Johnny Jackson, a 10-year-old American boy from South Carolina, died at home on Sunday from “dry drowning” more than an hour after going swimming and walking home with his mother. The sad event highlights a little known danger that parents and child carers should be aware of, that drowning can kill hours after being submersed in water.

Johnny’s mother, Cassandra Jackson, told NBC News in a story broadcast on the TODAY show on Thursday that:

“I’ve never known a child could walk around, talk, speak and their lungs be filled with water.”

Johnny must have got some water in his lungs while he was swimming in his local pool at Goose Greek, South Carolina. He didn’t show any signs of respiratory distress, but he had an accident in the pool and “soiled himself”, said the TODAY report. He then walked home with his mother and sister.

His mother said she bathed him and he told her he felt sleepy. When she went to check on him later she saw his face was covered in a “spongy white material”. He was rushed to hospital but it was too late.

According to the latest figures, about 3,600 Americans died from drowning in 2005, said the US Centers for Disease Control and Prevention (CDC), including a small percentage that die up to 24 hours later because of water entering the respiratory system. A not insignificant number of the victims are children who died after having a bath.

Dr Daniel Rauch, pediatrician at New York University Langone Medical Center, who spoke to Meredith Vieira on the TODAY show, said there are three important signs that parents and carers should look out for: difficulty breathing, extreme tiredness, and changes in behaviour. All three symptoms result from the brain not getting enough oxygen because of water in the lungs.

It would seem that Johnny was showing two of these: tiredness and change in behaviour (the soiling accident in the pool). Rauch expressed sympathy for parents, because it is very difficult to spot these symptoms in children, especially small children, who can change mood very quickly and get tired easily from rushing around and playing.

However, if your child has these symptoms and has been swimming, you should take him or her to an emergency department to get checked out. If there is water in a lung, the doctors put a tube into the lung and force oxygen through under pressure. The lung then heals itself in time.

Drowning is a significant cause of disability and death, wrote Dr Suzanne Moore Shepherd in an article published in eMedicine earlier this year. Moore is Associate Professor, Department of Emergency Medicine, at the Hospital of the University of Pennsylvania and Director of Education and Research, PENN Travel Medicine.

According to Moore, drowning is defined as:

“death secondary to asphyxia while immersed in a liquid, usually water, or within 24 hours of submersion”.

The phrase “within 24 hours of submersion” includes what has been more commonly termed “dry drowning”, where the victim gets water in the lungs but does not drown straight away, like Johnny, they could walk home and die later.

It is not easy to get hold of statistics on drowning, because there has been confusion about what constitutes drowning, and bringing research together under one term.

At the 2002 World Congress on Drowning, held in Amsterdam, a group of experts suggested a new consensus definition for drowning in order to reduce the confusion over the large number of terms and definitions, currently exceeding 20, that have appeared in the literature. This would remove the terms “wet drowning, dry drowning, active or passive drowning, near-drowning, secondary drowning, and silent drowning” from the literature, said Moore.

Having a universal single definition would help to make the study and analysis of drowning in its various forms more effective, which would lead to better surveillance and prevention.

Unfortunately for Cassandra Jackson, this was not the case, and she probably wishes she had known earlier what she has learned since her son’s tragic death. She said Johnny “was very loving, full of life”, he was “my little man”, she said.