Thailand sees rising risks of summer illness in extreme heat

During periods of hot weather and soaring temperatures, the impact goes beyond discomfort and a sense of being overheated. It also accelerates the growth of many types of disease-causing pathogens, making infectious diseases a common public health concern, especially gastrointestinal illnesses, skin diseases and heat-related disorders.

In Thailand, illnesses linked to hot weather are showing an upward trend, particularly heat-related illness and gastrointestinal disease. According to the latest 2026 data from the Digital Disease Surveillance (DDS) system, the figures are as follows:

Heat-related illness: as of March 18, 2026, 36 cases had been reported nationwide
Food poisoning: from January 1 to March 17, 2026, cumulative cases totalled 39,233
Acute diarrhoea: from January 1 to March 17, 2026, cumulative cases reached 274,151, with two deaths

Understanding how these illnesses develop, recognising dangerous warning signs and following proper medical prevention principles are therefore crucial to helping everyone get through this summer safely and in good health.

Getting to know the infectious diseases that come with summer

Assoc Prof Dr Nopporn Apiwattanakul, of the Division of Infectious Diseases, Department of Paediatrics, Faculty of Medicine Ramathibodi Hospital, Mahidol University, explained in an article on the Rama Channel website that once summer begins, environmental changes directly affect both human life and the growth of microorganisms. Higher temperatures allow many pathogens to incubate and multiply rapidly, increasing the risk of illness.

How pathogens spread

Hot and humid weather creates ideal conditions for bacteria in food to multiply. Heat also causes natural water sources to evaporate or dry up, increasing the concentration of pathogens in each drop of water. When people drink such water or use it to wash ingredients without proper disinfection, pathogens can enter the body more easily. Bacteria and fungi also grow well when sweat accumulates on the body, and moisture builds up under poorly ventilated clothing.

Groups that need especially close monitoring for complications

Although summer infections can affect anyone, some groups need particularly close care and observation because they face a higher risk of severe complications:

• Young children and infants, whose immune systems are not yet fully developed and who lose water faster and in greater amounts than adults
• Older people, who often have a reduced sense of thirst and may become dehydrated without realising it
• People with chronic illnesses such as diabetes, kidney disease and heart disease, who may develop severe complications when infection occurs
• People who work outdoors for long periods, who face both greater exposure to environmental pathogens and a higher risk of heatstroke

Common food- and water-borne diseases during summer

“One of the most common health problems during the summer is gastrointestinal disturbance, mainly caused by eating food and drinking water contaminated with pathogens or toxins.”

Cholera and severe diarrhoea from contaminated food

Cholera is caused by bacterial infection from contaminated food or drinking water. Its most distinctive symptom is large-volume, continuous watery diarrhoea resembling rice water. Some patients may also vomit. Without prompt treatment and fluid replacement, the body can lose water and electrolytes severely, leading to shock, kidney failure and death within a matter of hours. Nowadays, this disease is less common.

Food poisoning, a silent threat from rapidly multiplying bacteria

Hot and humid weather causes food to spoil more quickly than usual. Bacteria that cause food poisoning can multiply rapidly in a short time when food is left at room temperature. Patients often experience abdominal cramps, nausea, vomiting and diarrhoea, usually soon after consuming food contaminated with toxins produced by bacteria.

Hepatitis A, a danger linked to eating raw food

Hepatitis A is a food- and water-borne disease, especially associated with consuming raw or undercooked seafood such as oysters and cockles, or fresh fruit and vegetables that have not been cleaned properly. Early symptoms resemble the flu, including fever, fatigue and loss of appetite, followed by jaundice, yellowing of the eyes, dark urine and pain beneath the right rib cage. The disease can be effectively prevented through good hygiene and vaccination.

Skin infections caused by damp conditions

It is not only food and drink that become a problem. Higher temperatures and frequent weather changes also inevitably affect the respiratory system and skin health.

“Summer flu”: different from the common cold and heat exhaustion

“Summer flu” often occurs when the body cannot adjust quickly enough to sudden temperature changes, such as walking in from intense outdoor heat into a very cold air-conditioned room. Patients may develop fever, headache, fatigue and body aches, but they will not usually have nasal congestion, sore throat or a runny nose like a cold caused directly by a virus. Resting in a well-ventilated place and drinking enough water can help symptoms gradually improve.

