The 2026 Floods: Why Germs Matter More Than People Think

According to Thailand's Department of Disaster Prevention and Mitigation, in a report published by Dailynews as of 06:00 on 5 October 2026, flooding had affected 26 provinces plus Bangkok, with 1,270,151 households affected. Recovery is exactly when germ exposure peaks, as people return, shovel mud and touch soaked surfaces.

Floodwater is not clean rainwater. It flows through drains, septic tanks, animal pens and rubbish. When it drains away, the liquid goes but silt, grease and some of the germs stay behind on floors, lower walls, corners, pipes and absorbent materials such as wood, fabric, mattresses and carpet. That is why WHO and the CDC give the same core advice: clean flood-contaminated surfaces first, then disinfect them, and dry everything as fast as possible to limit mold.

A Typical Scenario: A House That Looked Clean, and a Family That Kept Getting Sick

Note: this is an illustrative scenario based on situations that commonly follow floods. It is not the account of a specific customer.

Ton works in an office and lives in a two-storey house beside a canal in Pathum Thani with his retired parents and his five-year-old daughter. This year the water came in at shin height and stayed for almost a week. The family carried what they could upstairs and moved in with relatives.

When the water receded, Ton shovelled out the mud, pressure-washed, mopped with scented cleaner, ran fans and moved everyone back on day four. Within two weeks his daughter had diarrhoea, his mother had similar symptoms, his father was coughing every morning and Ton's own toes were red and itchy. Looking again, he found damp silt behind the kitchen cabinets, a black ring around the bathroom drain, mold spots behind the sofa and toys rinsed only with plain water back on the floor. A house that looks clean is not necessarily free of germs.

How We Ranked the Top 10 Germs After Floods (Editorial Criteria)

To be clear from the start: this is WHD's editorial ranking. It is not an official ranking and it is not based on statistics. We did not use case counts or percentages. We weighed five criteria:

1. How often it appears in flood guidance from WHO, the CDC and the Department of Disease Control.
2. Severity.
3. Who is at risk: everyone, or mainly children, older adults, pregnant women and the chronically ill.
4. Persistence in the environment, described qualitatively, never with unsourced survival times.
5. Ease of spread via hands, surfaces, food, water and air.

Use the ranking to prioritise cleaning and prevention. It is not a diagnosis. Anyone who feels unwell after a flood should see a doctor.

No. 1: E. coli and Faecal Bacteria (Escherichia coli)

Why it ranks first: E. coli lives in human and animal intestines and is the standard indicator that water has been contaminated by sewage. Whenever floodwater passes septic tanks, sewers or livestock areas, it brings this group of bacteria with it. It tops the list because it is the most widespread, and its presence usually means other faecal germs are present too.

Where it hides: bathroom floors, around toilets, floor drains with backflow, under the kitchen sink, tile grout, the bottom of door frames and silt left in corners.

Symptoms and risk groups: most E. coli are harmless, but some types cause diarrhoea, cramps, nausea and sometimes bloody stools. Young children and older adults are more likely to become dehydrated or develop complications.

Prevention: wash hands with soap after touching mud or floodwater, drink safe or boiled water, wear rubber gloves and boots while cleaning, and throw away any food that touched floodwater.

How cleaning and spraying help: remove mud and organic residue first, since germs shelter inside it. Spraying then spreads disinfectant evenly over large areas. E. coli belongs to the bacteria group that CHEMGENE HLD4H states it covers, according to product information. If you need test data for this specific organism, ask WHD.

No. 2: Leptospira, the Cause of Leptospirosis

Why it ranks second: Thailand's Department of Disease Control warns about leptospirosis every flood season. The bacteria come from the urine of rats and other animals, survive in standing water and damp mud, and enter through cuts, scratches, water-softened skin, eyes and mouth. It is less common than E. coli, but the potential severity is much higher.

Where it hides: standing water under raised houses, in garages and yards, drains, wet rubbish, and places where rats climbed to escape the water such as storerooms, ceilings and behind cabinets.

Symptoms and risk groups: sudden high fever, headache, muscle pain especially in the calves, and red eyes. Anyone with these symptoms after wading or cleaning should see a doctor quickly and mention flood exposure. Those at highest risk are frequent waders, volunteers, farmers and people cleaning without boots.

Prevention: avoid wading; if you must, wear boots and cover wounds. Shower straight after contact with floodwater, and remove rubbish and food sources that attract rats.

How cleaning and spraying help: draining standing water and drying floors removes the conditions the bacteria need. Washing then spraying surfaces rats may have crossed reduces contamination where people touch. Leptospira is a bacterium within the group the product says it covers; we do not cite organism-specific test results here, and you can request more information.

