Delhi: With dip in temperature, mosquito breeding and fresh dengue cases go down

A senior public health official from the South Delhi Municipal Corporation (SDMC), the nodal agency for vector-borne disease data collection, said studies show a significant dip in mosquito breeding metrics and mosquito density.

After adding more than 2,500 cases last week, the dengue crisis in Delhi is on a downturn due to the fall in temperatures, which has limited mosquito breeding, doctors and health department officials said.

Delhi has so far registered 5,277 dengue cases. In picture - Civic body worker fumigates at Pandav Nagar Market area in New Delhi. (HT File Photo)

A senior public health official from the South Delhi Municipal Corporation (SDMC), the nodal agency for vector-borne disease data collection, said studies show a significant dip in mosquito breeding metrics and mosquito density.

“The anopheles and aedes aegypti mosquitoes prefer temperatures above 30 degrees Celsius. Once the temperature drops to about 20°C, they become less active in the open and cannot function at temperatures below 10°C,” said the official.

The official did, however, voice caution and asked people to be check stagnant water in their vicinity for mosquito breeding.

The India Meteorological Department (IMD) said Delhi recorded a minimum temperature of 9.8°C on Sunday, which is three notches below normal.

The city has so far registered 5,277 dengue cases (the most since 2015), according to the last update issued by the city’s civic bodies on November 13, and nine fatalities of the vector-borne infection. The municipal corporations release weekly dengue data every Monday, recording numbers for the previous week.

Hospitals also said the dengue caseload has dropped over the past week-and-a-half.

Dr SP Byotra, senior consultant at Sir Ganga Ram Hospital and chairman of the facility’s department of medicine, said that the number of dengue patients admitted in the hospital has dropped from 70-80 patients three weeks ago to less than 10 patients now.

“This can mainly be attributed to environmental factors. But people should continue to take precautions by preventing any water stagnation and wearing full-sleeved clothes,” he said.

Dr BK Tripathi, professor in the department of medicine at Safdarjung Hospital, said that the number of new suspected dengue cases is down by over half.

“Beside natural factors like a delayed monsoon, we have also observed that diseases like dengue and chikungunya follow a two-three year cycle, after which cases rise significantly. The caseload is likely to fall down next year,” he said.

Mosquito breeding detection data from infection hotspots shows that a lack of access to piped water is a major contributing factor to the rise in dengue cases. An analysis of 32 hotspots shows that 58.5% aedes aegyti larvae were found in water storage units such as drums, bucket, jeri cans, and 30.2% in peri-domestic units money plant vas, flower pots, bird-pots etc with smaller contributions from over-head tanks (5.4%), sumps (2.1%) and desert coolers (3.8%).

Delhi has this year already registered the most dengue cases since 2015. However, the annual count is likely to increase further at the end of the infection, as a large number of pending cases will be settled by that point.

Dengue, malaria and chikungunya were mandated as ‘notified diseases’ in mid-October, making it obligatory for all clinics and hospitals to report them to the state government. As a result of this, a large number of hospitals have reported details about previously unrecorded dengue cases.

“Before the notification, 36 hospitals under the ‘sentinel surveillance system’ used to share weekly data with the malaria headquarters. But now, corporations are getting data from 180 healthcare facilities. We are still receiving case details of patients from summer season. All these cases will be adjusted in annual cycle which will increase the annual count,” another senior public health official said.

Over the last one decade, Delhi has registered a dengue count higher than the current levels in 2010, 2013 and 2015. During the current year, Delhi had predominance of type II strain of the virus which leads to severe symptoms like haemorrhagic fever with shock. The civic bodies have so far confirmed 9 dengue deaths while several cases remain pending before the audit committee.