CHENNAI: The data on the doubling time for COVID-19 cases in the city, especially in the zones including Royapuram and Tondiarpet, may indicate that the transmission is low in several areas in the city which were earlier considered a challenge by the state government and the city corporation.
In Royapuram, the doubling time is at 57.1 days as on July 7, 32.7 days in Tondiarpet and 32.4 days in Thiru Vi Ka Nagar, considered a fair indication for the slow transmission in these regions.
"There is clear evidence of data, showing good results in Chennai. A doubling rate above 14 days is usually recommended," Madhusudhan Reddy, Joint Commissioner (Health), Chennai Corporation told Express.
The doubling time is calculated using a seven day moving average. It takes into account the cumulative number of COVID-19 cases on the seventh day and the first day in order to calculate the doubling time.
While a higher doubling time may be considered an indication of the slow transmission of the virus in the respective zones, it is based on certain assumptions - for instance that the testing and detection patterns and the overall strategy and resources are more or less the same in these zones.
"In the case of Royapuram for instance, when we plot the doubling time on a graph,the trend seems to be going upwards which is a good sign. It means the transmission may be less," said Dr P Ganeshkumar Assistant Director & Scientist ICMR National Institute of Epidemiology.
"This shows that the public health measures undertaken by the city corporation such as increased testing, door to door surveillance, fever camps and lockdown has impacted the doubling rate," he added.
While the doubling time for the city itself was 25.4 days, other zones like Teynampet, Madhavaram, Perungudi, Kodambakkam, Anna Nagar, Manali and Thiruvottiyur have the doubling time higher than that of the city's.
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However, some zones such as Adyar, Ambattur, Sholinganallur, Valasaravakkam and Alandur have doubling times which were lower than that of the city's. "In some of these areas, the case load has increased only recently. So measures are being taken there too and will be soon brought under control," the Joint Commissioner said.
The three main factors that the city corporation attributes to the present doubling rate is the lockdown, testing and surveillance, according to corporation officials. "Apart from intensive identification and isolation of positive cases, we have doubled the number of tests and also set up fever clinics. The turn out at a single fever clinic is 70-75 on average in a two-hour period," said Reddy.
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