No. 3: Norovirus and Rotavirus, the Fastest-Spreading Diarrhoea Viruses

Why they rank third: these viruses are major causes of acute diarrhoea and spread through faeces, vomit, hands and contaminated surfaces. A very small amount can make someone ill, and they move quickly through crowded homes, shelters and schools, especially when toilets are not working properly and clean water is short.

Where they hide: door handles, taps, toilet flush buttons, light switches, stair rails, dining tables, children's toys and bathroom floors with backflow.

Symptoms and risk groups: vomiting, watery diarrhoea, stomach cramps and sometimes fever. Babies and young children can dehydrate fast, as can older adults. See a doctor if someone becomes drowsy, passes little urine or does not improve.

Prevention: wash hands with soap for at least 20 seconds, give a sick person a separate bathroom if possible, clean up vomit immediately while wearing gloves, and ask a doctor about age-appropriate vaccines for children.

How cleaning and spraying help: norovirus is one of the organisms CHEMGENE HLD4H lists, according to product information. Rotavirus falls within the virus group the product says it covers; ask WHD if you need rotavirus-specific data. Spraying shared touch points after cleaning helps break the chain of household spread.

No. 4: Indoor Molds (Aspergillus, Penicillium, Cladosporium, Stachybotrys)

Why fourth: mold is the most visible post-flood problem. WHO and the CDC advise drying or removing wet materials within 24 to 48 hours, but many homes sit in water for days and moisture soaks deep into walls, timber and furniture. It is found in almost every flooded home and affects breathing over the long term.

Where it hides: lower gypsum and plaster walls, behind wardrobes, under mattresses, fabric sofas, carpets, wooden door frames and inside air conditioners.

Symptoms and risk groups: stuffy nose, sneezing, cough, irritated eyes and skin; asthma and allergies may flare. People with weakened immunity should not clean heavily molded areas themselves.

Prevention: ventilate, run fans or dehumidifiers, remove soaked materials, wear a fine-particle mask and gloves, and never paint over damp or moldy walls.

How cleaning and spraying help: remove visible mold and dry materials first; spraying then deals with residual mold on surfaces. WHD's service information says the disinfectant covers fungi; ask for species-specific test data. For musty air, residential ozone disinfection can be added.

No. 5: Salmonella and Shigella, Food Poisoning and Dysentery Bacteria

Why fifth: fridges lose power, food spoils, kitchenware sits in dirty water and drinking water is unreliable. Salmonella comes from animal intestines and sewage; Shigella passes easily from person to person on hands. The Department of Disease Control always lists diarrhoea and food poisoning among flood diseases to monitor.

Where they hide: chopping boards, knives, dishes, shelves, flooded fridges, water containers and prep counters.

Symptoms and risk groups: fever, cramps and diarrhoea, sometimes bloody stools with Shigella. Children, older adults and people with weak immunity face higher risk.

Prevention: discard food that touched floodwater, wash then disinfect dishes, throw away wooden boards and cracked containers, cook thoroughly.

How cleaning and spraying help: Salmonella is listed by CHEMGENE HLD4H per product information; Shigella falls within the bacteria group the product says it covers. Spraying kitchens after degreasing lowers cross-contamination risk; rinse food-contact surfaces as the technician advises.

No. 6: Staphylococcus aureus and Streptococcus, Wound Infection Bacteria

Why sixth: injuries from glass, nails, roofing sheets and timber are common during clean-up, and wounds exposed to dirty water can become infected, leading to boils, pus or cellulitis. The CDC treats post-flood wound care as a key topic.

Where they hide: on skin, towels, bed linen, cleaning tools, reused gloves and frequently touched surfaces.

Symptoms and risk groups: a wound that turns red, hot, swollen or pus-filled, or fever. People with diabetes and older adults are at greater risk. Deep soil-contaminated wounds also carry a tetanus risk, so ask a doctor about vaccination.

Prevention: thick gloves and closed shoes, wash wounds at once, use waterproof dressings, see a doctor for deep or inflamed wounds.

How cleaning and spraying help: spraying does not treat wounds, but it reduces bacteria on surfaces everyone touches. These belong to the bacteria group the product says it covers; ask WHD for specific data.

No. 7: Skin Fungi and Candida, Behind Immersion Foot

Why seventh: sore, peeling feet from wading are extremely common. Waterlogged skin is irritated first; if it stays damp, dermatophytes and Candida move in. Less severe than the top six, but very widespread.

Where they hide: wet shoes, socks, doormats, bathroom floors, shared towels and boots reused while damp.

