When Stephanie Elderton's twin boys caught a cold, she never imagined that one of them would end up in intensive care. But the cold developed into bronchiolitis - and while bronchiolitis is usually a mild illness, in rare cases it becomes serious.

Reece and Luca are adorable twin boys.

Now aged 14 months, they were born prematurely in 2017, arriving at 34 weeks. Reece weighed 4lb 7oz and Luca 4lb 2oz.

"They are identical boys but personality wise they are completely different," says Stephanie. "They are very chatty, they're very lively. They love balls and any pop up toys and spinning toys. They like to laugh and they like to run.

"Well - Reece likes to run. Luca's a lot more serious, I would say, than Reece. He is quite happy to just be by himself and play by himself."

Despite being premature, the twins did not require any special care. Soon after the birth they went home to join their older brother Jamie, who is now five.

But in January 2018, when the twins were five-and-a-half weeks old, Stephanie noticed that a cold they had both been suffering from was getting worse, so she asked her GP's surgery for advice.

"Luca stopped feeding as much and I mentioned this to the doctor, I mentioned this to the health visitor and they basically said, 'No, it's absolutely fine, they've just got a cold.'

"I said, 'OK, no problem, we'll just carry on as we are.' Then, when they were six weeks old, he wasn't waking, he wasn't eating, and so I took him back to the doctor's and I was like, 'There is something really wrong because this is just not how a baby should be.'"

Stephanie also noticed changes in the way the twins were breathing - it was much faster than normal and more laboured.

The GP sent Stephanie straight to the local hospital, Hinchingbrooke in Cambridgeshire, where Luca was instantly put on a monitor to check the oxygen levels in his blood.

"They said he really wasn't very well and they put him straight into the high dependency unit (HDU) and then they looked at Reece and went, 'We think he's the same,'" says Stephanie.

The HDU is a ward designed for people who need close observation, but not intensive care.

The hospital doctors told Stephanie the twins were suffering from bronchiolitis, a condition she had never heard of.

"Bronchiolitis is a viral chest infection and it's usually caused by the common viruses that cause colds in adults," says Dr Francis Gilchrist, a consultant in paediatric respiratory medicine and trustee of the British Lung Foundation.

It affects children under one year old, starting off with familiar cold symptoms. But with bronchiolitis the airways in the child's lungs become inflamed and swollen, causing them to narrow. In severe cases smaller tubes in the child's lungs - the bronchioles - clog up with mucus.

In the vast majority of cases, children recover at home within two to three weeks. But just occasionally severe cases occur - about 2-3% of all infants require hospitalisation, according to Francis Gilchrist.

The frustrating thing about bronchiolitis, he says, is that there is no effective treatment for the underlying condition.

"All the care that we do is supportive. So if necessary we give oxygen or support their breathing, or if they're really unwell they go on to have artificial ventilation in intensive care." Fortunately this is very rare - it only applies to 0.1%, or one in 1,000 children.

In the HDU, Luca was kept on observation for 24 hours but showed no signs of improvement.

"They did some X-rays to see what was going on and basically the whole of his left lung was completely blocked," says Stephanie.

At this point, the decision was taken to move him to Addenbrooke's hospital in Cambridge, where he could be ventilated. But then things suddenly got serious.

"When they tried to tube him, he basically stopped breathing altogether," says Stephanie. "They had to give him CPR quite a few times and then they transferred us straight to Addenbrooke's hospital, to intensive care."

There the ventilator did the breathing for Luca to ensure more oxygen reached his tiny lungs. It was very hard for Stephanie to watch.

"He's just lying there, he's not awake because he's sedated and you can touch him, you can talk to him but he's not really him, you can't cuddle him or anything," she says.

To make things harder, Reece had remained in Hinchingbrooke hospital and she had to keep phoning the ward for updates.

"It was very tough and I didn't have my car either so I couldn't come back and forth so I just stayed at Addenbrooke's," says Stephanie. "I had to kind of shut Reece out - 'Luca's the one that needs me now - Reece is fine, he's getting the help he needs' - and just kind of not think about it. Because otherwise that would have worn me down even more."

Fortunately, Stephanie's mother was able to spend time at Reece's bedside.

Because the boys were twins the medical team suspected they would both end up in the intensive care unit at Addenbrooke's, Stephanie says. But although Reece was very poorly, being fed via a nasal gastric tube, he stayed at Hinchingbrooke.

Most cases of bronchiolitis are caused by Respiratory Syncytial Virus (RSV), something that most children will have been exposed to by the time they are three. However it can also be caused by other viruses, such as rhinovirus, the most common cause of the common cold.

Why some children are affected more seriously than others, is still not fully understood, says Francis Gilchrist.

"There are certain risk factors that children have that mean they're more at risk of having severe bronchiolitis and that would be if they're very young, if they were born prematurely, if they have pre-existing disease, such as congenital heart disease, or if they have an underlying problem with their immune system.

"But there are some children who have none of those risk factors and end up with a severe episode, and we can't fully explain why."

After five days in intensive care, the medical team tried to take Luca off the ventilator and transfer him to a different method of breathing support, known as Continuous Positive Air Pressure (CPAP), but Stephanie says Luca couldn't take it and had to be put back on the ventilator again.

"I was very disheartened by that, because after five days he hadn't got any better, we're kind of moving backwards not forwards," says Stephanie. "It felt as if it was never going to end."

During this time, Luca was having chest physiotherapy to try and loosen the mucus from his airways.

Finally, after seven days, he was taken off the ventilator and began to improve. Stephanie says it felt very strange to cuddle him again for the first time.

"It was a bit like, 'Aww I don't remember how to do this,'" she says.

Luca was taken back to the children's ward at Hinchingbrooke. His twin, Reece, had been discharged the day before, but Luca had a visit from his older brother, Jamie, who had been staying with Stephanie's parents while the twins were in hospital.

"It was just amazing to see him, because it felt like I hadn't seen him for such a long time," says Stephanie.

Twenty-four hours later Luca was discharged too and the family was finally reunited at home.

Terrified the boys would catch another cold, Stephanie did not take them outside. But two weeks later she noticed they were breathing rapidly again - and this time they had spots. She called an ambulance and the twins ended up back at Hinchingbrooke.

There they were diagnosed with meningitis and put on intravenous antibiotics.

There is no association between bronchiolitis and bacterial meningitis, says Francis Gilchrist. It seems as though the boys were just unlucky.

After another six days in hospital they were able to return home, but again Stephanie was afraid to take them out.

"Because they're twins, obviously twins seem to be quite unusual, everyone wants to look at them, everyone wants to touch them, all the old ladies want to kiss them. It's just madness. So I was like, 'Please don't touch them, they could get poorly.'"

A year later, she still worries about them getting colds.

"If my bigger one gets ill, I'm like, 'Don't touch them, wash your hands!'" she says. "I'm very frightened every time they cough or anything."

If they do get a cold, they tend to get very wheezy, Stephanie says, but they now have asthma inhalers and other medication to reduce airway inflammation.

She's noticed that many parents know as little about bronchiolitis as she did before her children became ill, and is keen to raise awareness about the illness - and in particular about the possibility of severe symptoms, even if they only occur in a small minority of cases.

"I don't know why it's not out there, because of how serious it can be," she says.

She says her hopes for the future are for her children to stay out of hospital and keep smiling.

But she knows the trauma of winter 2018 didn't just leave her when the children were discharged. "It's going to be here forever," she says.