BENGALURU: The spread of Covid-19 infection in the state is significantly higher in the symptomatic cases though asymptomatic persons too can transmit the virus.
This was one of the major findings of a study conducted in Karnataka by health experts from the National Institute of Mental Health and Neuro Sciences (NIMHANS), Indian Institute of Public Health, Bengaluru, Public Health Foundation of India and State Surviellance unit, Directorate of Health and Family Welfare, Government of Karnataka.
The study titled “Epidemiology of SARS-CoV-2 infection in Karnataka State, South India: Transmission dynamics of symptomatic Vs asymptomatic infections”, included the cases reported from March 8 to May 31. Dr Giridhar R Babu, Head of Lifecourse Epidemiology at the Public Health Foundation of India and member of the Karnataka expert committee of Covid task force, said, “Though it was noted earlier that the role of asymptomatic persons in transmission was minimal, there have been cases where there is a spread of infection through their contacts.
But the main focus of the study is specifically on how the symptomatic persons have driven the transmission.
"In the study we can clearly see that symptomatic cases are the potential spreaders. And we need to trace them at the earliest to prevent more infection and deaths.”
The study stated in the total number of clusters, majority was through a symptomatic patient. The secondary cases manifesting overt clinical illness was higher when the index case was symptomatic.
Of the 545 secondary cases, 43 were symptomatic and 616 were asymptomatic.
The 43 symptomatic cases resulted in the transmission of infection to 659 people giving a mean secondary attack rate of 17·03.
On the other hand, the 616 asymptomatic source cases contributed to a total of 504 secondary infections giving a mean attack rate of 3·01.
Dr Babu said, “Analysis suggests that symptomatic cases were the prime drivers of the SARS-CoV-2 transmission in the state. Now the focus should be on symptomatic people being tested first. The idea is to trace and test symptomatic individuals at the earliest.” As per the findings, of the 3,404 positive cases, 3,096 (91%) were asymptomatic while 308 (9%) were symptomatic.
The report stated that of the 3,404 cases, 158 (5%) had comorbidities such as diabetes, hypertension, chronic renal disease and malignancy. But the occurrence of comorbidities was ten-fold higher in symptomatic cases (87/308: 28·2%) compared to asymptomatic ones.
The overall case-fatality recorded in Karnataka was 1.6% with symptomatic cases accounting for 87%. An interesting insight was that even mortality amongst asymptomatic cases was only 13%.