Rabies, a nearby danger that can be prevented by vaccination

During summer, mammals such as dogs and cats are more likely to become stressed and irritable, leading to a higher number of bites and scratches. Rabies is a serious infectious disease with a fatality rate of nearly 100% once symptoms appear. If bitten or scratched by an animal, the wound should be washed immediately with soap and clean water for at least 10 to 15 minutes. A doctor should then be seen for rabies vaccination and tetanus risk assessment. For those at greater risk of dog or cat bites, such as young children who like to play with pets, parents may consider pre-exposure rabies vaccination in advance.

Fungal infection and pustules caused by trapped sweat

In hot weather, the body produces a large amount of sweat to release heat. If tight-fitting or poorly ventilated clothing is worn, moisture builds up, creating the kind of environment in which fungi and bacteria on the skin thrive. This can lead to itchy rashes, ringworm, tinea versicolor, or bacterial infection of the hair follicles, causing inflamed pustules. Prompt bathing, proper cleansing with soap after heavy sweating, and wearing loose, breathable clothing are therefore the best forms of prevention.

Danger signs that require urgent medical attention

Monitoring abnormal symptoms is extremely important because some infectious diseases can spread quickly and damage the body’s systems in a short time. If any of the following warning signs appear, people should not ignore them or buy medicines to treat themselves.

Severe dehydration in children and older people

Dehydration is the most dangerous and common complication of diarrhoea and vomiting. Warning signs that the body is severely dehydrated and requires medical attention include:

• Dry, cracked lips; dry skin with poor elasticity that does not spring back when pinched
• Extreme thirst, or conversely, marked lethargy to the point of being unable to drink
• Greatly reduced urination, very dark urine, or no urination at all for more than four to six hours
• Sunken eyes; in infants, a noticeably sunken fontanelle
• Crying without tears, rapid heartbeat, deep laboured breathing, and a weak, fast pulse

Septic shock from bloodstream infection

If the immune system is weakened, or if a person is infected with highly aggressive bacteria, pathogens from the gastrointestinal tract or from wounds may enter the bloodstream, leading to severe infection throughout the body. Symptoms that require emergency hospital care include very high fever, chills, increasing drowsiness, confusion, incoherent responses, rapid breathing, low blood pressure, cool, pale skin and possible loss of consciousness. Without prompt treatment with intravenous antibiotics, organ failure and death may follow.

Prevention and behavioural adjustment for safety

Prevention is always better than treatment. Small changes in daily behaviour can create a strong protective barrier and effectively reduce the risk of summer infections.

The hygiene rule: hot food, serving spoons and handwashing

Basic hygiene is the first and most important line of defence against gastrointestinal disease.

• Eat hot food: choose freshly cooked food that has been heated thoroughly. Avoid raw or undercooked food, dishes left out too long, and ice that does not meet proper standards.
• Use serving spoons: Use a separate serving spoon every time food is shared with others, to prevent viruses and bacteria from spreading through saliva.
• Wash hands: wash hands with soap and clean water for at least 20 seconds before preparing food, before eating, and after using the toilet every time.

Choosing and storing food properly in hot weather

Ingredients should be bought from clean and reliable sources. Check the colour, smell and freshness of meat and seafood. Cooked food should not be left at room temperature for more than two hours, or more than one hour on very hot days. If food is not finished, it should be refrigerated immediately and reheated until boiling or piping hot throughout before being eaten again. Foods containing coconut milk require particular caution because they spoil very easily and should not be kept overnight.

Strengthening the immune system to cope with hot weather

Maintaining good health from within helps the immune system function at full capacity. People should drink enough clean water, at least eight to 10 glasses a day, to replace fluid lost through sweat. They should eat all five food groups, especially properly washed fresh fruit and vegetables for vitamins and minerals, get enough sleep, avoid outdoor activities during the hottest hours between 10am and 3pm to reduce the risk of dehydration and heat exhaustion, and receive appropriate vaccinations.

Summer infectious diseases, whether gastrointestinal illness or skin problems, are common threats that come with extreme heat and environmental conditions that favour the growth of pathogens. However, the severity of these illnesses can be prevented and managed quite easily through attention to personal hygiene, choosing clean and freshly cooked food, maintaining the body’s fluid balance, and regularly watching for abnormalities in oneself and family members. If severe symptoms such as dehydration, persistent vomiting or high fever occur, medical attention should be sought immediately for proper assessment and treatment, so that everyone can stay safe and healthy throughout the season.