CHENNAI: Tamil Nadu is yet to officially announce the start of the third wave of Covid-19, but public health experts and doctors say there are enough strands of scientific and statistical evidence to show that the epidemic curve has set in.
Key epidemiological factors infection growth rate, rate of transmission, doubling time and hospital occupancy indicate the epidemic curve is rising steep.
Fuelled by the fast-spreading Omicron variant, Covid-19 cases continued to increase on Thursday with 6,983 new cases in Tamil Nadu, most of them from Chennai, Chengalpet, Tiruvallur, Coimbatore and Vellore districts.
The R-naught or infection transmission rate in Chennai soared to 3.1 from less than 1 in the first week of December. During the same period, R-naught in the state increased to 2.43 from 0.96. If the R0 is three, each new case of a disease will produce three other infections. “With any R value greater than 1 the infection will increase, spreading through the population. The swift increase in this number shows that daily cases will continue to grow exponentially,” said National Institute of Epidemiology deputy director Dr Prabhdeep Kaur.
The rising R-naught has led to swift growth in infection rate. The average daily cases reported by Chennai on Wednesday was at least 7.3% more than what the city had reported a month ago. On Thursday — when new cases in Chennai increased to 3,859 — the growth rate went up to 8.7%. On an average the city reported 1,536 cases every day compared to 125 cases a month ago.
During the same period the average cases in the state increased to 2,934 from 719. “For the daily infections and fresh cases to come down, the effective R must go below one,” Dr Kaur said.
The rapidly growing infection rate has reduced the doubling time. Chennai, which has so far reported 5.7 lakh Covid-19 cases since March 20, can double it in just 258 days. On New Year’s day it was more than 1,000 days. In the state, the period has dropped to 600 days from more than 2,000 days on January 1 and 2600 days a month ago.
In addition to the shrinking of doubling time, the state is reporting an increase in test positivity rate (TPR). “Over the last few days, districts like Chennai, Chengalpet and Tiruvallur have increased tests. The average test positivity rate has also increased. This is because of two reasons. First, we know the infection itself has increased, secondly the percentage of people reporting to labs with symptoms or suspicion have increased substantially,” said director of public health Dr T S Selvavinayagam.
Results of nearly four out of every 100 patients tested in Chennai return positive compared to less than one a month ago. Along with Chennai, the test positivity rate is high in Chengalpet (3.2%), Tiruvallur (2.2%) and Tuticorin (1.9%). However, the average test positivity rate in the state is 1.5%.
“The percentage of people coming into hospitals from the total pool of active cases have come down,” said Director of Medical Education Dr Narayanababu R. For instance, of the 1,189 active cases in Chennai, 536 (45%) were admitted to hospitals. On Wednesday, out of the 7,878 patients, 2008 (25%) were in hospitals.
“While we track, test, isolate and vaccinate people, we want people to mask up and maintain Covid norms. We want to minimise clusters,” said health minister Ma Subramanian.