The invisible threats after fresh water flooding

South C flooded
The South C area of Nairobi under water. Photo: Twitter/MichaelMutuma

It seems like everytime we turn on the news there is a report of flooding. Less than an hour ago reports of five people dying, four of them kids, as Texas is once again hit by heavy rain and flooding.

Nairobi has been hit by flash floods that have claimed almost two dozen lives across the city. The death toll is predicted to rise further with 69 people still unaccounted for who are thought to be in the rubble of a collapsed building the flood waters brought down. This is just a couple of weeks into the ‘long rains‘ that will last until mid June.

As if the loss of life and property isn’t enough the invisible threats that arrive with freshwater flooding…as opposed to salt water/ocean flooding, will make a desperate situation much, much worse.

There are several diseases and a myriad of other health concerns that go hand in hand with freshwater flooding, and living in the First World doesn’t make you any safer than the Nairobians in Kenya. The floodwaters are likely to be full of debris which can cause injury but it’s what’s lurking unseen in the water that can cause problems even after the floods have subsided.


The force of moving water is irresistible and it’s not only people that are swept away. Chemicals, even when stored properly in non-flood conditions are likely to get into the water. Some, such as petroleum products are visible as a slick or film on the surface of the water, others are totally invisible. Caustic substances, solvents, inks, paints and anything else you can think of are going to be mixed into the flood waters and even though they will be massively diluted in such a high volume of liquid but they’re still there and will cause major problems if ingested. Some heavier than water toxins will collect in depressions as the floodwaters recede and those puddles, magnets for children, will contain much higher levels of toxins in the residues left behind as the waters evaporate.


Power lines, particularly in those areas where electricity cables are supported by wood telegraph style poles, can be a major hazard. Electricity can arc a considerable distance and lines in standing water can electrify a large area.


Water is an irresistible force and flowing water can move a huge amount of debris ranging from lumps of concrete to vehicles. Standing water can hide major hazards that can make moving through it particularly dangerous.Getting a cut or graze when moving through flood water can lead to life threatening infections within days. Cuts also allow other diseases easy access into your body.


Leptospirosis is a zoonotic disease, it can be passed from an animal species to man. Rodents carry leptospirosis and anything that brings them into closer than usual contact with humans poses a potential for infection. The flooding occurs rats and mice will alway seek out drier ground in which to nest. As rats and mice are incontinent they leave a trail of urine wherever they go and until this urine is totally dry it is able to pass leptospirosis to humans via cut, grazes and abrasions on the skin. Andy Holmes the British Olympic rower died of leptospirosis in 2010. He had a small graze on his finger and it’s thought that’s how he contracted the disease. He had been rowing on the River Severn a few days before he first became sickened with a flu like illness. He went into kidney failure and died some time later.

When clearing up after a flood event be sure to cover cuts and grazes with waterproof plasters. Wear waterproof gloves and preferably thick soled boots to protect your feet and ankles. Long trousers are a must. If you get a cut when cleaning up after a flood, stop what you’re doing, squeeze the cut to force as much contamination as possible out of the wound, wash the area and cover with a clean waterproof dressing.

Typhoid Fever

Caused by the bacteria Salmonella typhi, typhoid fever is a life threatening illness. People infected with typhoid carry the bug in their intestines and shed it in their faeces. Ingesting food or drink prepared by a typhoid suffer can pass on the disease unless they have scrupulous hand hygiene. Salmonella typhi gets into floodwaters where sewers overflow and pipes fracture. Once it’s in the flood water food contamination is highly likely, either by people getting it on their skin and then preparing food, or by food supplies getting contaminated directly by the water. Contaminated water getting into the fresh water supply is a major source of infection. Typhoid still sees sporadic outbreaks across Africa and the recent flooding is likely to cause an increase in cases.


Vibrio cholerae is a rapid onset intestinal disease that is immediately recognisable by the victim producing massive amounts of watery diarrhea and profuse vomiting. Without rapid medical intervention death can occur in just a few hours due to massive dehydration and shock.

As with typhoid consuming contaminated food and drink . Cholera gets into the water and can contaminate food and the skin of those who prepare food. Flood waters getting into drinking water supplies will spread the disease rapidly amongst those using the source for drinking or food preparation.


A world wide disease that causes tens of millions of infections each year across the globe. As animals as well as humans carry the bacteria that causes the disease it will certainly be present in any flood waters where animals have defecated or when human waste has gotten into the floodwaters. As with any flooding contamination of drinking water is commonplace. particularly in areas where wells or boreholes are used for drinking water.

Necrotising Fasciitis

This is a horrendous condition commonly called ‘the flesh eating bug’ in the media. It’s rare but is one of the most awful diseases I have ever dealt with. the most common bacteria to cause the disease is Staph A group of bugs. Doctors advise that those with cuts and abrasions should not use whirlpools, hot tubs etc unless the wound is well covered with a completely waterproof dressing. Hot tubs are spotless compared to floodwaters.


There are several types of malaria, some more serious than others with Plasmodium falciparum and Plasmodium vivid being the most serious. Malaria is spread by the Anopheles mosquito, only the females spread the disease. standing water is a mosquito magnet, they lay their eggs in water and just a teaspoon of water can contain hundreds of larvae.

It’s when the floods subside and small puddles are left that mosquitoes will seek out these puddles to lay their eggs. If you get enough bites your body becomes used to them and you no longer itch and the bites often produce no bump which means people are oblivious to the fact that they have been bitten and thus increases the risk of having malaria for some days before seeking medical assistance.

The list of illnesses that are caused by waterborne pathogens is a long one, way beyond the scope of one article.