When is COVID-19 most contagious? How long after an exposure does it take to test positive?

IMAGE: Many of us used the long weekend to catch up with loved ones, but what’s the COVID-19 risk? (Pexels: Askar Abayev)

Source: ABCnews

If you spent the Easter long weekend catching up with friends and family, you might have been exposed to COVID-19 and not know it. 

Here’s a rough guide that will help you work out what your risk of infection is. 

When are people most contagious?

Generally, people are most contagious in the early stages of their infection

That’s roughly about one or two days before you start developing symptoms, and then another one or two days after that, according to Harvard Medical School. 

But it’s important to remember that one person’s infectious period can differ from another’s. 

And infected people can pass on the virus whether they develop symptoms or not. 

How long after exposure will symptoms start to show?

Probably three days — so, if you contracted the virus from someone you spent time with on Good Friday, your symptoms might have developed yesterday.

That’s because research suggests the incubation period for the Omicron variant is shorter than earlier strains.

Harvard Medical School said it looked like Omicron symptoms start appearing three days after exposure, while it was four days for Delta and five days for earlier strains. 

However, some people who contract the virus will never develop symptoms.

What symptoms should I look out for?

We’re well-versed in the standard COVID-19 symptoms: cough, fever, loss of smell, headaches, fatigue and a runny nose

But gastro-like symptoms seem to be on the rise among COVID-19 patients lately, with reports of diarrhoea, vomiting and loss of appetite becoming common complaints. 

Other research suggests a hoarse voice is more common in Omicron cases than Delta strains. 

How long does it take to test positive after exposure?

It depends on which test you take. 

Preliminary research on the Omicron outbreak suggests rapid antigen tests (RATs) may not detect COVID-19 until at least two days after someone is exposed to the virus, and the Therapeutic Goods Administration (TGA) says they’re not as accurate if you do not have symptoms.

So it’s likely you won’t test positive on a RAT until a few days after exposure, but you could still get a false negative result on a RAT even after a few days.

On the other hand, PCR tests are likely to detect the virus earlier than RATs.

The TGA says those tests — the ones you have to go to a testing clinic for — can sometimes detect the virus even before people start noticing symptoms.

Peter Richmond, a vaccine and paediatrics expert at the University of Western Australia, said PCR tests could pick up very low levels of the virus and could return a positive result “potentially even before you’re infectious”.

So when should I get tested?

When you develop symptoms. 

Professor Richmond says you shouldn’t rush out to get tested the day after you think you could have been exposed to the virus. It’s unlikely the virus will be picked up that early.

“You want to wait two to three days before you get your PCR test,” he said. 

The same goes for RATS. 

Registered nurse and disease control expert Thea van de Mortel from Griffith University recommended waiting a couple of days after being exposed to the virus before taking a rapid test — that’s because RATs usually don’t pick up the virus unless someone has symptoms.

“It takes a while for the viral load to get up to the point where it’s detectable,” Professor van de Mortel said. 

Does that mean I should get re-tested?

If you’ve returned a negative result on a RAT but you still have symptoms, the advice is to isolate for another 24 hours before doing another RAT or have a PCR test.

That’s because RATs work by detecting a protein the virus produces, and giving yourself another day may give the virus more time to produce a detectable amount of that protein.

“In that interval, if you do have COVID, you will have increased the amount of virus you have and, therefore, increased the amount of protein and will then get a positive RAT,” Professor Richmond said.

“But if you’ve got a negative PCR with symptoms, you’re probably OK. You don’t need to necessarily repeat it the following day.”

How long are you contagious for after testing positive?

Most people will no longer be contagious after 10 days from the onset of their symptoms.