Dengue cases shoot up in Delhi in a week, end of rains could add to spike

The national capital’s annual tryst with dengue may have been delayed this year because of persistent rains, but with 106 cases being reported in the past week (ending September 15) alone, the first entirely dry week in almost two months, healthcare workers and experts say they expect to see an increase in the number of infections soon.

Thus far this year, 243 dengue cases have been reported, according to the latest report by the South Delhi Municipal Corporation (SDMC), which compiles infections data after taking inputs from three other corporations: New Delhi, East Delhi and North Delhi municipal corporations. October and November are usually the peak dengue season.

Last year, 1,177 dengue cases were reported in Delhi by the third week of September. In 2016, the number was 804.

“So far, the number of cases of dengue and indeed all the three mosquito-borne illness that are usually reported from Delhi is less than previous years, but the numbers might go up,” said a municipal health official on condition of anonymity.

The dry spell may be the reason behind the sudden spike in numbers over the past week.

“When there is continuous rainfall, the mosquito larvae get washed away. It is usually during the dry spells after the rainfall when there is a lot of water accumulation that the breeding starts,” said Dr Sarala K Subbarao, former director of National Institute of Malaria Research and former consultant on vector-borne diseases with Indian Council of Medical Research.

“For the past 10 days or so, there has been no rain in Delhi; this may be the reason why the numbers have gone up now,” she added. The numbers might also be less this year because of the milder strain of dengue DENV 3 virus which has been in circulation for three years now.

“With the same serotype of dengue in circulation for the last three years, immunity in the population may have built up,” said Subbarao.

“This could be a reason why dengue cases having the same serotype are low this year,” she said.

“The number of cases of vector-borne diseases reported from an area depends on several variables -- the amount and intensity of rainfall, the strain of the disease, etc.”

The strain has remained the same since 2016; in 2015 Delhi saw its worst-ever dengue outbreak that affected nearly 16,000 people and killed 60. That year, the deadlier DENV 2 and 4 strains which are associated with internal bleeding and a drop in platelet count were in circulation.

Civic officials said they are carrying out outreach and awareness campaigns like they do every year to combat mosquito breeding. “The corporation is leaving no stone unturned to ensure breeding control measures like spraying of insecticides and (ensuring) cleanliness. The domestic breeding checkers (officials who carry out door-to-door visits to warn and fine people over water accumulation) are making regular visits to sensitive areas to ensure no mosquito breeding takes place,” said Adesh Gupta, mayor of the north corporation.

The corporations also reported 13 cases of chikungunya during the week, taking the total to 60, and 30 cases of malaria, taking the total to 225.

First Published: Sep 18, 2018 08:47 IST