Two-year-old Sanjeev Yadav, whose parents hail from Bihar, has been found infected with the virus. Earlier on January 2, tests confirmed that one-year-old Sahabuddin Sheikh was also infected by the virus.

The National Polio Surveillance Programme (NPSP), after being advised by the state government, carried out two special polio immunisation drives in November and December last year in Kolkata, Howrah, North 24 Parganas and South 24 Parganas.

“The drives were carried out in places where a large number of migrants from Bihar and Uttar Pradesh live,” said Dr Dipankar Mukherjee, Regional Coordinator of NPSP.

The KMC has also identified the western fringes of the city — Garden Reach and Kidderpore areas in particular — that has a substantial population of migrant families, as a sensitive zone.

“Many a times it has been observed by the health department that residents of this area refuse to participate in the polio eradication drive initiated by the state government. More action is needed in the area,” said Mayor Bikash Ranjan Bhattacharya.

The main concern, however, is that the virus was detected in the stool of the patients, which makes the disease more susceptible to spreading. Children below five years of age are vulnerable to the attack of the virus. Sometimes the virus-infected stool can cause water contamination and enter the body of the child orally. In Yadav’s case, too, the polio virus was found in the stool.

“As the child had contracted infection in Darbhanga in Bihar and the transmission in Kolkata has not been proved, no special action is needed for Kolkata as of now,” Mukherjee, however, said.