It is the single largest cluster of positive cases detected on the Mediterranean island since the first case was reported on March 7. The Maltese Health Ministry said 85 of 94 rescued migrants had been tested so far. It gave no further information about their condition.
The discovery that so many of the group had COVID-19 has bolsterered concerns that a recent increase in new arrivals could undermine local efforts to eliminate the disease.
It has also sparked fresh worries over the safety of the migrants who are already putting their lives at risk on dangerous journeys across the Mediterranean.
The nationalities of the migrants has not been revealed but their dinghy is believed to have set sail from Libya.
A health ministry spokesman said: “So far, the swab results of 85 of these migrants are available and 65 of these 85 migrants have tested positive.
“Migrants arriving by boat are immediately quarantined for 14 days and tested.
“The migrants who are positive will continue to be isolated and the rest will remain in quarantine and followed up.”
The spokesman tried to play down fears the migrants’ arrival could cause a fresh spike in cases on the island.
He said: “This group arrived in Malta together and were in contact with very few other people before they were tested.”
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Malta’s armed forces rescued the migrants north of Libya on Sunday and took them ashore at a military base near the capital Valletta.
A volunteer organisation, Alarm Phone, on Sunday morning said the dinghy was overcrowded and taking in water.
It said the boat was located within Malta’s search-and-rescue region.
The migrants had issued a distress signal from their packed dinghy on Sunday but it took more than 30 hours for rescuers to reach them.
Non-governmental agencies have accused both Malta and Italy of deliberately slowing down rescue missions in an effort to dissuade people from putting to sea and seeking a better life in Europe.
Prime Minister Robert Abela has insisted the government will be doing everything it can to tackle the immigration crisis faced by the country.
Mr Abela said he understood the difficulties faced by those living in areas most affected by immigration.
He said: “We understand the sentiment felt, and we are doing our utmost to finding a solution to this problem.
“We are going to other countries and we are insisting with them that this is not a Maltese problem, but a European one.”