After wading in floods, fever within 14 days needs a doctor

The water has gone down, the furniture is back in place and life is about to return to normal. Then, about a week later, a high fever starts, with a headache and calf pain so bad it is hard to walk. Many people assume it is a cold from days in the rain, buy fever pills and go to bed. But a fever like this after wading through floodwater may be leptospirosis, and the later you see a doctor, the greater the risk of serious illness.

Plenty of Thais have caught the disease this year. Dr Montien Kanasawat, director-general of the Department of Disease Control, released figures in late September showing 3,303 leptospirosis cases and 46 deaths between 1 January and 23 September 2026, Bangkok Biz News and Thansettakij reported. That means about 1.4 of every 100 patients died, and since early July weekly case numbers have mostly been above the median of the past five years.

Heavy rain in the South from 7 to 9 November makes this a time for extra care

This week the risk comes closer for people in the South. Advisory No. 7 from the Thai Meteorological Department warned of heavy to very heavy rain in the South from 7 to 9 November, and told people to watch for flash floods, overflowing rivers and landslides, especially in homes near waterways at the foot of hills and in low-lying areas. When floods come, people have to wade to work, to the shops or while moving their things to safety, and water that stands for days is where the leptospirosis germ lives.

Ranong, Trang and Nakhon Si Thammarat, all in the South, are three of the five provinces with high rates this year, along with Nan and Mae Hong Son. The most cases are among people aged 60 and over, followed by those aged 50 to 59 and 40 to 49. The occupation with the most cases is farming, since farmers already work in wet fields and orchards almost every day.

The germ comes from animal urine and enters through cuts and water-softened skin

Leptospirosis is caused by bacteria shed in the urine of infected animals: not only rats, but also dogs, cattle, buffalo, pigs, goats and sheep. When their urine mixes into floodwater or mud, the germ can enter the human body through cuts, through skin softened by soaking, and through the lining of the eyes, nose and mouth.

Think of your fingertips after a long soak, wrinkled and soft. Skin like that keeps germs out less well than dry skin, so soaking in water for about 3 hours or more, or having scrapes on your feet and legs, raises the chance of infection. Small wounds you have not noticed, such as a scratch or a blister from your shoes, are a way in too.

What makes the disease dangerous is the wait. Symptoms usually start 5 to 14 days after exposure, and in some people up to 30 days. By the day the fever starts, many people have forgotten they ever waded through water.

Protection starts with your first step into the water

The best protection is to avoid wading or soaking when you do not need to. If you must go into the water, the Department of Disease Control advises wearing rubber boots and covering any wounds with waterproof plasters first. If you have no boots, clean plastic bags pulled over your feet and legs will do. When you get out, wash your hands, legs and body with soap and clean water straight away, and do not stay in clothes wet with floodwater.

At home you can cut off the rats too. Keep food and drinking water in sealed containers, and deal with rubbish so rats cannot feed on it. After the water goes down, wear boots and rubber gloves when cleaning the house or moving things that were under water, because the mud left behind can still carry the germ. If you are in an evacuation shelter and have suspicious symptoms, tell the shelter's health officer.

If you get a fever after wading, see a doctor and say you were in floodwater

The symptoms to watch for are high fever, headache, muscle pain especially in the calves, thighs or back, and red eyes. Some people also have nausea, vomiting or diarrhoea. If you have these symptoms after wading or soaking in water, see a doctor quickly and tell them you were in floodwater, because that helps the doctor think of leptospirosis sooner. If you start to feel short of breath, find it hard to breathe, your skin or eyes turn yellow, or you pass less urine, the illness has become critical and you need to go to hospital at once.

Most patients who died saw a doctor too late, and buying medicine to take yourself can make the illness worse. That includes preventive medicine such as doxycycline, an antibiotic many people have heard can be taken before wading. It is used at a doctor's discretion, only for high-risk people such as those who have to stay in water for long periods, flood volunteers and people who collect rubbish or animal carcasses after floods. People should not buy it for themselves, because the medicine does not fully prevent infection, and pregnant women, breastfeeding women, children under 8 and anyone with drug allergies need a doctor's assessment first. Even if you have taken the medicine, a fever still means seeing a doctor and saying you waded through water.

Before the heavy rain reaches the South on Saturday, 7 November, there are three things you can do today. First, put rubber boots or clean plastic bags, waterproof plasters and soap by the door. Second, note in your phone the dates you wade through water, so that if a fever starts in the next 5 to 14 days you can tell the doctor straight away. Third, save the Department of Disease Control's 1422 hotline for questions about the disease and how to prevent it.

Sources

• Bangkok Biz News: อย่า ซื้อยาป้องกันโรคฉี่หนูกินเอง มีอาการรีบไปพบแพทย์ แจ้งประวัติสัมผัสน้ำ
• Thansettakij: เปิดวิธีสังเกต 5 อาการเตือนโรคไข้ฉี่หนู ภัยร้ายหน้าฝนและน้ำท่วมขัง
• Real News Thailand: เตือนช่วงปลายฝนต้นฤดูหนาวเฝ้าระวังป่วยด้วยโรคไข้ฉี่หนู
• Thai Meteorological Department: Variable weather in upper Thailand and heavy to very heavy rains in the South No. 7