The single-day count of coronavirus cases in Mumbai has almost tripled in four days, rising from 204 on Monday to 602 on Thursday. The daily count of cases in the city has seen a consistent rise since the beginning of this week. On Tuesday, 327 cases were reported, while on Wednesday, the tally rose to 490.

The positivity rate jumped to 1.5% on Thursday from 0.6% on Monday.

On Thursday, the city also recorded the highest number of cases in a single day since October 10, when 629 infections were reported in Mumbai.

Data from civic body Brihanmumbai Municipal Corporation showed that the suburban parts of Mumbai had more active cases than the island city. There were 2,813 active cases in Mumbai on Thursday.

Mangala Gomare, the executive health officer at the civic body, told Scroll.in that an increase in social gatherings and laxity in use of masks were could be a reason for the surge in cases.

“We have also increased testing from 30,000 samples [in a day] to 40,000-50,000 samples, which has led to more case detection,” Gomare added

The health official, however, said it was unclear if the Omicron variant of Covid-19 was also responsible for the increase in number of cases.

Mumbai is currently focusing its genome sequencing resources on international travellers, people who are getting reinfected, breakthrough infections and those who require longer periods of hospitalisation, or died due to Covid-19. The city still lacks an aggressive sequencing process at the community level.

“We have decided to send all our positive samples of one particular day for sequencing,” Gomare told Scroll.in.

Maharashtra state epidemiologist Pradeep Awate said that so far the rise in number of cases and positivity rate was limited to Mumbai, Pune and to some extent, Thane.

“We are planning to send 300-400 positive samples from Pune for genome sequencing,” Awate said. “This will help assess spread of Omicron in community.”

Maharashtra has sequenced 2,400 samples through community surveillance since November.

Awate said they had collected samples of cases with breakthrough infections, reinfections, severe symptoms, those who required intensive treatment, and samples of those who died due to Covid-19.

“Out of these 2,400, we found nine Omicron cases,” he said. “All of them had either had some travel history or came in contact with a traveller,” Awate said.

In total, Maharashtra has reported 88 Omicron cases so far. The 79 cases other than the nine detected through community surveillance were reported among international travellers.

On Thursday, Mumbai detected five new Omicron cases. Two of the infected persons were fully vaccinated and three had taken the first dose. All five had travelled from abroad and have been sent for isolation at the city’s Seven Hills Hospital.

The five patients include a 27-year-old woman who arrived in Mumbai on December 17 from London, a 21-year-old woman who came from Abu Dhabi on the same day and a 15-year-old girl from Pune who reached the city on December 17 from London.

The two other patients are women, both aged 42, who arrived from Muscat on December 15.

Across Maharashtra, 23 new Omicron cases were detected on Thursday. Thirteen of them are from Pune district, two from Osmanabad, and one each from Thane, Mira-Bhayander, and Nagpur.