A 23-year-old woman who came to Calcutta from the UK and a 57-year-old man without any declaration of recent travel abroad have tested positive for Covid-19, taking the number of confirmed cases in the city to four.

The woman was sent to Beleghata Infectious Diseases Hospital from the airport on Friday. The man, on the other hand, was admitted to a private hospital in Salt Lake on Monday with complaints of fever and dry cough.

The family of the 57-year-old said, while submitting a self-declaration form at the time of admission, that he had not travelled abroad recently, an official at the Salt Lake hospital said.

But the form did not seek information on whether he had travelled to any Indian state from where Covid-19 cases have been reported.

Public health experts said if the man had indeed not travelled abroad or to any other Indian city, it could be a sign of community transmission of the infection. Community transmission is a situation where a chain of contact cannot be established between an infected person and any other infected person.

Once community transmission begins, the number of cases could go up very fast, public health experts said.

The 23-year-old student from Scotland, who became the third person in Bengal to test positive for Covid-19, complained of feeling feverish and a mild cough after landing at the airport from London on Friday. She had flown from London to Mumbai and from there to Calcutta.

The airport officials who screened the woman sent her to the Beleghata hospital, where she was admitted to the isolation ward.

“She acted very responsibly and herself went to the help desk at Calcutta airport. She was taken to the Beleghata hospital in one of the ambulances stationed at the airport,” a health department official said.

The woman asked her father, the driver of his car and a friend who had come to receive her at the airport to return home. The three were asked to report to Beleghata ID hospital on Saturday after the student tested positive for Covid-19.

“Doctors at the hospital said I should be in isolation for 14 days. I have spoken to my daughter. As of now, she is doing fine,” the student’s father told Metro.

Based on the ticket details, the health department is trying to trace 14 passengers on board the flight to Calcutta to quarantine them.

The 57-year-old man was admitted to hospital on Monday with fever and dry cough that had persisted since Friday. “His symptoms intensified on Thursday with acute respiratory distress and he was put on ventilator,” an official of the hospital said. “His samples were sent to both NICED and SSKM, one of which came positive. Another sample was sent on Saturday, which also tested positive.”

The patient has been shifted to an isolation bed for Covid-19.

“He had been in the ICU since admission. The distance between two beds in an ICU is more than three metres. Hence other patients are safe,” the official said.

All those who came in contact with the patient, including his family members, will be quarantined at home as per protocol, a health official said. “They would be tested also as per protocol and if they show any symptom of Covid-19, they would be isolated in hospital.”

The Salt Lake hospital has drawn up a list of 15 people, including cleaners and nursing staff, who came in contact with the man. All of them have been asked to stay in home quarantine for at least 14 days.

The health department on Saturday cancelled leaves of all personnel to combat Covid-19.

Only exigencies such as need for hospitalisation, severe illness, bereavement in family and childcare leave granted before Saturday’s order will be exempt.