Why you could test negative despite having coronavirus

False-negative testing results for coronavirus is leading to some patients being tested seven times before finally being diagnosed with the illness.

On Friday New Zealand's first case of coronavirus was confirmed to be an individual in their 60s who had just arrived back in the country after spending time in Iran and a stopover in Bali.

When they started displaying the symptoms of coronavirus they were tested, but the first two tests came back negative.

The Ministry of Health said it wasn't until a more "specific" third test was completed that the case of coronavirus was confirmed.

"This person also tested negative for COVID-19 on two occasions but obviously the clinical judgement was to continue and look in greater detail," a spokesperson for the ministry said.

BBC News reported some patients in China were receiving up to six negative results before finally being diagnosed when the seventh test came back positive.

There are a few possible reasons why initial testing isn't conclusive in confirming whether or not a patient has the virus.

BBC says suspected cases are tested using an oral swab which results might change depending on how thoroughly it is done.

False-negative results may occur if the testing swabs are stored in a temperature where the virus deteriorates before it is checked.

Another reason tests may come back incorrect is the virus may be "hiding" somewhere else in the patient's body and isn't picked up on the swab.

Marc Lipsitch, an epidemiologist at the Harvard T.H. Chan School of Public Health told the New York Times: "A negative test is not a definitive that there is no more virus in that person".

He compared the situation to a jam jar. It may have mould on top which can be scraped off to give the impression it is all gone, but there may still be mould further down the jar.

BBC News says because of the uncertainty around some results, officials in Hubei province in China have been counting the cases of the illness based on symptoms while they wait for patients to be double and triple checked for coronavirus.

Similar cases have been reported in Thailand and Singapore, the news site reported.

The Ministry of Health has been approached for comment but responded that they are inundated with enquiries at the moment.