Health authorities on Wednesday recorded 3,525 more patients with the coronavirus disease, raising the number of “active cases” under observation or treatment in hospitals to 47,480, but researchers tracking the epidemic predicted the active cases could rise to 80,000 by May 20.

The new cases detected overnight have increased the country’s total confirmed Covid-19 cases to 74,281, of whom 24,386 have recovered and 2,413 patients have died, 122 over the past day, according to figures released by the health ministry.

The daily spikes — an increase of more than 3,000 new cases every day over the past seven days — likely reflect a slight increase in the effective reproductive number, or R, that scientists have calculated has increased to 1.29 from 1.27 on May 2, researchers said. “R” represents new cases that one infected person can cause.

“Under the growth pattern we’ve been observing, new cases on average are likely to continue increasing day after day,” said Sitabhra Sinha, a researcher at the Institute of Mathematical Sciences, Chennai, who has led an effort to analyse the epidemic patterns.The analysis by Sinha and his colleagues has now suggested that the number of active patients will increase to around 80,000 by May 20. This is a higher estimate than what Sinha’s own analysis and an independent forecast by the Indian Institute of Science Education and Research, Calcutta, had yielded last week.

Sinha said his analysis relies on day-to-day changes and thus lends itself to daily corrections with new data.

While the rising counts are expected, public health experts said, health authorities need to track local increases at the district level and map them with available hospital and intensive care unit infrastructure.

The health ministry had last week said the country had kept ready 305,000 isolation beds for confirmed Covid-19 patients, 99,492 oxygen-supported beds and 34,076 intensive care unit beds.

Less than 5 per cent of patients have required intensive care thus far but, a public health specialist said, districts with large outbreaks could feel the strain if they are not adequately prepared with required beds.

The health ministry’s Wednesday figures also show a slight dip in Bengal’s case fatality rate — the number of deaths divided by the number of confirmed cases — from 10 per cent to 9.1 per cent.

Among states with similarly large outbreaks of more than 1,000 confirmed cases, Gujarat has the second highest case fatality rate of 6 per cent, followed by Madhya Pradesh at 5.6 per cent. The country’s average case fatality rate is 3.3 per cent.

Three states make up over 63 per cent of the current active cases — Maharashtra with over 18,300 patients, Tamil Nadu with over 6,500 patients and Gujarat with over 5,100 patients. Maharashtra, Gujarat and Madhya Pradesh account for 73 per cent of the country’s total Covid-19 deaths.