Doctors are being put on alert over a severe strain of hand, foot and mouth disease after some children were admitted to hospital.
The childhood illness, which commonly infects babies and preschoolers, has also spread to some adults, which health officials say is unusual.
Dozens of children have been treated at Auckland's Starship Hospital for dehydration caused by the disease.
Auckland District Health Board director of child health Dr Richard Aickin said two to three cases a day were being seen at the children's emergency department.
"That's only a small proportion of those children who are acquiring the disease because you have to have it as a more severe problem if you are going to come into a hospital emergency department, so there'll be quite a lot that GPs are seeing and more where the families are not going to the doctor."
He said this outbreak was more severe and a result of a less common strain of the coxsackie virus, CVA6, which infected adults more easily.
"What we usually expect is children get hand, foot and mouth once and then they become immune and we don't see it in older children or adults. The A6 is much less common and that's why adults are now getting it."
Waikato District Health Board medical officer of health Dr Anita Bell said a bulletin outlining the outbreak was being sent to Hamilton GPs.
It followed an increase in calls from preschools and a similar warning from the Auckland Regional Public Health Service to health boards and primary health organisations across Auckland last week.
In a report to the Ministry of Health, Starship paediatric infectious disease consultant Dr Emma Best said the less common strain was causing infections in Auckland and other North Island areas.
The disease was not notifiable and did not have a vaccination because there were too many strains.
The severe cases may present with a more extensive rash including on the arms, legs, bottom, and groin, as well as hands, feet and around the mouth.
City Limits Childcare Company in Hamilton said seven babies came down with the illness within days of each other in the last last week.
FEVER, RASH FIRST SIGNS OF TROUBLE
When toddler Kellim Oliver developed a high temperature and what looked like a dribble rash on his chin, mum Alicia put it down to teething.
But when the 20-month-old Hamilton boy was so unwell the next night he couldn't sleep, she rang Healthline at 1am to try to get answers.
"I wanted to find out what I could do for him. We probably got about two hours sleep."
By then Kellim's rash had developed into little red "pimples" covering his hands and mouth.
The next day, the third day of the fever, Mrs Oliver took her eldest son to the doctor, who diagnosed hand, foot and mouth disease.
"He was really upset. He had a rash over his whole body. On his hands, feet and mouth it was more intense and he had blisters."
All the 26-year-old could do was give her son Pamol to reduce the fever and pain.
The symptoms lasted about a week.
Fortunately, Kellim's 5-month-old brother, Aiden, didn't catch the contagious disease.
Another mum, Yvette Ronaldson, said her 7-month-old son, Harry, caught hand, foot and mouth last week.
"It's pretty nasty. His bum was raw, it had welts all over it."
Watch out for the signs of hand, foot and mouth
When my 3-year-old son lay down on the floor of a shop I knew he was a little more than tired.
By the time I got him home his cheeks were flush and he was running a temperature.
At dinner his appetite was depleted and that night I was up and down like a "yo-yo" with a little boy who only wants his mum when he's sick.
We administered Pamol, but it did little to dull the effects of the fever, his head by now boiling hot.
The next day he appeared a lot better, and after much insistence from him and against my better judgement, he went off to preschool for a couple of hours in the afternoon.
But that night the fever returned, the crying continued and I succumbed to squeezing in beside him, too tired to kneel any longer at his bedside holding his hand.
The next morning he again appeared better.
He had three very tiny red "pimples" on one check and a blister in the corner of his mouth. I was horrified that it might be a cold sore.
Again he went off to preschool and we off to work, but at 3pm when his aunt a nurse picked him up she drove him straight to our house.
"I think he's got hand, foot and mouth," she said. "It's going around."
That night the spots began to show around his mouth and chin, on his fingers and hands, toes, soles of his feet, in the creases of his legs and elbows, and around his buttocks and groin.
After another sleepless night and lots of Pamol, I took the day off work and we dragged ourselves to the doctor.
She confirmed the disease and gave us more Pamol. He had to stay away from preschool until the spots disappeared.
I had been vigilant about handwashing to prevent the spread but soon after we arrived home I began to feel unwell.
My body ached, my head throbbed, my throat stung and I felt like I might topple over if I stood up too fast.
My energy was gone and to make matters worse I had an unhappy child to care for. It was not a good day.
The next day was much the same, but after some paracetamol I felt a bit better and thanks to my parents I had an afternoon of rest on the couch.
Then, that night, as quickly as the malaise descended, it lifted.
Two days later though, the spots appeared. And they were painful.
They were all over my hands and feet. It hurt to wear shoes and every time I used my hands to do anything that required the faintest of pressure on my fingers it stung.
By the fifth day I felt a lot better, the pain in the hands and feet subsided but the spots were still visible. It wasn't a pretty sight.
Finally, after seven days, and with the spots slowly beginning to recede, I returned to work.
Fortunately my husband and a house guest did not catch the disease and neither did any colleagues, or any other children at the preschool.
Now, almost two weeks later, the spots have turned into calluses and are beginning to flake off.
And as for the boy, he's almost flake free, there's no spotty scars and he's back to sleeping through the night without mummy.
HAND, FOOT AND MOUTH
* Symptoms include mild fever, red blisters on the tongue, mouth, hands and feet, sore throat and mouth and loss of appetite.
* Contagious for seven to 10 days.
* Spread by coughing, sneezing, contact with mucus, saliva or faeces of an infected person.
* Symptoms often confused with chickenpox.
Source: Ministry of Health