Asymptomatic infections: India's next big coronavirus challenge

On May 25, an autorickshaw driver from Belur in Kerala's Kasargod was admitted to a hospital after getting hit on the head by a falling jackfruit. During routine tests conducted before surgery, he tested coronavirus positive. The Indian Express reported Dr K. Sudeep, superintendent of the Pariyaram Medical College in Kannur, as saying: “Our protocol dictates that we subject everyone who require immediate surgery to the COVID-19 test, just to be sure. That is when he tested positive.”

The spread of asymptomatic cases of coronavirus has always been a point of concern for India. On April 20, the health ministry warned that 80 per cent of all coronavirus patients were asymptomatic or showed mild symptoms. "On the basis of worldwide analysis, out of 100 coronavirus patients, 80 per cent are asymptomatic or show mild symptoms. Around 15 per cent patients turn into severe cases and five percent cases turn into critical cases," said Lav Agarwal, Joint Secretary, Health and Family Welfare, at the daily press briefing.

On April 21, Raman R. Gangakhedkar, Head of Epidemiology and Communicable Diseases at Indian the ICMR, said: "[In India] Among the total coronavirus tests conducted so far, 69 per cent were asymptomatic cases and 31 per cent were symptomatic cases. Which means for one positive patients when we initiated contact tracing, on an average we found three or four asymptomatic patients," he said.

Mid-April, the Hindustan Times reported that around 75 per cent of the total COVID-19 cases in Punjab, 50 per cent in Karnataka, 65 per cent in Maharashtra and 75 per cent in Uttar Pradesh were asymptomatic. Nearly 82 of the COVID-19 patients in Assam (reported at the time) were asymptomatic, said health minister Himanta Biswa Sarma.

Now, a new study has estimated that at least 28 per cent of 40,184 people, who had tested positive for COVID-19 between January 22 and April 30 in India, were asymptomatic. The study was published in the journal Indian Journal of Medical Research (IJMR). Scientists have raised alarm over the findings. "However, the proportion of the asymptomatic infected people could be much more than the 28.1 per cent and this is a cause of concern for us," said Manoj Murhekar, director of the ICMR's National Institute of Epidemiology and one of the authors of the study said, reported PTI. 

The study also found that proportion of positive cases was highest among symptomatic and asymptomatic contacts, two or three times higher than among those with severe acute respiratory infection, or those with an international travel history or healthcare workers. This neatly complements a detailed investigation of the cluster of SARS-CoV-2 infection among 16 Italian tourists, which found that the novel cornonavirus has a higher rate of transmission among close contacts. 

The attack rate (number of people exposed who are sick divided by the number of people exposed) per million, taken by age, was highest among those aged 50-69 yr (63.3) and was lowest among those under 10 yr (6.1). The attack rate was higher among males (41.6) than females (24.3).

The ICMR, on Saturday, ICMR, advised states to conduct sero-survey to assess the proportion of population including asymptomatic individuals exposed to coronavirus infection.

Below are a few findings from the report:

How did India conduct testing for the coronavirus?

1. Between January 22 and April 30, 2020, a total of 1,021,518 individuals were tested for SARS-CoV-2 (coronavirus), of which 40,184 (3.9 per cent) tests were reported positive.

2. Testing increased from about 250 individuals per day in the beginning of March to 50,000 per day by the end of April 2020. This represented a 200-fold increase in testing over eight weeks.

3. In all, 729 out of 736 districts (99 per cent) reported any testing.

4. The testing frequency ranged from 182/ million in Manipur to 2149/million in Delhi.

5. Higher than national average tests were conducted by states Andhra Pradesh (1721 tests/million), Tamil Nadu (1468 tests/million), Jammu and Kashmir (1417 tests/million), Rajasthan (1329 tests/million), Haryana (1308 tests/million), Tripura (1251 tests/million), Gujarat (1133 tests/million), Maharashtra (1070 tests/million), Karnataka (1011 tests/million), Himachal Pradesh (889 tests/million) and Kerala (814 tests/million).

Symptoms, age/gender of the COVID-19 patients

1. Among the 12,810 cases with reported symptoms at the time of specimen collection, cough and fever were the most commonly reported symptoms (64.5 per cent and 60 per cent respectively).

2. Around one-third of cases reported sore throat and breathlessness.

3. Gastrointestinal symptoms such as abdominal pain, nausea, vomiting and diarrhoea were reported by less than 5 per cent of cases.

4. Attack rate (per million population) was the highest among those aged 50-59 and 60-69 year olds (64.9 per cent and 61.8 per cent, respectively) and was lowest among those under 10 yr (6.1 per cent). While the per cent positive among tested was slightly higher among females (4.2 vs. 3.8 per cent), the attack rate (per million population) was higher among males (41.6 per cent)

Profiles of those who tested COVID-19 positive in India in the time frame:

1. Symptomatic international travellers: 523 cases (1.3 per cent).

2. Symptomatic contacts of laboratory confirmed cases: 4,257 cases (10.6 per cent).

3. Symptomatic healthcare workers 947 cases (2.4 per cent).

4. Hospitalised Severe Acute Respiratory Infection (SARI) patients: 4,204 cases (10.5 per cent). 

5. Asymptomatic direct and high risk contacts of laboratory confirmed case—family members: 10,160 cases (25.3 per cent).

6. Asymptomatic healthcare workers in contact with confirmed case without adequate protection: 1,135 cases (2.8 per cent).

7. ILI (Influenza-like illness) identified in hot zones: 1,199 cases (3.0 per cent).

That is, more 28 per cent of the cases were asymptomatic. Positivity was highest among the symptomatic contacts (10.3 per cent) and SARI patients (6.1 per cent). Of the 40,184 positives, 25.3 per cent were asymptomatic family contacts, 10.6 per cent were symptomatic contacts and 10.5 per cent were SARI patients.

State-wise trends

1. States with the highest proportion of districts reporting positive cases included Delhi, Maharashtra, Kerala, Punjab, Haryana, Tamil Nadu, Andhra Pradesh and Gujarat. 

2. States/ UTs with the highest test positivity were Maharashtra (10.6 per cent), Delhi (7.8 per cent), Gujarat (6.3 per cent), Madhya Pradesh (6.1 per cent) and West Bengal (5.8 per cent).

Tackling asymptomatic cases:

The ICMR has advised states to conduct sero-survey to identify asymptomatic individuals exposed to coronavirus infection. A sero-survey involves testing of blood serum of a group of individuals for the presence of antibodies against that infection to know who has been infected in the past and has now recovered. People from 70 districts will be tested for COVID-19 at random to check whether they have developed antibodies against the infection even though they remained asymptomatic.

Depending upon the level of sero-prevalence of infection, appropriate public health interventions can be planned and implemented for prevention and control of the disease, the Indian Council of Medical Research (ICMR) said.

The health research body has suggested that the blood serum samples of high risk or vulnerable populations like health care workers, frontline workers, immune-compromised individuals, individuals in containment zones, police personnel among others should be tested for COVID-19 antibodies.