Flooding: the health consequences

More and more people around the world are affected, perhaps because of climate change, say Lucy Dennison and Mark Keim

Flooding in Bangladesh is a serius social and health problem. Contaminated drinking water may carry cholera or typhoid fever

“This is devastating. Yesterday I had to leave my house as the water rose 1.5 metres in less than 12 hours. People are shocked, scared. Uncertainty is the key word for everybody. At the moment it is raining, and I can’t really describe my feelings, to know it may cause the level of the water to rise more . . . This is out of our hands.”¹

The number of people affected by flooding is increasing globally. In 2007 England had the worst inland flooding for 60 years, leading to an independent inquiry.² Flooding is the most common type of disaster worldwide.³ Trends in climate change have seen an increase in sea levels and an increase in rainfall in many areas of the world,⁴ which may help explain the increase in flooding.

So, what are the health risks associated with flooding? As increasing numbers of people are affected, doctors need to be able to answer this question, not only for disaster relief work abroad but also for hospital and community medicine at home. This is made all the more difficult by a paucity of research in this area and a lack of a central database to register injuries and deaths caused by flooding.

The consequences of flooding are multifaceted. It can affect health directly or indirectly. Signs of ill health may be evident immediately or may only become apparent sometime later, when the flood is all but forgotten. It may affect a person’s physical or mental wellbeing, and often both.

The impact of a flood on people’s lives depends not only on the objective severity of the flood but also on people’s vulnerability and resilience.

Drowning and injuries

Drowning and injuries caused by being in water are the main risks to good health at the time of flooding. The depth of flood water required to cause severe injuries or even drowning can be surprisingly modest. As little as 15 cm of water can knock people off their feet—especially if they are frail—and 60 cm is sufficient to float a car.⁵ Driving vehicles into flood waters is one of the main causes of drowning in rich countries. Flood waters may carry debris or conceal other hazards, such as drains with missing covers and obstacles that are blocking the road. Injuries commonly seen in patients who have been exposed to floods include sprains and strains, lacerations, puncture wounds, abrasions, and contusions (bruising). Open wounds may be contaminated by dirty water. Prolonged exposure in cold water may lead to hypothermia, particularly in young or elderly people.

Transporting supplies in Bangladesh

Infectious diseases

Floods have the potential to increase the transmission of infective diseases. This potential depends on the circumstances of the flood, in particular whether the flood occurs in a high or low income nation. The risk is increased by population displacement, loss of clean drinking water, poor sanitation, poor nutritional status, lack of immunisation, and inadequate access to health care.⁶ Immunisation is not normally indicated after a flood disaster, unless a specific vaccine preventable outbreak occurs.

Flood water may become contaminated with sewage, which can lead to waterborne infections. The risk of a big outbreak is low unless drinking water supplies are affected or there is population displacement. Population displacement can be associated with overcrowding and poor sanitation, which are risk factors for the spread of infection. Outbreaks of diarrhoeal illness occur in high and low income countries after flooding. The causative pathogen is usually endemic to that region. Immediate management involves administering oral rehydration therapy using a solution made by dissolving eight teaspoons of sugar and one teaspoon of salt in a litre of clean (or boiled) water. Other documented outbreaks thought to be caused by contaminated drinking water have included cholera,⁷ balantidiasis (an intestinal protozoan), and typhoid fever. Similarly, these outbreaks occur in regions where the pathogen is endemic.

Vector-borne infections may also occur after floods because of an increase in breeding grounds for vectors, with areas of standing water. Opportunities for mosquitoes to breed may initially be washed away by flooding but will increase as the flood waters ebb. In parts of the world where malaria occurs, an epidemic can lag behind a flood by about 4-8 weeks. Other potential vector-borne infections include dengue and West Nile fever. Flooding may precipitate an increase in rodent-borne infections because the usual patterns of contact alter. Outbreaks of leptospirosis, a bacterial infection, are also well documented in many countries after fresh water flooding.⁸ This is usually spread by exposure to water contaminated by urine from animals, including rats and farm animals.

Respiratory disease

Homes that have been flooded provide a favourable environment for moulds to grow, because of increased moisture. These moulds can cause respiratory infections and allergic or hypersensitivity reactions of the respiratory tract. Exposure to moulds usually occurs during the clean-up after the flood. To avoid exposure, workers should wear a particulate respirator, which will protect them from inhaling potentially dangerous spores.

