"We have a simple message to all countries - test, test, test," Tedros Adhanom Ghebreyesus said last month in a press briefing on measures to fight the coronavirus pandemic in the Swiss city of Geneva.

And health experts worldwide have backed the World Health Health Organization (WHO) director general, saying the best way to fight the pandemic is to "flatten the transmission curve" in order to prevent a sharp spike in cases as seen in Italy and Spain.

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Tedros and other experts agree that mass testing for COVID-19, the disease caused by the coronavirus, would allow positive cases to be isolated and help identify those who came in contact with them, helping to curb further transmission.

But how does testing happen and how does it help? Here is what you need to know about coronavirus testing:

What coronavirus tests are available?

NAAT tests

The most commonly used coronavirus tests are the WHO-recommended Nucleic Acid Amplification Tests (NAAT), which detect the SARS-CoV-2 virus responsible for the COVID-19 disease.

The specimen is usually collected from the upper respiratory tract using the nasopharyngeal swab technique - in which a sample is gathered from the throat behind the nose, containing a mixture of mucous and saliva.

The RT-PCR testing process can take up to 3-4 hours [File: Edgard Garrido/Reuters]

Samples are brought to a specialised laboratory and tested for SARS-CoV-2 using a real-time reverse-transcription polymerase chain reaction (rRT-PCR) assay - a method used to detect the presence of "specific genetic material from a pathogen".

"From reputable laboratories, they [NAAT] are very reliable," Anna Wald, head of Allergy and Infectious Diseases Division at University of Washington, told Al Jazeera.

Wald said that while the technique was good and did not warrant any improvements, it was "just not available enough".

The testing process can take up to 3-4 hours, with results available to patients within several days in most countries.

Serological tests

A serological test is used to detect antibodies present in blood serum. Antibodies are proteins produced by white blood cells to fight foreign bodies such as antigens.

According to Johns Hopkins University, "the serum includes antibodies to specific components of pathogens, called antigens ... recognised by the immune system as foreign and are targeted by the immune response".

According to authors of a recent pre-print, but yet to be peer-reviewed study, serological tests can help detect the rate of infection in a community, and hence determine the rate of mortality from the disease.

The study also asserts the test can help identify individuals who have developed antibodies to the SARS-CoV-2 virus, allowing them to serve as donors to those currently infected with COVID-19.

Scientist Linqi Zhang in his laboratory where he researches COVID-19 antibodies for possible use in a drug at Tsinghua University's Research Center for Public Health in Beijing [File: Thomas Peter /Reuters]

For some, it is too early to tell exactly how effective serology tests will be in tackling COVID-19.

"It is not clear if they will be a game-changer at this time," Waleed Javaid, director of Infection Prevention and Control at Mount Sinai in New York, told Al Jazeera.

"Serology tests tell you about possible infection or exposure in the past, but not if you are currently infectious," he said.

Currently, serology tests are in developing stages for both commercial and non-commercial use, and only a handful of countries like China and Singapore use it for coronavirus testing.

On April 2, the US Food and Drug Administration approved the first serological test produced by biotechnology company Cellex, that tests for coronavirus antibodies in blood obtained from pricking a finger. The test can reveal if a person has COVID-19 in approximately 15 minutes, the company claims.

Who will get tested?

Testing for coronavirus in most parts of the world is largely prioritised for those above 65 and severely ill patients.

Many people who show mild symptoms are unlikely to get tested in countries such as the United States, often due to lack of testing kits.

The WHO has recommended that if a person tests positive, it is important to figure out those they came into "close contact with up to two days before they developed symptoms and test those people too", but only those who show symptoms.

Where can you get tested?

In most countries, coronavirus tests take place largely in specialised labs and medical facilities like hospitals and clinics.

However, in recent weeks, some countries like Germany, Canada, the United Arab Emirates and South Korea have opened up testing centres outside of traditional hospital settings.

In South Korea, many cities have started authorising road-side tests, touted to cut testing time to about a third, while also lowering the risk of catching the virus - since the individual is in his vehicle. The entire process is believed to take approximately 10 minutes.

"A drive-through sampling site is developed to overcome bottleneck in sampling process," Lee Hyukmin of the Yonsei University College of Medicine in Seoul, told Al Jazeera.

Medical staff wearing protective suites work to take samples from drivers with suspected symptoms of the coronavirus at a "drive-through" virus test facility in Goyang, South Korea [Ahn Young-joon/AP]

"It is a good solution for rapid sampling. In Korea, the sampling process is very time-consuming because of bio-safety issues to protect healthcare personnel. So, enough tests cannot be done even with early expansion of lab capacity," Hyukmin added.

Several companies in the US claim to have created home-based coronavirus kits.

However, the US Food and Drug Administration has strongly asserted that it has not "authorised any test that is available to purchase for testing yourself at home for COVID-19".

In Bangladesh, researchers have produced a testing kit which they say can detect SaRs-CoV-2 antibodies in 15 minutes. The kits, which have been approved by the Bangladeshi government for production, cost a mere $3 each.

Researchers in Senegal announced in late March a new home-based coronavirus test that costs approximately $1 - and can detect an active infection using a saliva swab, or a previously undetected case using an at-home finger-prick blood test to that identifies antibodies to the virus.

Infectious diseases specialist at the University Health Network in Toronto Abdu Sharkawy believes home-based kits would allow a significant expansion of testing. But he added that home tests are more likely to be "less sensitive than lab-based tests".

Is mass testing feasible?

Germany and South Korea have been widely praised for their efforts to aggressively test for coronavirus on a mass scale, with the former claiming it has the capacity to conduct 500,000 tests a week.

However, for many countries, especially middle/low-income nations, testing on a large scale may not be feasible.

"I think the unique challenges in low and middle-income countries, many of which are recognised as having high burdens of (other) diseases, may be more related to the lack of financial safety net," Maia Lesosky of Cape Town University in South Africa, told Al Jazeera.

Elaborating further, Lesosky said the choice to implement mass testing for a new disease could very well take away the "capacity to diagnose or treat existing diseases".

In the context of her own country, South Africa, one the worst affected countries in Africa, Lesosky said it was a large country and not all areas are easily accessible, which "translates directly into logistical challenges in reaching remote communities to provide testing".

"Anything was possible with enough funding", she said, however, in the absence of it, the "benefits of mass testing need to be weighed carefully against potential drawbacks".

Moreover, Lesosky stressed: "mass testing ... can be beneficial only if it is closely tied to public health programmes to limit further spread", such as separate testing and treatment facilities and restriction of public gathering.

"This may be of greater challenge where healthcare systems are less robust," she added.