Every one in four returning migrants from Delhi tested in Bihar for the novel coronavirus has been found positive, according to data released by the Bihar government. The state has tested 835 Delhi returnees, of which 218 or 26% have the infection.

“This was random sampling,” said Manoj Kumar who heads the state’s national health mission. “Symptoms were not taken into account while testing these people.”

Since last week, Bihar has been collecting random samples of asymptomatic migrant workers returning from other states. People returning from states with high case prevalence are being prioritised, said Manoj Kumar.

As of May 17, the state had tested 8,337 people who had come from outside the state. Of these, 651 tested positive – a positivity rate of 8%. Those returning from Delhi account for the largest share of these 651 cases.

The positivity rate among migrants returning from other states is much lower. For every hundred people returning from West Bengal tested, 12% were positive. The corresponding number for Maharashtra is marginally lower at 11%.

Infection on the way, says Delhi

Does the higher positivity rate among migrants returning from Delhi indicate a greater spread of coronavirus in the national capital than currently estimated?

Delhi state officials deny this. “While 26% is no doubt a high number, these people would have picked it up during the journey back, not in Delhi,” said a senior official of the state’s health department, requesting anonymity. Asked about the possibility of community transmission, the official said: “Delhi does not have such a scenario. It is not possible.”

Delhi has so far reported 10,054 positive cases. The official said the state conducted random testing at health facilities last week and found no incidences of community transmission. “We conducted tests on low-risk groups such as pregnant women and other people coming into our hospitals who had no symptoms and were not contacts of confirmed cases and did not find even a single positive case,” the official claimed.

Cases rise in Bihar

In Bihar, the return of migrants has significantly raised the number of coronavirus cases. More people have tested positive in the state in the past 10 days than in the previous two months.

After the Centre lifted restrictions on the movement of stranded workers on April 29, thousands of migrant workers stranded in their places of work have poured into Bihar, most of them by trains, but also in buses and on bikes and cycles. Others have just walked back home.

The state has so far received 300 trains ferrying its residents from across the country, said Pratyaya Amrit, principal secretary of the state’s disaster management department that is overseeing the repatriation. Another 500 trains are expected to come in over the next week, said Amrit.

Around 25,000 people have come from Delhi in these trains so far. That apart, officials say a large number of people from the capital have also come using other modes. On an average, the state sees around 3,000 people coming in through the various land borders each day, said another state official.

Passengers arrive at New Delhi station to take their trains. Credit: Kamal Kishore/PTI

The containment plan

Spooked by the high rate of positivity among the incoming migrants, Bihar is now drawing up new plans.

“We have drawn the attention of the concerned states to this and asked them to ensure immaculate pre-boarding screening,” said Sanjay Kumar who heads Bihar’s health department.

Locally, the state now will now segregate incoming migrants on the basis of where they have come from. While earlier, everyone was put into a common block-level quarantine facility, now people will be divided into three categories, said Amrit.

The first category would comprise people from hotspot cites such as Mumbai, Pune, Surat, Delhi and Kolkata. “All of these people would be housed in block-level large isolation facilities,” said Amrit. “Each room in this facility would house two people.”

The second category of people would be those coming in from other parts of Maharashtra, Gujarat, Delhi and West Bengal. They will be put in a quarantine centre at the panchayat-level, said Amrit.

The third and final category of people would consist of people from remaining parts of the country and would be put up in quarantine facilities in their respective villages.

If people from the second and third categories exhibit symptoms during their quarantine period, they would be shifted to the first category, Amrit said.

The period of quarantine would be same for everyone: 14 days. “Ideally, we would have liked it to be 28 days, but any policy is contingent on capacity,” said Sanjay Kumar of the health department.

‘Community transmission’ in Delhi

While Bihar has been left scrambling by the high positivity rate among incoming migrants, what does it say about the situation in the originating states?

T Jacob John, one of India’s leading virologists, said while the numbers did appear alarming, they ought to be looked at in perspective. “A lot of these people who have tested positive are likely to have travelled together in groups,” he said. “So if two percent were infected in Delhi, by the time they reached Bihar it would have shot up to 25%.”

Epidemiologist Jayaprakash Muliyil, former principal of the Christian Medical College in Vellore, also cautioned against extrapolating the high prevalence rate to the rest of the population in Delhi. “Most of these migrants lived in cramped quarters, so naturally they are vulnerable than others living in more comfortable and larger spaces.”

Yet, both Muliyil and John agreed that this meant that the transmission level in Delhi was quite high. “Delhi has the virus and there is community transmission,” said John.

Passengers wearing protective masks wait outside a railway station in Delhi to board trains on May 12. Credit: Adnan Abidi/Reuters

Data deficiency

While Bihar found one positive patient for every four people it tested from Delhi, there is not enough publicly available data to arrive at the corresponding number for the population in Delhi. The state has so far tested around 1,40,000 samples, but there is no granular data available to filter repeat samples for the same individual to arrive at a positivity rate.

Even the state government does not have access to that data, according to the Delhi health official. “The labs report the data to ICMR (Indian Council of Medical Research) and the format set by them is number of samples tested,” said the official. “We need that data too [number of people tested as opposed to samples], but the system that the government of India has developed does not give us access to it.”

To get a better sense of the testing data, the official said the state was “building a type of customisation so that the patient ID [identity] is linked to the test sample”.

“It is an in-house exercise that started a week back,” the official added. “It is not complete yet.”