A sinus-flushing device used to relieve colds and allergies has been linked to a deadly brain-eating amoeba.
Louisiana's state health department issued a warning about neti pots - which look like mini watering cans, that are used by pouring salty water through one nostril.
It follows two recent deaths - a 51-year-old woman and a 20-year-old man from the 'brain-eating amoeba' Naegleria fowleri.
It is thought the amoeba entered their brains when they used the devices.
Both victims are thought to have used tap water, instead of distilled or sterilised water as recommended by the manufacturers.
Dr Raoult Ratard, Louisiana State Epidemiologist, said: 'If you are irrigating, flushing, or rinsing your sinuses, for example, by using a neti pot, use distilled, sterile or previously boiled water to make up the irrigation solution.
'Tap water is safe for drinking, but not for irrigating your nose.'
He added that it is important to rinse the irrigation device after each use and leave open to air dry.
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The very rare infection typically occurs when people go swimming or diving in warm freshwater lakes and rivers.
In very rare instances, health experts said such infections may also occur when contaminated water from other sources, such as from an inadequately chlorinated swimming pool or when people irrigate their sinuses with devices like neti pots.
Naegleria fowleri (centre) and coloured images showing stained samples in brain tissue
Naegleria fowleri (left) and a stained sample seen in brain tissue
According to The Department of Health and Hospitals in Louisiana, the amoeba causes the disease primary amebic meningoencephalitis, a brain infection that leads to the destruction of brain tissue.
In its early stages, symptoms may be similar to symptoms of bacterial meningitis and can include headache, fever, nausea, vomiting and stiff neck. Later symptoms include confusion, loss of balance, seizures and hallucinations.
After the start of symptoms, the disease progresses rapidly and usually causes death within one to 12 days.
A spokesman from the United States Centers for Disease Control and Prevention, said the Louisiana cases are still being investigated.