Psychosocial problems

Flooding often causes devastating personal losses. This may be the loss of a loved one, a livelihood, or a home and personal belongings. Understandably, this can trigger mental health problems in susceptible people. This assumption is supported by evidence that shows that flood exposure is related to increases in depression,⁹ anxiety, and somatic symptoms.¹⁰ Indeed, particularly in Europe, mental health disorders may be the largest public health problem after flooding.

Post-traumatic stress disorder “arises as a delayed or protracted response to a stressful event or situation of an exceptionally threatening or catastrophic nature.” Typical features include episodes of repeated reliving of the trauma in intrusive memories, dreams or nightmares, and avoidance of activities and situations reminiscent of the trauma.¹¹ Evidence shows an association between flood exposure and symptoms of the disorder. One study in New Orleans after hurricane Katrina showed a prevalence in survivors of 19%.¹² It found that predisposing factors for developing the disorder in this sample were varied. Women and people of non-black race were found to be at greater risk. The severity of the flood exposure was also related to the prevalence of the disorder. Knowing someone who died in the disaster; not having property insurance; having had a longer evacuation; having a much longer commute to work compared to before the hurricane; and living in a newly purchased or rented house or in a temporary trailer were identified as risk factors.

Opinion on whether suicide increases after flooding is mixed, and the evidence is poor. Recent evidence from the World Health Organization suggests that reports of suicidal thoughts dropped significantly after hurricane Katrina.¹³ This was attributed to new found faith in one’s ability to rebuild one’s life and realisation of inner strength.

Infrastructure damage

Structural damage to a country has many knock-on effects for the health of individual people. After hurricane Mitch in 1998, the president of Honduras, Carlos Flores Facusse, lamented that the hurricane had set his country back by 50 years.¹⁴

When a region’s transport system is affected by flood waters it makes airports and rail links redundant and turns roads into rivers. The distribution of food is sometimes compromised. Food supply may also be affected by direct flood damage to crops and livestock or to stores of food but rarely causes food shortage. Transport difficulties also compromise emergency relief efforts, preventing rescuers from access to people in need and holding up vital resources, such as water and food.

Floods can reduce the supply of clean water. This is exacerbated if sewage disposal systems are damaged. A lack of clean drinking water can lead to infectious diseases more commonly a result of poor hygiene and the diseases given above. If water supplies are limited then there may not be enough water for washing, leading to poor personal hygiene and sanitation.

If electricity supplies are interrupted, generators may be used by some people to provide electricity until supplies return. The indoor use of generators brings the risk of carbon monoxide poisoning. Symptoms of carbon monoxide poisoning are notoriously easy to miss, but include tiredness, headaches, giddiness, nausea and vomiting, chest pain, breathlessness, stomach pains, behaviour change, and visual problems. In the aftermath of a flood, when electricity supplies have been restored, there is a risk of electrocution during the clean-up. If electricity supplies are lost then heating may also be lost, with the risk of hypothermia.

Disruption of underground pipes and tanks by flood waters may result in the release of toxic chemicals and toxic waste. The effect on health depends on the pollutant. Some pollutants, such as petrol, are highly flammable and can cause explosions and fires. After hurricane Katrina, greater amounts of many toxic chemicals were found in the sediment left after the flood waters receded.¹⁵

Flooding causes enormous disruption to communities and individuals. It affects homes, livelihoods, social networks, and psychological and physical wellbeing. Because flooding is affecting increasing numbers of people, health professionals should have an understanding of its impact on health. This will equip them to give appropriate preventative advice and know what to look for when making diagnoses.

Competing interests: None declared.

Provenance and peer review: Commissioned; externally peer reviewed.

See “Climate change, equity, and health” (Student BMJ 2001;9:402-3, http://student.bmj.com/issues/01/11/editorials/402.php) and “Global warming” (Student BMJ 2004;12:222, http://student.bmj.com/issues/04/06/editorials/222.php).

Lucy Dennison final year medical student University of Bristol
mjk9@cdc.gov
Mark Keim senior science adviser Centers for Disease Control and Prevention, 4770 Buford Highway; MS-F09, Atlanta, GA, USA 30341
Student BMJ 2009;17:110-111 | March

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