Of the 14,378 coronavirus infections reported in the country till Saturday morning, 4,291 cases in 23 states and Union Territories are linked to the Markaz event held in Delhi's Nizamuddin area in March, the Union health ministry said.
By Saturday evening, the death toll due to coronavirus infection rose to 488, while the number of cases climbed to 14,792, according to data provided by the Centre.
However, a PTI tally of figures reported by various states as on Saturday evening showed 14,848 infections and at least 503 deaths.
There has been a lag in the Union Health Ministry figures, compared to the number of deaths announced by different states, which officials attribute to procedural delays in assigning the cases to individual states.
At a daily media briefing about the COVID-19 situation in the country, Joint Secretary in the Health Ministry Lav Agarwal said most of the Markaz event-related cases have been found in states with high burden of the disease, such as Tamil Nadu (84 per cent), Telengana (79 per cent), Delhi (63 per cent), Uttar Pradesh (59 per cent) and Andhra Pradesh (61 per cent).
"A total of 4,291 COVID-19 cases or 29.8 per cent of the 14,378 coronavirus infections reported till Saturday morning are linked to the Tablighi Jamaat congregation," he said.
The health ministry official also said in some states which have reported fewer COVID-19 infections, also had cases with links to the Markaz event.
The only coronavirus case reported in Arunachal Pradesh till now is related to the Markaz event. Similarly, 32 of the 35 cases reported in Assam and 10 out of 12 cases from the Andaman and Nicobar Islands are linked to the same congregation, he said.
"The reason I drew your attention to this event is to highlight that even if one person does not follow the guidelines of social distancing and lockdown, the entire country has to suffer the consequences," Agarwal said.
The mortality rate in COVID-19 cases in India has been around 3.3 per cent, he said, adding 14.4 per cent of the deaths are between 0-45 years, 10.3 per cent between 45- 60 years, 33.1 per cent between 60-75 years and 42.2 per cent fatalities among people aged 75 and above.
"We see that 75.3 per cent deaths have been among those aged 60 or above and in 83 per cent cases there were co-morbidities," Agarwal said and reiterated the elderly and those with co-morbid conditions are at high risk.
About containment strategies implemented along with the lockdown, Agarwal said field-level actions are fetching positive results in several places.
"A positive trend has been noted in 47 districts of 23 states and UTs. Kodaggu in Karnataka is a new district added to this list along with Mahe in Puducherry that has not reported any fresh cases during the last 28 days," the official said.
22 new districts in 12 states have not reported any fresh case in the last 14 days. These districts include Lakhisarai, Bhagalpur and Gopalganj in Bihar, Udaipur and Dholpur in Rajasthan, Pulwama in Jammu and Kashmir, Rohtak in Haryana and Vishakhaptnam in Andhra Pradesh, Agarwal said.
He, however, stated that Patna in Bihar, Nadia in West Bengal and Panipat in Haryana where there were no COVID-19 positive cases in the first two weeks, have now reported incidents of the infection.
"We have to be on continuous vigil to fight this battle," the official said.
The joint secretary also said protocol for using rapid antibody test kits have been shared with the states by the Indian Council of Medical Research (ICMR).
"Rapid antibody test kits are to be used in hotspots. It can also be used for surveillance and for epidemiological purposes in such areas where COVID-19 cases have not emerged so far.
"RT-PCR test is the gold standard for frontline test and antibody test cannot replace this. Utility of rapid antibody test is primarily for assessing prevalence of infection in a particular area," he said.
According to the ICMR protocol, the official said, only those showing symptoms of influenza-like illness such as fever, cough and cold for a week or more in hotspot areas should be made to undergo rapid antibody test.
Those found positive must be quarantined for at least for seven days and contact tracing should be initiated. Those who turn out negative should be in home quarantine for a week.
"RT-PCR test should be done to confirm COVID-19 if clinical suspicion is high," Agarwal said.
Asked if ICMR was doing a randomised control trial to assess the efficacy of hydroxychloroquine (HCQ) in COVID-19 treatment, Head of Epidemiology and Communicable diseases at ICMR Dr Raman R Gangakhedkar said it is an observational study, not trial.
Around 480 patients will be enrolled and it will go for eight weeks, he said.
Dr Gangakhedkar said the ICMR has launched a study on the side-effects of HCQ using data from some health care workers who used the drug.
"The average age of the workers was 35 and the most visible side effects abdominal pain (10 per cent), nausea (6 per cent) and hypoglycemia (1.3 per cent).
"Twenty-two per cent of these healthcare workers who took HCQ had diabetes or blood pressure, vascular or respiratory illnesses. They started taking the drug out of the fear of contracting the disease," he said.
Dr Gangakhedkar said AIIMS is conducting studies to assess the prevention and healing impact of HCQ on COVID-19.
"In some places HCQ consumption is not that high. So it impacts the study design and collection of data. We are facing difficulty in finding a homogenous population," he said.