An epidemiologist is warning New Zealand needs to start preparing now for an expected influx of winter illnesses, based on what the northern hemisphere is going through right now.

Professor Amanda Kvalsvig, of the University of Otago's Department of Public Health, said disease patterns observed overseas were likely to be replicated here in six months' time.

The northern hemisphere winter has seen a wave of group A strep infections, or 'strep throat'. Sometimes, particularly in children, it can cause scarlet fever.

Since mid-September, England has reported almost 34,000 cases of scarlet fever - seven times more than at the same point in what the UK Health Security Agency dubbed the "last comparably high season" of 2017/18, and more than all of 2017 and 2018 put together.

All-up, this wave of group A strep has killed 122 people so far, including 25 children, in England.

Kvalsvig said the bacteria was a particular concern because it was also the cause of rheumatic fever, which New Zealand had very high rates of. It's a serious autoimmune disease that can develop if strep throat or other group A strep infections - such as in the skin - aren't treated promptly. Rare in much of the developed world, researchers here have linked its ongoing presence in Aotearoa to poverty and poor housing.

The surge comes on top of a growing number of Covid-19 infections in England and Scotland, outbreaks of respiratory syncytial virus (RSV) across the UK, Europe and US and rising flu cases - a combination media dubbed the 'tripledemic'.

"Some countries are experiencing RSV outbreaks much earlier than they normally do," said Kavlsvig.

"They're experiencing higher rates of hospitalisations and more severe illness. We're seeing infections that aren't usually very widespread becoming widespread. Group A streptococcus is an example in the UK."

Kavlsvig said New Zealand also needs to look at how infectious diseases interact and how one can make people more susceptible to others.

She is working on a five-year research programme into breaking the cycle of 'syndemics', where multiple diseases or inequalities exacerbate the spread of illness and their severity. High-profile epidemiologist Michael Baker is also involved.

She said Covid-19 had shown schools can be superspreaders, and it needed to change.

"It's absolutely vital that we have that good situation awareness, so that when an outbreak happens we can move in early to prevent and control it. At the moment, our child data system is very patchy, so there's work to do there."

Kvalsvig said consistent, detailed data and high ventilation standards in schools would be a great place to start. The programme is due to conclude in 2025.

-RNZ