Symptoms and risk groups: soggy white skin between the toes, itching, flaking and cracks. People with diabetes need extra care.

Prevention: wash and dry between the toes after wading, change socks often, do not share towels, ask a doctor or pharmacist early.

How cleaning and spraying help: spraying bathroom floors and barefoot zones reduces fungal transfer within a family; the service information states the disinfectant covers fungi.

No. 8: Respiratory Viruses: Influenza, RSV and SARS-CoV-2

Why eighth: they do not arrive in floodwater, but floods coincide with the rainy season, evacuees crowd together and tired bodies resist infection less well. WHO notes that crowding after disasters raises respiratory infection risk.

Where they hide: airborne droplets and shared items such as phones, remotes, rails, tables and door handles.

Symptoms and risk groups: fever, cough, sore throat and aches. RSV can make young children breathe hard; older and chronically ill people risk lung complications.

Prevention: masks when ill or crowded, handwashing, ventilation, separate personal items, and ask a doctor about flu vaccination.

How cleaning and spraying help: this is the group WHD's service information names most clearly: COVID-19, RSV, H1N1 and H5N1. Spraying shared touch points before moving back or reopening is well targeted.

No. 9: Hepatitis A Virus

Why ninth: it spreads through food and water contaminated with faeces, and WHO links it to poor sanitation and unsafe water, conditions floods can create. People can spread it before they feel ill. It is less common than ordinary diarrhoeal illness.

Where it hides: bathrooms, food containers, untreated water and food handlers' hands.

Symptoms and risk groups: tiredness, nausea, upper-right abdominal pain, yellow skin and eyes, dark urine. People with existing liver disease should be especially careful.

Prevention: boiled or properly bottled water, handwashing before cooking, thorough cooking, and ask a doctor about vaccination.

How cleaning and spraying help: the virus is fairly hardy, so cleaning then disinfecting bathrooms and kitchens matters. It belongs to the virus group the product says it covers but is not named on the service page; ask WHD for test data.

No. 10: Enteroviruses, the Cause of Hand, Foot and Mouth Disease

Why tenth: common in young children in the rainy season, it spreads through saliva, mucus, blister fluid and faeces. After floods, children are confined together, toys are shared and childcare centres reopen.

Where they hide: toys, bottles, feeding spoons, play mats, cots and play areas.

Symptoms and risk groups: fever, mouth ulcers and blisters on palms, soles and buttocks, mainly under fives. Drowsiness, repeated vomiting or unusual neurological signs need a doctor immediately.

Prevention: frequent handwashing, keep sick children home, clean toys daily.

How cleaning and spraying help: hand, foot and mouth virus is named in WHD's service information. Spraying playrooms and childcare centres after cleaning fits well; children stay out during spraying and return at the advised time.

Honourable Mentions

Vibrio (coastal tidal floods), Burkholderia pseudomallei (melioidosis, soil and mud, especially in the north-east), Clostridium tetani (deep wounds), Legionella (stagnant building water systems) and Klebsiella or Pseudomonas (clinics, weak immunity). The rule is the same: protect yourself, clean, dry, then disinfect.

Why Soap or Bleach Alone Often Falls Short

Soap and detergent are essential because they lift the mud and grease germs hide in, but cleaning reduces germs rather than inactivating them. Home bleach use has limits too: people wipe floors and visible stains and miss lower walls, handles and switches; dilutions are often too strong or too weak; surfaces are wiped dry before the required contact time; mixing bleach with ammonia or some toilet cleaners releases dangerous gas, as the CDC warns; leftover dirt weakens any disinfectant; and a fresh scent is not proof that germs are gone. Hence the order: clean, dry, then disinfect, with trained technicians closing the gaps.

WHD Post-Flood Disinfection Spraying: Removing and Helping Prevent the Top 10 Germs After Floods

World Health Disinfection provides a disinfection spraying service for homes, condos, offices, schools, shops and buildings. According to the service information, trained technicians spray and/or ULV-fog (Ultra Low Volume fine mist) using CHEMGENE HLD4H, a medical-grade disinfectant from the UK containing Benzalkonium Chloride and Didecyldimethylammonium Chloride.

The service page describes it as broad-spectrum against viruses, bacteria and fungi, naming COVID-19, RSV, H1N1, H5N1 and hand, foot and mouth virus, with a stated 99.99% efficacy. The product page adds norovirus, Salmonella, Bordetella pertussis and fungi among others. Listed references include Thailand's Department of Medical Sciences, Mahidol University, NHS England and EN 14476:2013+A2:2019. For ranked germs not named on those pages, we make no organism-specific claim: they belong to the bacteria, virus or fungi groups the product says it covers, and you can ask WHD for test data.

