Asymptomatic cases also include healthcare workers in contact with positive cases without adequate protection, although these account for only 2.8% of positive cases. Between January 22 and April 30, more than 10.21 lakh people were tested for Covid-19, of which 40,184 or 3.9% were positive.
On April 21, ICMR had said 69% of positive cases were asymptomatic, which was a much higher number. However, till then only around four lakh samples were tested for Covid-19 in India and just 18,601 were positive. The latest study points out that testing has increased several times over the eight weeks from 250 individuals per day at the beginning of March to 50,000 per day by the end of April. A significant over 44% of positive cases have been identified as under “no specified” category.
Officials said the percentage of asymptomatic people is likely to be more as many have not been able to provide details properly. However, the spread in the wider population is being tracked by periodic increases in the ambit of testing with serological surveys of low and high risk categories being the latest measure. The study shows Covid-19 cases were most common among close contacts and affected men and the elderly more.
According to the study published in the Indian Journal of Medical Research (IJMR), of the 28.1% asymptomatic patients, 25.3% were direct and high-risk contacts of the positive cases. The attack rate (per million) by age was highest among those aged 50-69 years (63.3) and was lowest among those under 10 years (6.1). The attack rate was higher among men as 41.6 of them tested positive, while 24.3 of the women contracted the infection. Attack rate is people affected or positivity rate in a particular age group.
Among 12,810 cases with reported symptoms at the time of specimen collection, cough and fever were the most commonly-reported, while around one-third reported sore throat and breathlessness. Gastrointestinal symptoms such as abdominal pain, nausea, vomiting and diarrhoea were reported by less than 5% of cases, the findings show.
More than 71% districts of the 736 total districts in the country reported cases infected with the virus. States with the highest proportion of districts reporting positive cases included Delhi, Maharashtra, Kerala, Punjab, Haryana, Tamil Nadu, Andhra Pradesh and Gujarat. The states and UTs with the highest test positivity were Maharashtra (10.6%), Delhi (7.8%), Gujarat (6.3%), Madhya Pradesh (6.1%) and West Bengal (5.8%).