As Telangana continues reporting a surge in the number of COVID-19 cases, new data from the Indian Council of Medical Research (ICMR) sheds light on the prevalence of secondary infections in the state. According to the ICMR report, the state has been showing one of the highest rates of secondary attacks.
Secondary attack rate is a term used by epidemiologists to refer to individuals who have been infected after being exposed to those with a positive diagnosis of a disease. In this case, contacts of individuals who have tested positive for SARS-CoV-2, the virus which causes COVID-19, who then later develop the infection themselves, are the ones who fall under the category of secondary infections.
The report looked at data of persons infected and tested between January 22, 2020 and April 30, 2020.
As per the report, India’s average secondary attack rate is 3.9%. In other words, out of the 20 contacts who have been tested per confirmed COVID-19 case, 3.9% tested positive. In comparison, Telangana shows an average secondary attack rate of 5.6% for every 14 or so immediate contacts who have been tested. Though the national average has been based on 20 contacts tested, given Telangana’s low rate of testing the infectivity rate was based on 14 contacts.
On a national level, Chandigarh has reported the highest secondary attack rate of 11.5%, followed by Maharashtra with 10.6%, Delhi reporting 8.8%, Madhya Pradesh at 6.7% and Gujarat at 5.8%.
The secondary attack rate for the other south states is below the national average. Tamil Nadu has an average secondary attack rate of 2.1%, Kerala is at 1.1%, Andhra Pradesh has an average of 1.1% and Karnataka has a rate of 0.9%.
Speaking to TNM on the condition of anonymity, one official from the Institute of Preventive Medicine (IPM) in Hyderabad, stated that with an adjusted infectivity rate using estimation models to account for 20 contacts, it could be determined that the average would come out to be a little over 7% in Telangana. This is nearly twice the national average.
“To get a better understanding of how widespread the cases are and to understand how many people are truly infected and at risk, there needs to be more testing. Without that, a lot of the data will remain skewed. Even though the number of tests being done is low, we are seeing that the secondary attack rate is high, which is very concerning. It brings into question how many cases we would actually be seeing if testing measures were increased,” adds the source.
It is also important to note that the Telangana government had last released the number of total tests done on May 17 and has been called out for its lack of transparency regarding this data on multiple occasions.
The ICMR report also stated that between January and April, a total of 7,593 individuals (both symptomatic and asymptomatic) who were contacts of someone who’d tested positive were also tested. Furthermore testing was done on a little more than 5,000 individuals who may or may not have shown symptoms, but fell into certain criteria for testing, for a total of 18,519 tests done. Of the tests done, 951 were found to be positive for SARS-CoV-2, of which 752 individuals were immediate contacts of a someone who was known to be diagnosed with COVID-19.
It was also found that the highest percentage of positive cases were reported among those between the ages of 50 and 69.
Image courtesy: Indian Journal of Medical Research