The number of dengue cases in Calcutta has risen from 255 (till August 3) to over 380 (till August 24), officials of the Kolkata Municipal Corporation (KMC) said.

According to the civic body officials, 128 fresh cases were reported within 21 days. “It is a reason to be cautious, though the surge is not alarming,” said an official.

KMC’s vector control teams have been instructed to focus on under-construction sites and identify probable mosquito breeding sites so that they can be destroyed.

“From January to August 24, 383 dengue cases were reported in the Calcutta municipal area. In the past week, 40 new cases were reported,” the KMC official said on Friday.

An official had earlier said that 290 dengue cases were reported in the city between January and August 3.

“We are apprehending a spike in the dengue cases because our experience shows that dengue cases rise in late August and September,” said an official.

The civic body has identified seven wards as dengue-vulnerable based on the number of cases reported since January. The wards include neighbourhoods such as Sunny Park and Queens Park in Ballygunge, along with parts of Lake Gardens, Topsia, Picnic Garden, Kidderpore, Jodhpur Park, and Bhowanipore.

An official said that no new neighbourhoods have been added to the list of vulnerable wards in the last fortnight.

“Several cases were reported from Sunny Park within a short period of time earlier. We call such a phenomenon clustering. We have not noticed any clustering in Sunny Park in the last fortnight,” said a KMC official.

Two men are known to have died of dengue in the Calcutta municipal area this month.

Swaroop Mukerji, 75, a resident of Sunny Park in Ballygunge, died on August 9 after a brief bout of fever.

Arijit Das, 35, from Gabtala Lane in Behala Parnasree, died of dengue on August 14.

Earlier, on June 21, 13-year-old Saroni Banerjee, a resident of Dum Dum Cantonment under the Dum Dum Municipality, had also died of dengue.

KMC sources said the number of malaria cases reported in the city between January and August 24 stood at 1,605.

The number of malaria cases reported in the city till August 10 was 1,156, which means 449 fresh cases were reported within 14 days.

“We have requested the awareness campaign teams to communicate messages regarding the prevention of water accumulation in key areas across all neighbourhoods. The teams have been instructed to convey the complete message in one location before proceeding to the next site to deliver the message there,” said an official.