The Five-Step Process

1. Survey: assess the flood line, surfaces and hotspots linked to each ranked germ.
2. Mud removal and washing: mud must be cleared, surfaces washed and reasonably dry first. Spraying follows cleaning; it never replaces it.
3. Zoning and preparation: people and pets leave the zone; food, dishes and personal items are put away; non-essential appliances are switched off.
4. Spraying: technicians cover surfaces to plan, focusing on shared touch points and high-risk spots, using ULV where even coverage is needed.
5. Re-entry: the service information says to wait about 30 minutes before normal use; always follow the re-entry time the technicians give for your job and ventilate as advised.

Please note: we do not claim the disinfectant leaves no residue. Food-contact surfaces and toys that small children put in their mouths should be wiped or rinsed with clean water as the technician advises. Anyone who is ill should see a doctor; spraying treats spaces, not people. Promotion per the service information: a free CHEMGENE spray bottle and WELLGIENIC wet tissues with the service, and a tax invoice is available.

10 Reasons to Choose WHD After a Flood

1. The spraying plan follows the risk ranking, not guesswork.
2. Medical-grade CHEMGENE HLD4H from the UK, per the service information.
3. Broad-spectrum coverage of viruses, bacteria and fungi, matching the variety of flood germs.
4. Named organisms including COVID-19, RSV, H1N1, H5N1, hand, foot and mouth virus, norovirus and Salmonella.
5. Fine ULV mist reaches wide areas more evenly than hand wiping.
6. Short downtime: about 30 minutes per the service information. See service details
7. References listed: Department of Medical Sciences, Mahidol University, NHS England, EN 14476.
8. Experience across hospitals, schools, malls, airports, offices, airlines, banks and residential buildings.
9. Honest process: mud first, people out during spraying, re-entry on time.
10. Easy contact and free extras: call 065-556-6294 or LINE @whd268. Request a quote

Before and After

Example Case: Ton's House, Second Time Around

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

Back in Pathum Thani, Ton started again with a plan: he pulled out the kitchen cabinets to remove hidden silt, scrubbed drains, threw out the molded sofa and dried the house for several days. The spraying technician then marked priorities by rank: bathroom and drains, the garage where water had pooled, handles and rails, lower walls, and the playroom. The family waited outside, returned at the stated time and rinsed counters and toys before use. What changed most, Ton says, is that he finally knows what he is dealing with.

Recovery Checklist

Before spraying

• Wear boots, rubber gloves, a mask and goggles while cleaning.
• Remove all mud, including behind and under furniture.
• Wash surfaces with water and detergent, then let them dry.
• Discard food, medicine and cosmetics that touched floodwater.
• Remove soaked, heavily molded items such as mattresses, carpet and gypsum board.

After spraying

• Re-enter at the stated time and ventilate.
• Rinse food-contact surfaces and children's toys as advised.
• Keep controlling humidity so mold does not return.
• Watch for fever, calf pain, diarrhoea, rash or cough, and see a doctor if they appear.

FAQ: Top 10 Germs After Floods

Is this an official ranking?
No. It is WHD's editorial ranking based on the criteria above and on WHO, CDC and Department of Disease Control guidance, not on case statistics.

Why isn't leptospirosis number one?
Our criteria also weigh how often a germ is found. Faecal bacteria turn up in virtually every flooded home; leptospirosis is more severe, so it sits second and deserves equal caution.

Can spraying replace mud removal?
No. Mud and dirt must be removed first; disinfectants work best on clean surfaces.

Does the disinfectant cover all ten?
The product states coverage of viruses, bacteria and fungi and names specific organisms such as COVID-19, RSV, H1N1, H5N1, hand, foot and mouth virus, norovirus and Salmonella. For the others we make no organism-specific claim; ask WHD for documents.

Do we have to leave during spraying?
Yes. People and pets leave the zone and return at the technician's stated time, about 30 minutes per the service information.

You Know the Top 10. Let WHD Help Remove Them.

Mud is out. The next step is disinfection spraying by trained technicians using CHEMGENE HLD4H, per the service information.

Book Post-Flood Disinfection Spraying

Call 065-556-6294 | LINE @whd268

Related Services and References

• WHD disinfection spraying service
• CHEMGENE HLD4H disinfectant
• Residential ozone disinfection for musty air
• Dailynews, DDPM flood report as of 06:00, 5 Oct 2026: https://www.dailynews.co.th/news/6249374/
• WHO fact sheets: https://www.who.int/news-room/fact-sheets
• CDC floods: https://www.cdc.gov/floods/
• Thailand Department of Disease Control: https://ddc.moph.go.th/