Asymptomatic family contacts form bulk of COVID-19 cases in India: ICMR study

Nearly 40,000 individuals out of 1 mln tested positive for SARS-CoV-2 between Jan 22 and April 30, 2020. About 25.3% of them were asymptomatic family contacts of COVID-19 cases

By Banjot Kaur
Published: Saturday 30 May 2020

At least a quarter of the 40,184 individuals who tested positive for the novel coronavirus SARS-CoV-2 in India between January 22 and April 30, 2020 were asymptomatic family contacts of confirmed COVID-19 cases, according to a paper published in the Indian Journal of Medical Research (IJMR).

At least a million people across India have been tested for the virus in the given time. About 10.6 per cent of the positive cases were found to be symptomatic family contacts of COVID-19 cases. This was followed by patients with severe acute respiratory illness (SARI) (10.5 per cent) and influenza-like illness (3.0 per cent); asymptomatic healthcare workers (2.8 per cent); and symptomatic healthcare workers (2.4 per cent). 

A total 2,082 healthcare workers tested positive for the virus in the given duration. This is the first time that number of healthcare workers infected has been put in the public domain.

Lav Agarwal, joint secretary, Union health and family welfare ministry, had earlier denied giving these figures saying that healthcare workers comprised only a “minuscule” fraction of COVID-19 cases.  

More contacts tested

The number of contacts (family or otherwise) of COVID-19 positive cases who were tested for every confirmed case in India was 6, according to the findings.

The top 10 states that tested a relatively greater number of contacts were Tamil Nadu (14.4), Uttar Pradesh (9.8), Telangana (8.1), Andhra Pradesh (7.7), Madhya Pradesh (7.6) and Rajasthan (6.3).

Only two out of five states (Maharashtra, Tamil Nadu, Delhi, Gujarat and Rajasthan) — that have maximum cases positive to the virus in the country — figured in the list.

In other words, these states are still testing a relatively fewer number of contacts than their peers; while Maharashtra tested 2.3 contacts per confirmed case, Delhi and Gujarat tested 2.1 and 4.8 contacts respectively.

Jharkhand had the lowest testing rate in the category. 

The overall positivity rate in the period of this analysis in India was 3.9 per cent. The seven-day rolling average of positivity rate was 3-6 per cent.

The states that had higher positivity rate than the national average during this period included 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).

Among them, only MP figured in the list of states that tested more contacts per positive cases than the national average in the given duration. 

Community transmission

The paper highlighted that the proportion of detected cases reporting any international travel decreased over time, thereby indicating that there were more home-grown cases.

So does this point out to community transmission?

“Because the testing criteria, except for SARI, require exposure to a positive COVID-19 case, we are uncertain about the transmission among unlinked individuals in the community,” the paper said.

In other words, since people other than the contacts of confirmed cases are not being tested, the papers of the authors said they could not conclusively deny or confirm community transmission.

However, the paper also read: “The surveillance data had a large proportion of tests with missing information on exposure history,” implying that for a large number of cases, the travel / contact history could not be traced. This could further imply that infection had seeded within the community unlinked to international travel / contact history.

India is the only country that has had nearly 175,000 cases as on May 31,2020 and is still silent on community transmission.

Range of symptoms

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 and 60 per cent respectively).

A third of the cases reported sore throat and breathlessness. Gastrointestinal symptoms were reported by less than 5 per cent cases, the paper stated. 

While loss of smell and taste has been reported as a potential symptom in a number of confirmed cases globally, the IJMR paper did not say anything on this.

The attack rate of the virus — the number of individuals affected per million population — was found to be the highest among those aged between 50 and 69 years.

While the positivity rate in women was reported to be slightly more than males, the attack rate was higher among males (41.6 per cent) than females (24.3 per cent).

The secondary attack rate (number of individuals per million population affected in a particular setting, for example, a household) was found to be 6 per cent in India. 

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