Symptoms and who is at risk: swelling, redness, heat, pus, fever, red streaks from the wound, or muscle stiffness and a locked jaw. People with diabetes, older adults and anyone unsure of their tetanus vaccination need extra care.

Prevention: thick-soled boots and heavy gloves, washing wounds with clean water and soap at once, keeping them covered and dry, and asking a doctor about tetanus vaccination.

Cleaning and spraying: wound care is medical, not something spraying replaces. Reducing germs on surfaces after cleaning lowers the chance of wounds meeting them again. Staphylococcus and Streptococcus belong to the bacteria group the product says it covers; we do not claim spraying destroys tetanus spores. Removing all mud is what works there.

Stage 2: days 1 to 7, the first week

People start moving back. Some still share relatives' homes or shelters, food and water are not fully safe, and the house is still wet.

No. 3: Norovirus and rotavirus

Why it ranks here: gut viruses spread fast when people live close together. CDC notes norovirus symptoms usually begin 12 to 48 hours after exposure. Both are non-enveloped, so they resist soap and alcohol gel better than cold viruses.

Where it hides: toilets, taps, door handles, toys, baby bottles, dining tables and spots where someone vomited.

Symptoms and who is at risk: vomiting, watery diarrhoea, cramps and low fever. Young children and older adults dehydrate quickly.

Prevention: soap-and-water handwashing, a separate bathroom for the sick where possible, prompt cleaning of vomit, and boiled or steamed bottles.

Cleaning and spraying: this is when spraying starts to matter, once mud is gone and surfaces are washed. Norovirus is named in CHEMGENE HLD4H product information; rotavirus belongs to the virus group the product says it covers, with specific data available on request.

No. 4: Mold beginning to grow, such as Aspergillus, Penicillium and Cladosporium

Why it ranks here: CDC says mold can begin growing within 24 to 48 hours after materials get wet. The first week decides whether a house develops a serious mold problem.

Where it hides: gypsum walls, plywood, under laminate, mattresses, carpets, curtains, closed wardrobes and cardboard boxes.

Symptoms and who is at risk: stuffy nose, sneezing, coughing, itchy eyes and asthma flare-ups, especially in people with allergies, asthma or weakened immunity.

Prevention: ventilation, fans, dehumidifiers, removing soaked mattresses and carpets, and cutting out wet gypsum as advised by a contractor.

Cleaning and spraying: after removal and washing, spraying treats remaining mold on wall frames and surfaces. Product information states it covers fungi in general; ask for species-specific data.

No. 5: Adenovirus and other causes of red eye

Why it ranks here: conjunctivitis is common after floods because dirty water splashes into eyes and people share towels in temporary housing. Adenovirus is non-enveloped and lasts a while on shared items.

Where it hides: towels, pillowcases, handkerchiefs, TV remotes and door handles.

Symptoms and who is at risk: red, irritated, watery eyes with discharge, sometimes fever or sore throat. Schoolchildren pass it on fast. See a doctor for severe pain or blurred vision.

Prevention: no eye rubbing, frequent handwashing, separate face towels and no shared eye drops.

Cleaning and spraying: wash fabrics as hot as they allow and spray shared touch points. Adenovirus belongs to the virus group the product says it covers but is not named; test data is available on request.

Stage 3: days 8 to 14, the second week

The house looks normal, adults return to work and children to school. This is when illnesses with medium incubation periods begin to show.

No. 6: Leptospira, the cause of leptospirosis (rat urine disease)

Why it ranks here: Thailand's Department of Disease Control warns about leptospirosis after every flood. The bacteria come from the urine of rats and other animals in water and damp soil, and enter through cuts, scrapes or skin softened by long soaking. CDC says symptoms usually start between 2 days and 4 weeks after exposure, so week two is when many people fall ill, just as memories of wading fade.

Where it hides: standing water under raised houses, damp mud, drains, storerooms, warehouses and places with rat activity.

Symptoms and who is at risk: sudden high fever, headache, muscle pain especially in the calves, red eyes. Clean-up crews, volunteers, farmers and anyone who waded for long periods are most exposed. Anyone with fever after wading should see a doctor at once and mention it.

Prevention: boots, no wading with open wounds, showering straight after wading, sealed food storage and rodent control.

Cleaning and spraying: Leptospira is not named on WHD's pages but belongs to the bacteria group the product says it covers. WHO and CDC advise cleaning and then disinfecting flood-contaminated surfaces. Spraying ground floors and storerooms after washing reduces germs on surfaces people touch. Ask for organism-specific test data if needed.

No. 7: Respiratory viruses such as influenza, RSV and SARS-CoV-2

Why it ranks here: after floods, people crowd into small spaces with damp air, little sleep and exhaustion from cleaning, all of which help respiratory viruses spread. The late rainy season in Thailand is already a common time for RSV and influenza.

