Swab test results are taking around four days to arrive, a delay that could throw awry containment plans in the city as contacts of infected persons end up spreading the virus before they are isolated, corporation officials said.

A man from central Calcutta, identified as a suspect in the door-to-door surveillance drive carried out by the Calcutta Municipal Corporation (CMC) this week, was allowed to go home after his swab samples were collected at the New Town campus of Chittaranjan National Cancer Institute. The report is yet to arrive.

“The test reports were initially coming within 24 hours, or 36 hours at the most. I do not know why it is taking four days now,” a corporation official said.

Doctors said the man should have been admitted to a hospital and kept there till the test report arrived. Civic doctors have asked the man to be in home quarantine and avoid contact with family members.

“He should not have been allowed to go home after the test. What if the report is positive? He would likely have infected many more people by then,” a public health professional said.

The delay in reports would affect the fight against the novel coronavirus, public health professionals said.

Even if a person is in hospital during the wait for the test report, his contacts are not isolated till he tests positive. If the report takes long to come, it leads to delay in isolation of contacts and increases chances of the infection spreading,” a doctor said.

Public health professionals across the globe have said identifying and isolating patients and contacts is crucial in the fight against Covid-19. The protocol: test, identify a positive patient, isolate the patient and then isolate contacts to prevent the spread.

A senior health official denied any delay in arrival of test reports. But two orders issued by the health department tell a different story.

In an order dated April 24, the health department has authorised principals of medical colleges, where Covid-19 tests are being done, to hire data entry operators. The order was issued to “expedite the generation of reports of Covid-19 samples”.

Another order issued on April 25 said that “in order to further speed up the testing of swab samples for Covid-19 in the state, it may be necessary to run an extra shift in government laboratories so that testing and reporting can be done within the shortest possible time”.

Civic officials suggested equipping more laboratories, especially in and around Calcutta, to conduct the tests so that more people can be tested and reports come in time.

Ten laboratories in the city are conducting Covid-19 tests, according to the health department’s bulletin on Sunday.

“Calcutta has more cases and the districts most affected — North 24-Parganas, Howrah and East Midnapore — are also close to it. More testing facilities are needed in and around the city,” a doctor said.