Flooding and Communicable Diseases

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Flooding and Communicable Diseases

The major risk ​factor for ​outbreaks ​associated with ​flooding is the ​contamination ​of drinking-​water ​facilities, and ​even when this ​happens, the risk ​of outbreaks ​can be ​minimized if ​the risk is ​well recognized ​and disaster-​response ​addresses the ​provision of ​clean water as ​a priority.

Risk assessment

Floods can potentially increase the transmission of the following communicable diseases:

Water-borne diseases

Flooding is associated with an increased risk of infection, however this risk is low unless there is significant population displacement and/or water sources are compromised. Of the 14 major floods which occurred globally between 1970 and 1994, only one led to a major diarrhoeal disease outbreak - in Sudan, 1980. This was probably because the flood was complicated by population displacement. Floods in Mozambique in January-March 2000 led to an increase in the incidence of diarrhoea and in 1998, floods in West Bengal led to a large cholera epidemic (01,El Tor, Ogawa).

The major risk factor for outbreaks associated with flooding is the contamination of drinking-water facilities, and even when this happens, as in Iowa and Missouri in 1993, the risk of outbreaks can be minimized if the risk is well recognized and disaster-response addresses the provision of clean water as a priority. In Tajikistan in 1992, the flooding of sewage treatment plants led to the contamination of river water. Despite this risk factor, no significant increase in incidence of diarrhoeal diseases was reported. A typhoon in Truk District, Trust Territories of the Pacific in 1971 disrupted catchment water sources and forced people to use many different sources of groundwater that were heavily contaminated with pig faeces. As a result, there was an outbreak of balantidiasis, an intestinal protozoan. A cyclone and flooding in Mauritius in 1980 led to an outbreak of typhoid fever.

There is an increased risk of infection of water-borne diseases contracted through direct contact with polluted waters, such as wound infections, dermatitis, conjunctivitis, and ear, nose and throat infections. However, these diseases are not epidemic-prone.

The only epidemic-prone infection which can be transmitted directly from contaminated water is leptospirosis, a zoonotic bacterial disease. Transmission occurs through contact of the skin and mucous membranes with water, damp soil or vegetation (such as sugarcane) or mud contaminated with rodent urine. The occurrence of flooding after heavy rainfall facilitates the spread of the organism due to the proliferation of rodents which shed large amounts of leptospires in their urine. Outbreaks of leptospirosis occurred in Brazil (1983, 1988 and 1996), in Nicaragua (1995), Krasnodar region, Russian Federation (1997), Santa Fe, USA (1998) Orissa, India (1999) and Thailand (2000). It is likely that environmental changes increased the vector (rodent) population which facilitated transmission.

Vector-borne diseases

Floods may indirectly lead to an increase in vector-borne diseases through the expansion in the number and range of vector habitats. Standing water caused by heavy rainfall or overflow of rivers can act as breeding sites for mosquitoes, and therefore enhance the potential for exposure of the disaster-affected population and emergency workers to infections such as dengue, malaria and West Nile fever. Flooding may initially flush out mosquito breeding, but it comes back when the waters recede. The lag time is usually around 6-8 weeks before the onset of a malaria epidemic.

The risk of outbreaks is greatly increased by complicating factors, such as changes in human behaviour (increased exposure to mosquitoes while sleeping outside, a temporary pause in disease control activities, overcrowding), or changes in the habitat which promote mosquito breeding (landslide, deforestation, river damming, and rerouting).

Risk posed by corpses

Contrary to common belief, there is no evidence that corpses pose a risk of disease "epidemics" after natural disasters. Most agents do not survive long in the human body after death (with the exception of HIV -which can be up to 6 days) and the source of acute infections is more likely to be the survivors. Human remains only pose health risks in a few special cases requiring specific precautions, such as deaths from cholera or haemorrhagic fevers.

However, workers who routinely handle corpses may have a risk of contracting tuberculosis, bloodborne viruses (such as Hepatitis B/C and HIV), and gastrointestinal infections (such as rotavirus diarrhoea, salmonellosis, E. coli, typhoid/paratyphoid fevers, hepatitis A, shigellosis and cholera).

The public and emergency workers alike should be duly informed to avoid panic and inappropriate disposal of bodies, and to take adequate precautions in handling the dead (see prevention below).

Other health risks posed by flooding


Preventive measures

Communicable disease risks from flooding can be greatly reduced if the following recommendations are followed.

Short-term measures

Chlorination of water

Ensuring uninterrupted provision of safe drinking water is the most important preventive measure to be implemented following flooding, in order to reduce the risk of outbreaks of water-borne diseases.

Vaccination against hepatitis A
Malaria preventiontiger-mosquito-49141_960_720.jpg
Health education
Handling corpses

For workers that routinely handle corpses

Long term measures

Legislative/administrative issues

Technical issues


Gayer M & Connolly MA. Chapter 5: "Communicable Disease Control After Disasters" in Public Health Consequences of Disasters, 2nd edition, eds. Noji, EK. Oxford: Oxford University Press, 2005 (in revision).

Morgan, O. Infectious disease risks from dead bodies following natural disasters. Pan Am J Public Health 15(5) 307-312.

Source: WHO