Watch out for that cough: What the latest data on India’s coronavirus testing tells us

A research paper published on Friday by a study group of the Indian Council of Medical Research provides the clearest statistical window to the novel coronavirus testing situation in India.

The group, which features both government scientists and independent experts, examined anonymised data of 1,021,518 people tested for Covid-19 between January 22 and April 30. Of these, 40,184 people tested positive – a positivity rate of 3.9%.

Beyond the aggregate numbers lie significant insights.

Here are five takeaways from the study.

1. Asymptomatic contacts account for the highest proportion among those tested and confirmed

India’s testing strategy has gradually expanded to include a range of people: those with recent international travel history, symptomatic contacts of confirmed cases, asymptomatic family contacts of confirmed cases, health workers, hospitalised patients with severe acute respiratory infections or SARI and patients with influenza-like-illness or ILI in hotspot areas.

Data on how many people have been tested and confirmed in each category can tell us whether the disease is spreading among those with a history of contact with confirmed cases or among those who lack one.

Unfortunately, testing category data is not available for 578,816 people – or 56.7% of those tested for Covid-19 in India.

Among the people for whom data is available, asymptomatic contacts of laboratory-confirmed cases accounted for the largest group to be tested (19.6%) and the largest group of positive cases (25.3%).

In contrast, patients with respiratory infections who do not have any clear contact history with confirmed cases form a smaller group – less than 14% of positive cases.

2. Positivity rate is higher among symptomatic contacts – and for women

While asymptomatic contacts account for the largest group tested, the positivity rate – the number of positive cases among every 100 cases tested – was higher among the symptomatic contacts.

For 100 symptomatic contacts tested, 10 returned positive. In contrast, only five of 100 asymptomatic cases tested positive. Put simply, the chance of a symptomatic contact testing positive was double that of an asymptomatic contact.

Among hospitalised patients with severe acute respiratory infection, six of 100 cases tested positive – the second highest positivity rate among the categories which had to be mandatorily tested.

3. Tripura has tested the highest number of contacts per person, Jharkhand the lowest

Nationally, the average number of contacts traced and tested per laboratory-confirmed case was found to be six. However, this number showed great divergence among states. While Tripura led with 328 contacts tested per positive case, Jharkhand was at the bottom of the table with 1.3 contacts tested per positive case.

Among the top ten states and union territories in terms of reported positive cases, the average number of contacts tested per positive case was more than the national average in Tamil Nadu (14.4), Uttar Pradesh (9.8). Telangana (8.1), Andhra Pradesh (7.7), Madhya Pradesh (7.6) and Rajasthan (6.3).

However, the authors did not have data on several people who were tested. When normalised for this missing data, the national average number went up to 20.4. State-wise, Tripura led once again with 1,387 contacts tested per positive case while Chandigarh with a corresponding number of 6.6 was at the bottom.

4. Cough was the most common symptom among confirmed cases

Among the confirmed Covid-19 cases who showed symptoms at the time of specimen collection, a cough was the most commonly reported symptoms: 64.5% had it.

This was followed by fever with 60% of the symptomatic positive cases running a temperature at the time of sample collection.

One-third of cases reported sore throat and breathlessness. Gastrointestinal symptoms such as abdominal pain, nausea, vomiting and diarrhoea were reported by less than 5% of people with symptoms.

5. Attack rate higher among men and highest among those in the 50-59 years age group

Demographically, people in the age group of 20-29 years accounted for the highest number of Covid-19 cases in India. But among those tested, older people were more likely to test positive – the age group of 60-69 reported the highest positivity rate at 5.4%.

Even at the level of the larger population, older people showed higher vulnerability. The attack rate per million population was the highest among 50-59 year olds (64.9%) and 60-69 year olds (61.8%). It was the lowest among those under 10 years (6.1).

Men accounted for nearly seven of every 10 coronavirus tests in India. However, women reported a marginally higher positivity rate (4.2 %) than men (3.8%).

The attack rate per million population was higher among men (41.6%) than women (24.3%).