Severe Flooding in South Asia: Health Risks and Disease Concerns

• Thailand:  
  
  Cyclone Senyar brought torrential rainfall and widespread flooding and landslides across southern Thailand, prompting a large-scale emergency response. More than two million people have been displaced by the flooding. The Songkhla providence is the most affected, especially Hat Yai city, where floodwaters reached up to 2.5 meters (8.2 feet) in depth. Sikarin and Hat Yai hospitals remain flooded and are facing power outages and limited medical supplies. Water levels have begun receding as of Nov. 27, and ongoing clearance and recovery operations are likely to last through mid-December.  
•  Indonesia:  
  
  Severe weather associated with the passage of Cyclone Senyar has been reported across Indonesia in early December. Heavy rainfall triggered severe flooding and multiple landslides across parts of Aceh, North Sumatra, and West Sumatra provinces from Nov. 23-30. An estimated 570,000 people have been displaced to temporary shelters, causing overcrowding and increasing the risk of acute respiratory infections, water-, and vector-borne disease outbreaks. Regional health services are operational and able to respond to emergencies; however, facilities are facing increasing constraints due to high demand. The Ministry of Health and local authorities are warning about the risk of post-flood diseases and have deployed medical teams and vaccination units to several evacuation centers. Flooding has damaged roads and bridges, making it difficult for rescue teams to reach affected communities.
• Sri Lanka:  
  
  Cyclone Ditwah and associated heavy rainfall from late November caused widespread flooding, landslides, and damage to critical infrastructure across the Central, Eastern, Northwestern, Northern, Sabaragamuwa, Southern, Uva, and Western provinces. The cyclone crossed the country between Nov. 27 and Nov. 29, before dissipating in the Bay of Bengal. Large populations have been displaced and are now living in temporary shelters with limited access to clean water and sanitation. Flood waters at Peradeniya, Kandy, and  Mayiyangana hospitals are expected to recede soon. Initial reports highlight injuries from landslides and flooding, along with growing concerns about leptospirosis. The Sri Lanka Red Cross Society has deployed more than 3,500 volunteers to deliver first aid and distribute water, hygiene supplies, bedding, and clothing. Relief operations remain constrained by road closures and the ongoing risk of secondary landslides.
• Malaysia:  
  
  Between Nov. 22-27, heavy rainfalls from Cyclone Senyar occurred in northern Malaysia. Areas most affected include Kelantan, Terengganu, Kedah, Perlis, and Sarawak regions. Flooding and related disruptions are ongoing across parts of north and central Malaysia as of Nov. 28. Flooding has displaced 18,700 people, with three fatalities reported so far. Localized flooding has disrupted transport and essential services, adding strain to communities already burdened by economic pressures and recent climate-related shocks.  

The recent flooding in Thailand, Indonesia, Sri Lanka, and Malaysia follows months of severe weather across Southeast Asia, including typhoons that struck the Philippines and Vietnam, causing frequent and prolonged flooding in other areas.  

• Water and Sanitation Risks
  
  Contaminated floodwaters and mud remain a significant public health threat. Floodwater poses multiple infectious risks, including bacteria, parasites, and environmental pathogens. These risks increase when river water, sewage overflow, soil, and animal waste mix during flooding, and any open wounds exposed to contaminated water are at a heightened risk for rapid progressive infection. In the coming weeks, many communities may continue to experience a lack of safe water and sanitation facilities. Without safe supplies, outbreaks of cholera, typhoid, dysentery, and hepatitis A become likely. Digestive illnesses, such as norovirus, can also spread through contaminated food and water, particularly in crowded shelters where access to potable water and safe food is scarce.  
• Mold and Respiratory Health Risks
  
  As homes and buildings dry out, mold growth is intensifying respiratory health risks, particularly for those with asthma or other respiratory conditions. In overcrowded shelters, poor ventilation and exposure to dust and debris increases the likelihood of acute respiratory infections, especially among children and the elderly.  
• Infectious Disease Risks  
  
  The combination of stagnant water, poor sanitation, and disrupted healthcare will sharply increase the risk of water-, food-, and vector-borne disease transmission. Cholera, leptospirosis, and diarrheal diseases are primary concerns, while mosquito breeding in floodwaters threatens to worsen vector-borne disease outbreaks/activity. Overcrowding and limited hygiene facilities in shelters further facilitate disease spread among displaced populations. Power outages that interrupt refrigeration compound these risks by compromising food safety.  
• Healthcare Disruptions  
  
  Damaged infrastructure and overburdened systems will delay the resumption of routine and emergency services. Supply chain disruptions can also interrupt the delivery of medicines and medical supplies, with downstream effects far from the disaster zone. Damage to facilities, medication shortages, and cold-chain failures threaten the treatment of chronic conditions such as diabetes, hypertension, cancer, and kidney disease. The lifesaving treatments used to manage these conditions generally demand consistent, reliable access to care and monitoring.  
• Mental Health and Psychosocial Impacts  
  
  The psychological impact of displacement, loss, and uncertainty can lead to anxiety, depression, and post-traumatic stress disorder. Access to mental health and psychosocial support is frequently limited in the immediate aftermath, yet psychosocial support is vital for both immediate recovery and long-term resilience. Health workers are similarly at risk of burnout due to resource shortages and continuous emergency operations.  

This report presents the most up-to-date information available on Dec. 3.  

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