New wave: Covid-19 in wastewater at highest level in 18 months

Monday, 27 May 2024

Wastewater data is backing up what we've been seeing - Covid levels are back up.

The amount of Covid-19 in wastewater is the highest it has been in 18 months, as experts signal we’re experiencing another wave of the virus.

National surveillance data for the week ending May 19 showed the level of SARS-CoV-2 detected in wastewater was more than double the previous week, and was at the highest level reported since December 2022.

It comes as reported cases and Covid-19 hospitalisations have also risen week-on-week, and GPs are reporting “seeing a lot” of the virus on the frontline.

What are the experts saying?

Epidemiologist and University of Otago Professor Michael Baker said recent wastewater data showed the highest levels of virus in almost 18 months.

“This current peak is higher than anything we saw last year.”

Baker said it’s hard to know how big or how sustained this wave will be.

Hospital admissions with Covid-19 had increased ‘rapidly’ in recent weeks, a leading Covid-19 modeller says, as wastewater levels reach a height not seen in 18 months.

“But I think it is a huge lesson that this virus is still very much with us and we need to be taking precautions against it.”

Dr Joanne Hewitt, science leader, health and environment at the Institute of Environmental Science and Research (ESR), said the last time wastewater levels were this high was December 2022.

Wastewater detections have been “quite elevated” over the last three weeks, with increases seen at most surveillance sites across the motu, she said.

Hewitt said these elevated levels likely indicate more infections and more cases in the community.

Anecdotally, “lots of people… seem to have Covid-19 at the moment, [there] seems to be a lot more around”, Hewitt said.

Tauranga-based GP, and medical director for the College of GPs, Dr Luke Bradford said Covid-19 is “definitely going up”.

Dr Luke Bradford, medical director of the Royal NZ College of GPs, and a GP based in Tauranga, says they’re definitely seeing an increase in Covid-19 at the moment.

“We’re seeing a lot… [we] all have staff and colleagues off-work with it, and [are] providing work certificates and general advice.”

Covid-19 modeller and University of Canterbury Professor Michael Plank said the “significant” increase in reported cases and wastewater detections over recent weeks suggested “we are experiencing another wave of Covid-19 at the moment”.

Plank said there were a number of factors likely contributing to the increase we’re seeing.

For one, it’s been about six months since our last significant wave, so people’s immunity will have waned, he said.

There’s some newer variants which have a bit of a growth advantage, and the timing – at the start of winter, with people heading indoors in colder weather – also gives the virus “a bit of a helping hand” to spread more easily.

Meanwhile, GPs were also seeing more “nasty” flu starting to “bubble up”, though not currently to the level of Covid-19, Bradford said.

So, what does the data tell us is going on?

Health New Zealand data show there were 6636 Covid-19 cases reported in the last seven days, with a daily new case average of 948 ‒ up from 762 the week prior.

There were 282 people in hospital with Covid-19 as of midnight Sunday, up from 242 at the same time last week. No-one was in an intensive care unit with Covid-19.

But it’s not just Covid-19 in the mix.

ESR weekly virology data showed a rise in the number of positive influenza viruses, from 57 in the week ending May 5, to 138 in the week ending May 19 — more than doubling over a fortnight.

To the week ending May 19, there have also been 2079 cases of RSV since January 1, up from 1754 the week prior, ESR reported.

Experts say Aotearoa is likely experiencing another wave of Covid-19, just as flu season is kicking off.

In that last week, Waikato-based labs saw the highest number of RSV cases (by voluntarily reporting laboratories), with 59 cases, followed by 33 in Auckland.

What should we know going forward?

Plank said he wasn’t reading too much into a single weeks’ worth of wastewater data, as it can “spike up and down quite a lot from one week to another”.

He said information in coming weeks would confirm whether this continued to increase, or if the most recent wastewater data was a bit of an anomaly.

In the meantime, as winter beckons and there are different illnesses circulating, Baker said if people get sick they should treat it as Covid-19 unless proven otherwise, including testing and staying home if unwell.

He also encouraged people to ensure they’re up-to-date with their Covid-19 vaccines and to be vaccinated against influenza; and for older, vulnerable, or immune-compromised people to wear high-quality respirator-style masks in crowded places, such as buses.