The third case reported is a woman in her 30s who is the daughter of a 53-year-old woman who worked as a maid at the same MIQ.
The maid had contracted the virus from a male soldier who authorities now believe had contracted Covid-19 while handling the baggage of two Fijian nationals who returned from India on April 10.
The mother-daughter pair were involved last Friday and Saturday with funeral rites which took them between Nadi and the Lautoka suburb of Tavakubu, and which exposed at least 500 people to Covid-19.
Calling the funeral a "potential superspreader event", Fiji's Health Permanent Secretary Dr James Fong said: "Together, these two patients represent the highest-risk cases Fiji has ever contended with.
"Now that we know both the mother and daughter are Covid-positive, the risk that there was of transmission of the virus to the mother's fellow passengers during her travel from the Tavakubu funeral to Nadi on Saturday is high."
"We know there were at least 500 people present at the funeral. The mother was there for a few hours, which is more than long enough to transmit the virus to others. We have directed all those present at the funeral to stay at home for the next two weeks while they await screening from the Ministry of Health and Medical Services."
While the two women have become the central focus of the Ministry of Health's contact tracing activities which have spread across the entire main island of Viti Levu, a lot of the Government's success hinges on its ability to locate drivers of vehicles the women and their relatives travelled in.
While health authorities have located some mourners, it has been difficult to find the drivers of three mini buses and a grey taxi who transported the women and other relatives back and forth between the two cities between April 16 and 17.
"We have yet to confirm it via tests, but we are certain there are more cases out there," Fong said. "So, we are mobilising a massive house-to-house screening effort in the Nadi and Lautoka containment area to determine people's travel history, so we know where they have been, and screen for Covid-like symptoms, so we know if they are sick.
"We will be testing immediately and often. We have the capacity to run 600 Covid tests per day. That is how many tests we plan to run every day for the next two weeks, at least."
Questions over contact tracing app
Meanwhile, the heath ministry is continuing to urge people to download its careFIJI app to aid in its contact tracing, but it was not clear if authorities have been able to download data from the app.
Customised from the Singaporean Government's contact tracing technology, the app was introduced last year but had been met with public scepticism.
"I cannot stress enough how important it is that you enforce physical distancing within your businesses and require that customers have the careFIJI app turned on while they are on your premises," Fong said.
"CareFIJI is one of the most efficient contact tracing tools we have. If you have careFIJI, and you come into contact with someone who has the virus, we can alert you quickly to keep you and your family safe. The more Fijians have this app downloaded, the more quickly we can flush out the virus and return life to normal."
Fong was not able to confirm whether any data had been extracted from the app to aid in current contact tracing but said this was a situation when it would have provided critical support.