Where it hides: air in closed rooms, handrails, tables, phones, toys and shared building areas.

Symptoms and who is at risk: fever, cough, sore throat, runny nose and breathlessness. Babies, young children, older adults and people with heart or lung disease face more severe illness; seek care for laboured breathing or a fever that will not come down.

Prevention: masks when sick, open windows, frequent handwashing, separating the sick, and asking a doctor about flu vaccination for risk groups.

Cleaning and spraying: COVID-19, RSV and influenza H1N1 and H5N1 are named in WHD's service and product information, so spraying touch points in homes, offices and schools in week two helps cut surface transmission.

No. 8: Skin and foot fungi such as dermatophytes and Candida

Why it ranks here: early "flood foot" is often irritation from soaking, but if feet stay damp for days, skin fungi move in, so the problem is often clearest in week two.

Where it hides: boots that never dry, socks, doormats, bathroom floors and shared towels.

Symptoms and who is at risk: itching between toes, peeling, soggy skin, odour and red rashes in skin folds. People with diabetes must take foot wounds seriously.

Prevention: wash and dry feet thoroughly, change socks often, dry footwear and stop sharing towels.

Cleaning and spraying: bathroom floors, corridors and shoe areas are worth spraying after washing. These organisms belong to the fungi group the product says it covers; ask for specific data.

Stage 4: week 3 to one month

Many families believe the flood is behind them, yet long-incubation illnesses and accumulated mold show up now.

No. 9: Hepatitis A virus

Why it ranks here: hepatitis A spreads through food and water contaminated by faeces. CDC gives a typical incubation of 15 to 50 days, so someone infected during the flood may only feel ill in week three, at one month or later, and may pass it on unknowingly.

Where it hides: cups, utensils, chopping boards, water tanks, storage jars and bathroom surfaces.

Symptoms and who is at risk: tiredness, poor appetite, nausea, upper-right abdominal pain, yellow skin or eyes and dark urine.

Prevention: boiled water, freshly cooked food, handwashing before food preparation, cleaning water tanks before use, and asking a doctor about vaccination.

Cleaning and spraying: hepatitis A is not named on WHD's pages but belongs to the virus group the product says it covers. Specific data is available on request.

No. 10: Accumulated building mold and melioidosis (Burkholderia pseudomallei)

Why it ranks here: by week three or four, mold not handled in week one has usually spread visibly and the musty smell has set in. Meanwhile, melioidosis bacteria, found in soil and water in many parts of Thailand, especially the Northeast, can cause symptoms from a few days to several weeks after exposure, and occasionally much later.

Where it hides: mold in walls, ceilings, cabinets and wooden furniture; melioidosis bacteria in mud and standing water around homes, rice fields and gardens.

Symptoms and who is at risk: mold keeps allergies and asthma flaring; melioidosis can cause fever, cough, abscesses or wounds that do not heal. People with diabetes or kidney disease and those working in mud are at higher risk and should mention soil and water contact to their doctor.

Prevention: weekly mold checks, removal of affected materials, boots and gloves for soil work, and covered wounds.

Cleaning and spraying: if mold returns, remove and wash first, then spray that area again. Melioidosis in soil is a matter of personal protection; indoor spraying does not treat the ground outside. On surfaces it belongs to the bacteria group the product says it covers; ask for specific data.

Note: dengue from Aedes mosquitoes breeding in water-holding containers also tends to rise in the weeks after floods. It is not a surface germ, but empty containers and remove standing water around the home at the same time.

Summary: flood germs ranked by timeline

An editorial ranking, not official statistics. Time ranges are general.

Why one round of soap or bleach is not enough

• One clean, many waves: scrubbing on day one does not stop mold growing in week two or germs carried home from work.
• Soap lifts dirt but is not designed to destroy every germ; non-enveloped viruses resist it better.
• Bleach is weakened by mud and must never be mixed with ammonia or acidic cleaners, which CDC warns creates dangerous gas.
• Wiping misses spots behind cabinets, under beds and high on walls.
• Bleach does not fix mold inside porous materials; CDC advises removing them.

When to spray: timing WHD disinfection spraying

Following the WHO and CDC principle of clean first, then disinfect, the best time is right after mud removal, washing and removal of damaged materials, which for most homes falls in the first week. Spraying in weeks two to four still helps, especially when new mold appears or illness keeps circulating.

