As Malaysia enters the Northeast Monsoon season from November 2025 to March 2026, the country braces for weeks of heavy rainfall and strong winds.

While this seasonal shift brings cooler temperatures and replenishes water resources, it also creates an environment conducive to the spread of infectious diseases. The monsoon period is closely associated with a surge in waterborne, vector-borne and airborne illnesses, forming a trifecta of health threats that require urgent public awareness and preventive action.

The Malaysian Meteorological Department has forecast several episodes of intense rainfall during this monsoon, particularly affecting states such as Kelantan, Terengganu, Pahang, Johor, Sarawak and Sabah. These downpours often lead to flooding, which disrupts daily life and damages infrastructure.

Health implications of floods

However, the health implications of these floods are equally concerning. Stagnant water and contaminated floodwaters become reservoirs for pathogens, increasing the risk of outbreaks in affected communities. When water systems are compromised and sanitation facilities are overwhelmed, the likelihood of disease transmission rises significantly.

Vector-borne diseases, particularly dengue, remain a major public health challenge during the monsoon. Stagnant water in clogged drains, discarded containers and puddles provides ideal breeding grounds for mosquitoes.

Malaysia recorded more than 122,000 dengue cases in 2024, and although early 2025 has shown a decline, the risk persists throughout the rainy season. The presence of Aedes mosquitoes in both urban and rural areas means that even short periods of neglect in eliminating breeding sites can lead to a rapid increase in cases.

Dengue not only causes severe illness but also places a heavy burden on healthcare facilities, making prevention a critical priority.

Waterborne diseases also surge during floods.

Leptospirosis, commonly known as rat fever, becomes more prevalent when floodwaters are contaminated by rodent urine. Communities exposed to these waters face heightened risks, especially when wading through flooded areas without protective gear.

Typhoid and cholera outbreaks are additional concerns when clean water supplies are disrupted. These illnesses can spread quickly in flood-affected regions, particularly where access to safe drinking water and proper sanitation is limited. The consequences are severe, ranging from prolonged hospitalisations to fatalities, underscoring the importance of preventive measures.

Airborne diseases, particularly respiratory infections, also increase during the monsoon.

Influenza-like illnesses and severe acute respiratory infections are closely monitored by health authorities, as damp conditions and crowded shelters facilitate transmission.

Recent data indicate that consultations for influenza-like illnesses and hospital admissions for severe respiratory infections remain significant, highlighting the need for vigilance.

Vulnerable groups, including children, the elderly, and individuals with chronic conditions, are at greater risk of complications, making early detection and treatment essential.

Globally, monsoon seasons are associated with spikes in disease incidence across South and Southeast Asia. Climate variability and extreme weather events exacerbate these trends, creating additional challenges for public health systems.

Need for proactive measures to mitigate risks

Malaysia’s experience reflects a broader regional pattern, where health authorities must adapt to seasonal fluctuations in disease prevalence. The interplay between climate and health is becoming increasingly evident, and proactive measures are necessary to mitigate these risks.

Preventive strategies are the cornerstone of reducing the impact of monsoon-related diseases.

Individuals should avoid contact with floodwaters whenever possible and ensure that drinking water is boiled or treated during periods of flooding. Maintaining cleanliness in and around homes to eliminate mosquito breeding sites is vital. Good respiratory hygiene, including the use of masks in crowded areas and proper ventilation indoors, can help curb the spread of respiratory infections. Seeking prompt medical attention for symptoms such as fever, cough, or unusual fatigue is equally important to prevent complications. These measures, though simple, can significantly reduce the burden of disease during the monsoon season.

The Northeast Monsoon is an annual phenomenon, but its associated health risks can be mitigated through collective action. Public awareness campaigns, community engagement, and adherence to health guidelines are key to safeguarding lives during this season.

By prioritising preventive measures and remaining vigilant, Malaysians can manoeuvre the challenges of the monsoon while minimising the threat posed by waterborne, vector-borne and airborne diseases.

The responsibility lies not only with health authorities but also with individuals and communities. Together, proactive steps can transform the monsoon from a season of vulnerability into one of resilience.

-- BERNAMA

Dr Rafidah Lani (rafidah@um.edu.my) is a Senior Lecturer at the Department of Medical Microbiology, Faculty of Medicine, and an Associate Researcher at the Ungku Aziz Centre for Development Studies, Universiti Malaya.