Vector-borne disease surge: Malaria cases at 6-year high

To be sure, officials clarified that no deaths have been attributed to mosquito-borne diseases so far this year. However, health authorities warn that the actual case count may be much higher due to a large number of “untraced” or “incomplete” cases, which do not get added to the tally

As monsoon clouds retreat over Delhi, the city is once again battling a familiar seasonal problem -- the surge of vector-borne diseases. Municipal data shows that malaria infections have climbed to their highest in at least six years, while dengue and chikungunya continue to add to the city’s public health burden.

A municipal corporation worker fumigates a residential area in Delhi. (PTI)

According to the Municipal Corporation of Delhi’s (MCD) latest report dated September 29, Delhi has recorded 371 malaria cases so far this year, surpassing the corresponding figures for every year since 2019. The city had logged 363 malaria cases by the same period last year, 237 in 2023, 68 in 2022, and 66 in 2021.

While the number of dengue cases (759) remains lower than last year’s 1,229, officials say the city continues to report dozens of new infections every week. In the same period in 2023, Delhi had reported a much higher 1229 cases, while chikungunya cases this year stand at 61, in comparison to last year’s 43.

To be sure, officials clarified that no deaths have been attributed to mosquito-borne diseases so far this year.

However, health authorities warn that the actual case count may be much higher due to a large number of “untraced” or “incomplete” cases, which do not get added to the tally. The MCD report shows that, in addition to confirmed cases, 95 malaria and 223 dengue infections were traced to patients who had recently travelled from outside Delhi. Another 104 malaria and 626 dengue cases had incomplete addresses, while 76 malaria and 195 dengue patients could not be located despite address verification.

“These untraced cases remain a major problem because anti-mosquito drives rely on accurate location data to identify breeding hotspots,” said a senior public health official. “We have written to hospitals repeatedly asking them to ensure complete reporting of patient details.”

HT had on August 29 highlighted how “untraced cases” are keeping the official case count low and also hampering the anti-mosquito drives due to poor identification of clusters.

Despite the withdrawal of monsoon rains, MCD’s vector control teams continue to detect high mosquito breeding activity across the city. In the week ending September 29 alone, 11,307 mosquito-breeding sites were identified -- pushing the total for the year to 209,298, up from 196,000 during the same period last year.

“The problem is that scattered showers in late September continue to leave stagnant water in drains, flower pots, and construction sites,” the official said. “People should remain cautious until temperatures fall significantly — wear full sleeves, use repellents, and avoid water accumulation at home.”

MCD’s efforts, however, have been affected by an ongoing strike of domestic breeding checkers — ground workers responsible for identifying and eliminating breeding sites. This impact is likely to be visible in the next weekly cycle.

Experts believe this year’s dengue infections are milder, with fewer hospitalisations compared to previous years. “Milder dengue strains appear to be in circulation this year, and we are not seeing many severe or haemorrhagic cases,” the official said.

The official attributed the rise in malaria numbers not only to prolonged humidity but also to better reporting. “The surveillance network has improved, and private clinics are now more consistent in sharing data,” the official said.

Under a 2021 Delhi government notification, dengue, malaria, and chikungunya were declared notifiable diseases under the Epidemic Diseases Act, making it mandatory for all healthcare institutions to report cases. But the persistence of incomplete data, officials admit, “defeats the purpose of improved surveillance”.

“The mosquito that transmits dengue breeds in clean, stagnant water, while malaria vectors prefer smaller pools and ditches,” said a municipal health officer. “The only effective long-term control is source reduction -- ensuring no standing water is left in or around homes.”