WHD's disinfection spraying service is carried out by trained technicians who, according to the service information, use spraying and/or ULV (Ultra Low Volume) fine-mist fogging. The product is CHEMGENE HLD4H, a UK medical-grade disinfectant containing Benzalkonium Chloride and Didecyldimethylammonium Chloride, described as broad-spectrum against viruses, bacteria and fungi. Named organisms include SARS-CoV-2, Human Coronavirus 229E, RSV, influenza H1N1 and H5N1, HIV, norovirus, hand, foot and mouth virus, vaccinia virus, mycobacteria, Salmonella and Bordetella pertussis. The service page states 99.99% efficacy; the product page states 99.85% against COVID-19 within one minute. The service page cites the Department of Medical Sciences, Mahidol University, NHS England and EN 14476:2013+A2:2019. For other organisms, ask for test data.

1. Survey: water line, date water receded, early mold, septic backflow, vulnerable residents.
2. Clean before spraying: mud out, surfaces washed, damaged materials removed.
3. Zoning: people and pets leave the zone; food, utensils and personal items are put away.
4. Spraying: floors, walls, furniture, bathrooms, kitchens, touch points and corners.
5. Re-entry: about 30 minutes per the service information, always following the technicians' on-site timing.

We do not claim spraying leaves no residue; ask about food-contact surfaces or toddler areas. Anyone unwell should see a doctor, as spraying is not treatment. For musty air, consider residential ozone disinfection. The service includes a free CHEMGENE spray and WELLGIENIC wet tissues, and a tax invoice is available.

10 reasons to spray in the first week after the water recedes

1. Break the chain of gut infections before they pass around the family.
2. Catch mold early, before whole wall panels must go.
3. Reduce germs on ground floors where children and elders walk barefoot.
4. Cover several germ groups at once, per the disinfection service information.
5. Fine mist reaches gaps behind cabinets and under beds.
6. Respiratory viruses named: COVID-19, RSV and influenza.
7. No guessing dilution ratios or risky mixing.
8. A plan for weeks two to four from the technicians.
9. Quick re-entry, about 30 minutes per the service information.
10. Reopen shops and offices with confidence. Talk to WHD.

Before and after timed spraying

Example case: a small tutoring school reopening in week two

Note: an illustrative example, not a real customer review.

Teacher Prae runs a tutoring school in a two-unit shophouse whose ground floor took about half a metre of water. Her staff cleaned the classrooms within three days and she planned to reopen in week two, but children nearby had diarrhoea and colds. The team found a damp carpet in the reading corner, swelling plywood desks and a bathroom that had seen sewage backflow. They advised lifting the carpet, replacing the desks and scrubbing the bathroom, then sprayed classrooms, bathroom and the parents' waiting area on a weekend. A week-by-week checklist, she said, helped most.

Timeline checklist

• Days 0 to 3: power off on flooded floors until checked; boots, gloves, mask; remove mud; discard flood-touched food and medicine; wash every wound; start drying.
• Days 1 to 7: remove soaked mattresses, carpet and gypsum; wash all surfaces; book spraying once clean; clean water tanks; boil drinking water.
• Days 8 to 14: watch for fever, calf pain, red eyes or cough and see a doctor, mentioning wading; dry feet and footwear.
• Week 3 to 1 month: check walls, ceilings and cabinets weekly for new mold; watch for fatigue, jaundice and dark urine; empty water-holding containers.

FAQ

Which day should we spray?
After mud removal, washing and material removal, usually within the first week. Never spray over mud.

It has been a month. Is spraying still worthwhile?
Yes, if new mold appears, illness keeps circulating, or a shop or office is reopening. The team will assess which areas need it.

Why did mold return in week three after scrubbing?
Usually because materials are still damp inside or mold threads are embedded. Find the moisture source and remove damaged parts first.

I have fever and calf pain ten days after helping clean. Is that flood-related?
It may be leptospirosis, which CDC says can start 2 days to 4 weeks after exposure. See a doctor now and mention wading.

Do we need weekly spraying?
Not for most homes. One spray after cleaning, plus drying and rechecks, is usually enough; repeats are case by case.

What if heavy rain floods the house again?
Restart the clock from the latest recession: clean the mud first, then reassess spraying.

Don't let germs arrive in waves. Book spraying once cleaning is done

WHD technicians assess your site, plan around the date your water receded, and spray homes, shops, offices and schools.

See the WHD Disinfection Service

Call 065-556-6294 | LINE @whd268

Related services and references

• WHD disinfection spraying service
• Residential ozone disinfection
• Dailynews, flood update citing DDPM, 5 Oct 2026: https://www.dailynews.co.th/news/6249374/
• CDC, Floods: https://www.cdc.gov/floods/
• CDC, Leptospirosis: https://www.cdc.gov/leptospirosis/
• CDC, Hepatitis A: https://www.cdc.gov/hepatitis-a/
• WHO fact sheets: https://www.who.int/news-room/fact-sheets
• Department of Disease Control, Thailand: https://ddc.moph.go.th/