The Health Ministry is worried about a rising number of meningococcal disease cases. (Video produced in November 2018).

Northland DHB was aware of a "very scary strain" of meningitis six months before it warned the public, an internal memo shows.

On Tuesday, Northland DHB put out a media release warning the public to be vigilant about a "significant increase" of Group W meningococcal disease in the region.

But in May, clinical microbiologist David Hammer had circulated a letter to DHB staff warning of potential cases.

SUPPLIED Dion Hodder, 16, died from meningococcal disease in October.

In the memo, Hammer said "we have not previously had group W strains in Northland but we have had two unrelated cases within one week this year. Sequence typing is awaited but I anticipate that the result will be ST-11".

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The memo said there had been a "significant rise" in meningococcus W ST-11 cases across New Zealand.

"As meningococcal disease peaks in the winter, I suspect that we will be seeing a whole lot more cases soon."

Already this year, 24 cases have been confirmed and six patients have died. Three of those were in Northland.

Hammer's memo noted that doctor-patient conduct carried a very low risk of infection, but said the disease tended to "spread rapidly though areas where younger people congregate, such as schools, hostels, army barracks and university campuses".

He went on to encourage his colleagues to have their children who were older than nine months vaccinated with one of the newer meningococcal vaccines, "to reduce their chances of acquiring an infection from this very scary strain of meningococcus".

On October 20, Northland teenager Dion Hodder was at a St John Youth training camp on Motutapu Island when he fell ill with meningococcal disease.

DANICA MACLEAN/STUFF Northland DHB circulated an internal memo warning of a "very scary" strain of meningococcal disease at least six months before issuing a press release to the public. (file)

The 16-year-old was airlifted to Auckland City Hospital where he received urgent medical treatment but died just before midnight.

His mother Todd Horton and stepfather Lance Horton said Dion had died from the W strain.

The pair had not been made aware of the internal memo or the rise in cases.

Dion's mother said "it's hard to know how to feel about that, really".

"It doesn't really make a lot of difference to us at this point," Horton said.

"Meningococcal is one of those diseases that has been around for a long time and everyone knows the signs and symptoms but I think we just need to be made aware that with these newer strains, some of these signs and symptoms aren't as visible and aren't as prominent."

"I would hate to think of other parents going through what we're going through right now."

Dion's stepfather said he had recently received a phone call from a public nurse who had vaccinated his family, and was told the vaccination "really needed" to be available for "at-risk people" – something they agreed with.

The most at-risk were toddlers and adolescents between the ages of 15 and 19, he said.

"That vaccine should be made to all of those [people]," Horton said.

When asked if DHBs should do more to raise awareness about the strain, Horton said "hell yeah".

"It doesn't present the same as the other strains – it doesn't present at all like meningococcal until it's too late.

"Once you actually get the symptoms, it's too late."

Northland DHB has been approached for comment.