NSW Health has reported a rise in cases of a lesser-known respiratory virus.
Since the early 2000s, human Metapneumovirus has been on the medical radar, with NSW authorities saying that the number of weekly infections has risen from 648 at the beginning of the month to 1,168 in the week ending September 17.
HMPV is usually more common in late winter and spring, according to NSW Health.
What are symptoms of a disease?
The symptoms of the cold aren't that different to that of a common cold, said John-Sebastian Eden, senior researcher and virologist at the University of Sydney.
Its symptoms are very similar to that of COVID-19, the flu and respiratory syncytial virus, which is genetically similar to HMPV.
'' t be a differentiator from COVID or flu... or just really having a cold or having a bad cough... or just really having a cold..... or just really having a cold,'' he said.
Dr Eden said people were unlikely to know about the virus until they tested positive for the virus.
Testing for the virus is performed via a PCR test, however not all PCRs will test specifically for HMPV.
•• Don't visit people who are at high risk of severe illness if you have cold or flu symptoms.
The medical community had a clear consensus that masks are effective for slowing the spread of respiratory illness, but a mix of responses were needed, said Professor William Rawlinson, professor of medicine at the University of New South Wales.
Dr Eden said there are no anti-viral drugs used to treat HMPV, nor is there a vaccine.
Sickers, older and younger people are most at risk.
While HMPV is usually a mild cold for most people, the virus can occasionally escalate and become more serious with young children, older adults and those with compromised immune systems most susceptible, according to NSW Health.
Dr. Eden said children who are below five years of age are at a risk of complication.
It can cause severe health problems if the elderly contract it, he said.
We have had noted outbreaks in previous years at nursing homes... so it can really cover the whole spectrum, he said.
Professor Rawlinson said viruses like HMPV can develop into other respiratory illnesses like pneumonia, but it is very unlikely.
Health officials in New York said there's an underestimation of the number of cases in the community because of the test samples that come back.
Why are there so many cases?
While HMPV tends to be more common towards the end of winter into spring, Sydney Chief Health Officer Kerry Chant said the vigilance during the peak of COVID pandemic meant people took measures that slowed the transmission of many viruses.
The outbreak of respiratory viruses has resurgence. We basically have very little circulation of respiratory viruses because of all those COVID social distancing measures, Chant said.
Dr. Rawlinson said researchers are not sure why the virus is more common at this time of year.
It's probably that people are coming out and mixing more, it's probably spread rather than the virus itself, he said.
It's one of the things we need to research.