Researchers have found the virus behind Covid-19 can survive for up to 28 days on smooth surfaces like banknotes, steel and phone screens.
Despite the findings, just published by Australian scientists, a Kiwi epidemiologist says New Zealand's biggest risk for Covid-19 spread remains droplets hanging in the air after being breathed or sneezed.
The research, undertaken at the CSIRO's Australian Centre for Disease Preparedness, found that SARS-CoV-2 survived longer at lower temperatures and tended to survive longer on non-porous or smooth surfaces, compared to rougher surfaces like cotton.
They also found it survived longer on paper banknotes than plastic banknotes, like New Zealand's.
"Our results show that SARS-CoV-2 can remain infectious on surfaces for long periods of time, reinforcing the need for good practices such as regular handwashing and cleaning surfaces," ACDP deputy director Dr Debbie Eagles said.
"At 20C, which is about room temperature, we found that the virus was extremely robust, surviving for 28 days on smooth surfaces such as glass found on mobile phone screens and plastic banknotes.
"For context, similar experiments for Influenza A have found that it survived on surfaces for 17 days, which highlights just how resilient SARS-CoV-2 is."
The research involved drying virus in an artificial mucus on different surfaces, at concentrations similar to those reported in samples from infected patients and then re-isolating the virus over a month.
Further experiments were carried out at 30C and 40C, with survival times decreasing as the temperature increased.
The study was also carried out in the dark, to remove the effect of UV light as research has demonstrated direct sunlight can rapidly inactivate the virus.
"While the precise role of surface transmission, the degree of surface contact and the amount of virus required for infection is yet to be determined, establishing how long this virus remains viable on surfaces is critical for developing risk mitigation strategies in high contact areas," Eagles said.
ACDP director Professor Trevor Drew said many viruses remained viable on surfaces outside their host.
"How long they can survive and remain infectious depends on the type of virus, quantity, the surface, environmental conditions and how it's deposited – for example touch vs droplets emitted by coughing," Drew said.
"Proteins and fats in body fluids can also significantly increase virus survival times.
"The research may also help to explain the apparent persistence and spread of SARS-CoV-2 in cool environments with high lipid or protein contamination, such as meat processing facilities and how we might better address that risk."
CSIRO, in partnership with the Australian Department of Defence, undertook the studies in collaboration with the 5 Nation Research and Development Council, which comprises representatives from the UK, US, Canada, New Zealand and Australia.
Each country was conducting research on different aspects of virus survivability with the results shared as they become available.
Otago University epidemiologist Professor Michael Baker said the risk of contaminated surfaces had been highlighted by separate New Zealand cases thought to have been spread from a lift button and a rubbish bin.
The main modes of transmission of the virus were still being debated among scientists, he said surfaces still remained the least threatening.
"The importance of droplets has never been in doubt - and there seems to be growing support for the role of aerosols in some outbreaks," he said.
"But I haven't yet seen any evidence that surfaces have contributed to outbreaks."